FEMS Microbiology Reviews 27 (2003) 291^311

www.fems-microbiology.org

Zn(II) metabolism in prokaryotes


Dayle K. Blencowe, Andrew P. Morby

Cardi¡ School of Biosciences (2), Cardi¡ University, Museum Avenue, P.O. Box 911, Cardi¡ CF10 3US, UK Received 7 October 2002; received in revised form 29 January 2003; accepted 29 January 2003 First published online 26 April 2003

Abstract It is difficult to over-state the importance of Zn(II) in biology. It is a ubiquitous essential metal ion and plays a role in catalysis, protein structure and perhaps as a signal molecule, in organisms from all three kingdoms. Of necessity, organisms have evolved to optimise the intracellular availability of Zn(II) despite the extracellular milieu. To this end, prokaryotes contain a range of Zn(II) import, Zn(II) export and/or binding proteins, some of which utilise either ATP or the chemiosmotic potential to drive the movement of Zn(II) across the cytosolic membrane, together with proteins that facilitate the diffusion of this ion across either the outer or inner membranes of prokaryotes. This review seeks to give an overview of the systems currently classified as altering Zn(II) availability in prokaryotes. 3 2003 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved. Keywords : Metal ion; Zinc ; Ion transport; Metallo-chaperone

Contents 1.

Zinc in biology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1. Prokaryotic Zn(II) metabolism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Primary mechanisms of Zn(II) import . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. ZnuABC: a high-a⁄nity Zn(II) uptake system . . . . . . . . . . . . . . . . . . 3. Secondary mechanisms of Zn(II) import . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Nramp and Mramp: broad-spectrum cation transporters . . . . . . . . . . 4. Protein-speci¢c alterations in prokaryotic Zn(II) sensitivity . . . . . . . . . . . . 4.1. ZupT: a Zn(II) import system in E. coli . . . . . . . . . . . . . . . . . . . . . . 5. Broad-spectrum metal ion importers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1. Mg(II) uptake systems that also import a variety of other metal ions . 6. Metallo-chaperones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1. Cyanobacterial metallothioneins . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2. PZP1: a periplasmic Zn(II) metallo-chaperone in Haemophilus . . . . . . 6.3. Potential E. coli metallo-chaperones . . . . . . . . . . . . . . . . . . . . . . . . . 7. Primary mechanisms of Zn(II) export . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1. Cd(II) resistance in S. aureus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2. The zia operon of Synechocystis PCC 6803 . . . . . . . . . . . . . . . . . . . . 7.3. The zntA gene of E. coli . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8. Secondary mechanisms of Zn(II) export . . . . . . . . . . . . . . . . . . . . . . . . . . 9. Putative Zn(II) export systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1. A chromosomal Zn(II)/Co(II) resistance determinant in S. aureus . . . . 9.2. The zitB gene of E. coli and zntB from Salmonella enterica . . . . . . . . 10. Genomic approaches to Zn(II)-metabolism . . . . . . . . . . . . . . . . . . . . . . . . 11. Concluding remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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* Corresponding author. Tel. : +44 (2920) 874128; Fax: +44 (2920) 874116.

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E-mail address : morby@cardi¡.ac.uk (A.P. Morby).

0168-6445 / 03 / $22.00 3 2003 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved. doi:10.1016/S0168-6445(03)00041-X

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1. Zinc in biology Zinc, and indeed other transition metal ions, present an interesting chemical paradox to living cells. Whilst excess Zn(II) can have signi¢cant toxicity and can act as a potent disrupter of biological systems, it is also an essential (micro-)nutrient that plays important roles in numerous physiological processes [1^3], as it serves as a cofactor in members of all six major functional classes of enzymes [4] and is especially important in the maintenance of protein structure [5^10]. Zinc occurs naturally as the divalent cation Zn(II) (Zn2þ ) and has no redox activity under physiological conditions [11]. With the exception of copper, Zn(II) is the strongest intracellular Lewis acid and is predominantly coordinated to proteins via either the sulfur ‘thiol’ moieties of cysteine residues or the amino ‘imidazole’ ligands of histidine residues [12^16]. Although Zn(II) forms strong or labile co-ordinate bonds to these moieties, Zn(II) complexes tend to be thermodynamically stable [17]. 1.1. Prokaryotic Zn(II) metabolism Prokaryotic organisms are single cell entities that have immediate contact with their proximal environment and are separated from it by a set of cellular membranes. Since prokaryotic organisms are devoid of sub-cellular compartments, the major mechanisms that maintain cellular Zn(II) concentrations (Fig. 1) are limited to the highly regulated processes of Zn(II) import, metal ion sequestration by metallo-chaperones and Zn(II) export across the cytoplasmic membrane. The import and export of Zn(II) is accomplished by a mixture of unique bacterial transport proteins, and proteins that belong to ubiquitously distributed protein superfamilies that contain members identi¢ed in all three kingdoms. Uptake systems for Zn(II), as well as other essential metal ions, have to di¡erentiate between ions that are structurally very similar. Hence, most cells have two types of import systems : those that have high substrate speci¢city, which can be coupled to an energy source, and those that are non-speci¢c and are usually driven by the di¡usion gradient across the cytoplasmic membrane. Export systems for Zn(II) tend to have evolved to transfer metal ions of the same group across the cytoplasmic membrane, with ions being grouped on the basis of electronic structure and chemical similarity, e.g. Zn(II)/Cd(II)/Pb(II) or Ag(I)/Cu(I). Membrane transport mechanisms can be further categorised on the basis of thermodynamics into primary and secondary systems, depending upon the energy source used for active transport. Primary mechanisms utilise chemical energy to transfer metal ions across the cytoplasmic membrane, whereas secondary active transport mechanisms use the energy stored in electrochemical gradients for the same purpose [18].

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The regulation of most of these systems is controlled at the level of transcription and is mediated by metal-responsive regulators, which modulate expression of genes in response to respective substrate concentrations. Hence, the cellular level of loosely bound, labile Zn(II) is sustained at close to required levels in conditions of either metal ion limitation or excess.

2. Primary mechanisms of Zn(II) import 2.1. ZnuABC : a high-a⁄nity Zn(II) uptake system ABC transporters are comprised of one, but more often two, transmembrane proteins that form a pore in the membrane allowing the transport of a speci¢c substrate from one side of the membrane to the other [19^21]. On the cytosolic membrane face of this pore are one or two ATP-binding regions that act to provide the energy for substrate transport from ATP hydrolysis. The Znu proteins of Escherichia coli belong to a recently de¢ned subfamily of uniquely bacterial divalent metal ion ABC transport systems that are dependent upon an extra-cytoplasmic metal-binding protein [22]. The znu structural genes are transcribed in a divergent pattern on the chromosome from a spacer region that lacks the presence of an obvious promoter, with znuA being upstream and transcribed on the complementary strand to znuBC. Located next to znuA, and also transcribed from the complementary strand, is yebA, which encodes a hypothetical Zn(II)-dependent protease [23] of unknown function. YebA has signi¢cant similarity to the Zn(II)-containing staphylococcal enzyme, lysostaphin, which is an enzyme that degrades the cross-links in peptidoglycan and elastin [24]. ZnuA has primary sequence similarity to the periplasmic binding protein of the Mn(II) transport system of Synechocystis sp. [25] and has a cleavable periplasmic leader sequence [23]. This indicates that ZnuA is located outside the cytoplasmic membrane and has the potential to bind metal ions. ZnuB is a hydrophobic protein that has similarity to the membrane component of other ABC transport systems, whilst ZnuC has strong sequence similarities to the ATPase subunit of the ATP transporters [23]. Evidence obtained by Patzer and colleagues suggests ZnuABC constitutes a high-a⁄nity Zn(II) uptake system in E. coli that is functionally dependent on both ZnuA and ATP. This system is regulated by Zur, which is a member of the Fur family of bacterial metal-responsive regulators [23,26] and can sense sub-femtomolar concentrations of cytosolic Zn(II) [27]. In its native state Zur forms a dimer [28], which in the presence of excess Zn(II) binds to a regulatory sequence of dyad symmetry that is located within the central znu operator region and prevents the binding and activity of RNA polymerase. This Zur dimer

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293

ZN(II) IMPORT SECTION 3 SECONDARY IMPORT MECHANISMS

SECTION 4 PROTEIN SPECIFIC ALTERATIONS IN ZN(II) SENSITIVITY

SECTION 5 - BROAD SPECTRUM METAL ION IMPORTERS

Nramp and Mramp

ZIP family ZupT

Zn(II) uptake systems of diverse specificity, inc. Pit and Mg(II) uptake Systems I (MIT) & System II (Mgt)

SECTION 2 PRIMARY IMPORT MECHANISMS

ABC transporters

H+

H+

ADP

ATP

Possible Cytosolic e.g. the

(SECTION 6)

ADP

ATP

Porins

METALLO-CHAPERONES

Possible Periplasmic e.g. PZP1 from Haemophilus & ZraP

H+

H+

P-Type ATPases e.g. CadA, ZiaA & ZntA

RND transenvelope czc determinant

SECTION 7 PRIMARY EXPORT MECHANISMS

SECTION 8 SECONDARY EXPORT MECHANISMS

CDF family inc. ZntA from S. aureus, E. coli ZitB

SECTION 9 PUTATIVE ZN(II)EXPORT SYSTEMS

ZN(II) EXPORT Fig. 1. Protein families involved in prokaryotic Zn(II) tra⁄cking. In Gram-negative prokaryotes Zn(II) enters and leaves the periplasmic space via nonspeci¢c porin proteins. It is imported into the cytosol of prokaryotic cells via a variety of speci¢c and broad-spectrum transport systems. Once internalised into the cellular environment, Zn(II) is thought to be distributed by metallo-chaperones. Zn(II) is exported from the cell cytosol by metal ion-speci¢c transport systems that either translocate Zn(II) to the periplasm or mediate high-e⁄ciency trans-envelope e¥ux to the external environment. Annotations provide a guide to future section numbers.

is only active in the reduced form [28] and has two distinctive metal-binding sites [17]. The ¢rst binds Zn(II) very tightly and is functionally analogous to the Zn(II)-binding site in Fur, whereas Zn(II) is more readily exchanged in the second site, which is similar to the metal-sensing site in the Zn(II) metallo-regulatory protein SmtB from Synechococcus [17,29^31]. Zur proteins seem to be widespread among Gram-negative, Gram-positive and cyanobacteria ([28], and references therein). In addition, a number of homologous, ABCtype, Znu high-a⁄nity Zn(II) permease systems have also been identi¢ed in other bacteria. These include a system

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from Listeria monocytogenes [32], two from Haemophilus sp., [33^35] two from Streptococcus sp., [22,36,37] as well as systems in Treponema pallidum [38] and Neisseria gonorrhoeae [39]. A common Zn(II)-responsive metallo-regulatory protein (also designated Zur) is thought to regulate two coding regions that have been identi¢ed in Bacillus subtilis. These regions have been implicated in the high- and low-a⁄nity uptake of Zn(II) by this Gram-positive organism [40] and are thought to have a number of parallels with the ZRT Zn(II) transport systems that regulate Zn(II) uptake in the yeast Saccharomyces cerevisiae [41^47].

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3. Secondary mechanisms of Zn(II) import Secondary mechanisms of metal ion active transport, either uniporters or antiporters, catalyse the import or export of metal cations. The natural resistance-associated macrophage protein (Nramp) super-family [48] are a ubiquitous group of membrane proteins that are found in archaea, bacteria and eukaryotes and are associated with resistance to infection by intracellular pathogens [48^50]. Evidence suggests that members of the Nramp super-family use the electrochemical proton gradient as the major driving force for the broad-speci¢city import of divalent metal cations [49^57]. 3.1. Nramp and Mramp : broad-spectrum cation transporters Comparative genomic analyses have identi¢ed several Nramp homologues in micro-organisms such as Mycobacterium sp. (known as Mramp), Salmonella typhimurium and E. coli [58^61]. Functional characterisation of the E. coli Nramp homologue, designated MntH, con¢rms that, like its eukaryotic homologues, MntH is a protondependent divalent cation importer, which is able to facilitate the intracellular accumulation of several divalent metal ions, with substrate preference of Mn(II) s Cd(II) s Co(II) s Fe(II) s Zn(II) and to a lesser extent Ni(II) s Cu(II) [62]. MntH is regulated by the external availability of metal ions and by the dual action of the iron-dependent and manganese-dependent repressor proteins Fur and MntR [60,63]. It is possible that MntH represents the single Mn(II) active transport system that was identi¢ed by Bhattacharyya [64] and Silver et al. [65] in 1970.

4. Protein-speci¢c alterations in prokaryotic Zn(II) sensitivity In addition to the primary and secondary mechanisms of Zn(II) import in prokaryotes, proteins have been identi¢ed that confer Zn(II) sensitivity when expressed at high levels, which are indicative of further Zn(II) import systems. These proteins include a recently characterised bacterial member of the ZIP (ZRT, IRT-like protein) superfamily of metal ion transporters, previously reported only in eukaryotes [66^71]. 4.1. ZupT: a Zn(II) import system in E. coli Similar to the ZIP super-family members found in humans and yeast [46,72^77], ZupT from E. coli is involved in the uptake of Zn(II) across the cellular membrane and into the cell cytosol [68]. ZupT appears to have a lower a⁄nity for Zn(II) than the ZnuABC system and may also be a broad-range metal ion transport protein, potentially mediating the import of cations such as Cd(II) and possi-

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ble Cu(I) into E. coli cells [68]. This theory is consistent with the previously reported metal ion speci¢cities of the Arabidopsis thaliana ZIP proteins [70]. In addition to these cation-speci¢c metal ion transporters, Zn(II) may also be able to enter prokaryotic cells via a variety of other mechanisms, which have the ability to act as broad-spectrum metal ion importers.

5. Broad-spectrum metal ion importers The outer membranes of many bacteria, including E. coli, contain a group of proteins known as porins [78^80]. These proteins form cylindrical, £uid-¢lled channels in the outer membrane of cells that allow selective hydrophilic solutes of up to 600 Da, including divalent metal cations such as Zn(II), to di¡use across into the periplasmic space. Zn(II) may then be imported into the cytosol of cells such as E. coli as a neutral metal phosphate via the constitutively expressed inorganic phosphate uptake system (Pit) [81], which also transports a diverse array of other metal cations into the cell [82^85]. Zn(II) can also be imported into cells as an alternative substrate of many broad-spectrum Mg(II) uptake systems [86^88]. 5.1. Mg(II) uptake systems that also import a variety of other metal ions Mg(II) is the most abundant divalent cation in biological systems [89], and has the largest hydrated radius of all divalent cations of biological interest [90]. In E. coli there are two systems for Mg(II) uptake. System I is a higha⁄nity, fast and non-speci¢c metal transport system (MIT), designated CorA. CorA was identi¢ed as a Mg(II) uptake protein [87,91,92] and is ubiquitous throughout a variety of Gram-negative and Gram-positive bacteria [88,90,93,94] as well as in the yeast S. cerevisiae [95]. This system is constitutively expressed [90,96], and mediates the in£ux of Mg(II) as well as Ni(II), Co(II) and perhaps Zn(II) into the cytoplasm of E. coli cells [88]. System II is a speci¢c Mg(II) transport system [96,97] that is regulated in response to Mg(II) concentration [88,96]. System II is analogous to the Mgt system [97] and, like CorA, has homologues in many other organisms. Probably the best characterised system is from S. typhimurium [98^104], which includes MgtA, a P-type ATPase that may transport Zn(II) better than Mg(II) ([11] and references therein). There is over 88% similarity between the MgtA proteins from S. typhimurium and E. coli [105], which also catalyses ATP-dependent Mg(II) uptake [106]. Hence, there is the possibility that MgtA from E. coli also transports Zn(II) and may provide the energy-dependent Zn(II) uptake phenotype observed by Bucheder and Broda [107]. In addition to these Mg(II) transport proteins, two other proteins have also been shown to confer Zn(II) ion

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uptake into prokaryotic cells. MgtE from Bacillus ¢rmus OF4 is thought to be a Mg(II) and Co(II) uptake protein of diverse speci¢city that extends to incorporate Zn(II) import [90]. At present homologues of MgtE have been found in only one Gram-positive organism (B. ¢rmus) and in a limited variety of other Gram-negative bacteria, which include the opportunistic human pathogen Providencia stuartii, which is closely related to E. coli and S. typhimurium [94]. Similar to the broad-spectrum, non-speci¢c Mg(II) system I of E. coli, active divalent metal ion uptake has also been found in Ralstonia metallidurans. This system is strongly regulated by environmental Mg(II) concentration and is the principal importer of divalent metal cations, such as Zn(II), Cd(II), Co(II), Ni(II) and Mn(II), into the metal-sensitive, plasmid-free R. metallidurans strain (AE104) [108]. The active uptake of both Cd(II) and Zn(II) into E. coli cells has also been demonstrated independently [107,109]. Once internalised into either the cytoplasm or the periplasm of the cell, it is unlikely that potentially toxic transition metal cations such as Zn(II) are left to freely di¡use throughout the cell matrix. Hence, it has been suggested that metal ions are bound and subsequently distributed by a variety of metallo-chaperones.

6. Metallo-chaperones Chaperones, as the name implies, act to escort or usher interactive entities through the potentially hostile environments in which they ¢nd themselves, whilst facilitating appropriate partnerships. The primary function of chaperones is to protect, not only shielding the entity from the environment, but more often than not protecting the environment from the more active nature of its inhabitant, thus preventing unfavourable interactions between the two. A family of soluble metal-binding proteins, known as metallo-chaperones [110], are thought to facilitate the intracellular tra⁄cking of metal ions. In addition to the characterisation of the relatively new copper metallo-chaperones of eukaryotes [41,47,111^116] and potential bacterial chaperones [117^119], probably the best known biological molecule that sequesters metal ions and mediates metal-dependent gene expression is metallothionein (MT) [120^129]. However, even after extensive research, the biological function of MT remains unclear. Although MT is induced in many organisms as a consequence of exposure to toxic levels of metal ions, where it is thought MT acts as a protective ‘sponge’, this is likely to be a property of MT rather than an evolutionary function [128]. Evidence indicates that MT is not essential for metalloprotein synthesis [122,126,130]. However, it is possible that MTs might function as cytosolic metallo-chaperones of the more physiologically important metal ions such as

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Zn(II) and/or copper, serving as an internal transport mechanism that deliver these divalent cations to apo-metalloproteins [127,131^139]. In contrast to their eukaryotic relatives [140^147], bacterial MTs have not previously been widely reported. In Pseudomonas putida, there have been reports of three MTlike proteins [148^150], whereas Cd(II)-binding components have been isolated from E. coli [151]. Most recently bacterial metallothioneins (BmtA) (some corresponding to those initially reported in P. putida) have been isolated and characterised from a range of strains including Anabaena PCC7120, Pseudomonas aeruginosa, P. putida and E. coli, all of which bind Zn(II). It is of interest to note that some contain the GATA-type oneZn(II)-¢nger structure similar to that seen in SmtA, the best studied prokaryotic MT that has been identi¢ed in a range of cyanobacterial strains [152,153]. 6.1. Cyanobacterial metallothioneins SmtA is a small, non-essential, cysteine-rich protein that is found in cyanobacteria and has a comparatively high a⁄nity for Zn(II) in preference to Cd(II), Cu(II) and Hg(II) [152,154^159]. SmtA di¡ers from eukaryotic MT as it contains histidine residues [160]. The abundance of SmtA increases following the exposure of cyanobacterial cells to elevated concentrations of Zn(II) and Cd(II), but not Cu(II) [161], which is the result of an increased level of smtA transcripts [157]. The chromosomal smtA locus along with smtB, the gene encoding its trans-acting metal-dependent repressor [29], is divergently transcribed from a central operator^promoter region [158]. SmtB is member of the ArsR family of metallo-regulatory proteins [162,163] and represses the expression of smtA by binding to an imperfect inverted repeat that is situated between the sites of transcriptional and translational initiation of smtA [30,157]. It may also bind to the two other regions of the operator^promoter region in a multimeric form at higher concentrations [29,30]. This regulation is then sensitive to £uctuations in metal ion concentrations, with the potential tetrahedral binding of Zn(II) by an SmtB homodimer complex causing dissociation of SmtB from its principal promoter complex or either of its two other potential regulator binding sites [31,164]. Although the suggestion that MT can form a putative cytosolic Zn(II)-translocating metallo-chaperone is only tentative, periplasmic proteins have been identi¢ed in a number of bacterial species that could be classi¢ed as Zn(II)-translocating metallo-chaperones. Principally these include the periplasmic ZnuA protein orthologues of the bacterial ABC metal permeases as well as PZP1, a Zn(II)binding periplasmic metallo-chaperone from Haemophilus in£uenzae.

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6.2. PZP1 : a periplasmic Zn(II) metallo-chaperone in Haemophilus With the completion of the H. in£uenzae genome sequence [165] came the identi¢cation and partial characterisation of a putative adhesin B protein, periplasmic zincbinding protein- (PZP1) [33,34]. This 37-kDa periplasmic protein shows signi¢cant similarity (49.2% identity/59.4% similarity) to ZnuA from E. coli and is thought to be involved in the uptake of Zn(II) into H. in£uenzae [23,33]. Since a null mutation made in the pzp1 coding sequence confers a Zn(II)-dependent growth phenotype on cells grown aerobically, it is likely that PZP1 is part of the major Zn(II) uptake system in this pathogenic prokaryote. Sequence analysis indicates that PZP1 has similarity to another putative adhesin B protein that contains an ATP-binding cassette [165] and it has been speculated that PZP1 and this uncharacterised protein may interact, possibly with other protein(s), to form a Zn(II) import system [33], similar to the Znu system from E. coli [23]. 6.3. Potential E. coli metallo-chaperones Other proteins in E. coli that have the potential to form Zn(II)-binding metallo-chaperones include an unidenti¢ed 20-kDa periplasmic spy protein that is only produced when cells are incubated with millimolar concentrations of Zn(II) [166,167], YdaE and ZraP (formerly YjaI). YdaE has signi¢cant primary structural similarity with SmtA from Synechococcus and has recently been shown to interact with Zn(II) [153]. ZraP is a 20.4-kDa membrane-associated protein that undergoes a speci¢c Zn(II)-induced cleavage to release a 12-kDa carboxy-terminal Zn(II)-binding region into the periplasm, which is involved in acquisition of tolerance to high Zn(II) concentrations. The expression of zraP is regulated by ZraS and ZraR (formerly HydH and HydG, respectively), which may form part of a Zn(II)-responsive phosphorylation cascade [166,168]. It is interesting to note the recent report detailing the release of Zn(II) ions bound to SmtA expressed in E. coli due to nitric oxide exposure [169]. Further studies of such phenomena certainly may well prove illuminating in terms of the global cellular function of Zn(II). The identi¢cation of Zn(II) chaperones represents a beginning of the dissection of pathways that carry Zn(II) within the cell and target it to speci¢c cellular sites. Such studies hold a great deal of promise for understanding the cellular consequences of Zn(II) metabolism.

of proteins that can be separated into protein families and can be grouped on the basis of thermodynamics. However, unlike the systems that import Zn(II) into the cell cytosol, the proteins that export Zn(II) across the cytoplasmic membrane into the periplasm often have more precise substrate speci¢cities. Like the primary mechanisms of Zn(II) import, the proteins involved with the export of Zn(II) can also utilise the energy derived from ATP hydrolysis to translocate metal cations across the cytoplasmic membrane. Perhaps the best studied super-family of these proteins are the P-type ATPases. One sub-group of this super-family involved in transition metal ion export are the ‘soft metal ion-translocating’ P-type ATPases [13,170^174], which can be further sub-divided into two classes [13]: the Cu(I)/Ag(I)translocating ATPases and the Zn(II)/Cd(II)/Pb(II)-translocating proteins (Fig. 2). Representative members of these sub-family groups of P-type ATPases, which appear to be present in all three kingdoms, include the Cd(II)/Zn(II)/Pb(II) export protein CadA, from Staphylococcus aureus [175,176] and the Cu(I)/Ag(I)-transporting CopA and CopB from Enterococcus hirae [177^180], as well as proteins associated with both Wilson’s and Menkes’ diseases [181^186]. More recently, members that transport Ag(I), Co(II) or Pb(II) have also been identi¢ed [187^190]. These integral membrane ATPases form an important class of ion transport proteins that serve to maintain suitable cellular ionic conditions [173] and are characterised by the transient formation of a covalent phosphorylated intermediate during the catalytic cycle [170,171,191,192], as well as consensus domains for both ATP binding and hydrolysis [173]. The energy released by the removal of the Q-phosphate from ATP is coupled to the translocation of ions across biological membranes. In addition, these soft metal ion-translocating proteins, which have also been designated the ‘CPx-type ATPases’ [173] or ‘P1 heavy metal-transporting P-type ATPases’ [174], exhibit several novel features. These include unique number and topology of the membrane-spanning segments located in the carboxyterminal region of the protein [193,194] as well as distinctive, highly polar, amino-terminal regions that contain one to six repeats of a conserved metal-binding domain. These domains are 70^100 amino acids in length and most commonly contain a motif sequence with similarity to the ‘heavy metal-associated (HMA) motif’, GMTCxxC (where x is equivalent to any amino acid) [181,195] (Fig. 3). One of the ¢rst Zn(II)/Cd(II)- and Pb(II)-translocating members of this sub-family of proteins was identi¢ed in Cd(II)resistant strains of S. aureus. 7.1. Cd(II) resistance in S. aureus

7. Primary mechanisms of Zn(II) export Similar to the systems for Zn(II) import into prokaryotic cells, the systems for Zn(II) export are also made up

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Initial studies showed that genes encoding Cd(II) resistance were carried on several ‘penicillinase’ plasmids [196], the best characterised example of which is pI258 of S. aureus.

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297

P1 ‘soft-metal-ion’ translocating ATPases

P-type ATPases super-family P2 ‘Ca2+, Na2+ / K+ and H+ / K+ translocating ATPases P3 ‘H+ and Mg(II)’ translocating ATPases P4 ‘phospholipid’ translocating ATPases P5 ATPases (no assigned function) Fig. 2. Organisation of the P-type ATPase super-family highlighting the phylogenetic relationship of the primary structures of the soft metal ion-translocating sub-group. The ¢ve sub-groups of the P-type ATPase super-family are spatially arranged. The dendrogram representing the sub-group of soft metal ion-translocating ATPases (highlighted in box) has been reproduced from Rensing [13] with GenBank accession numbers for each representative member given therein. Brie£y: Zn(II)/Pb(II)/Cd(II) pumps include ZntA E. coli (P37617), CadA from B. ¢rmus (AAA22858) and that encoded by the S. aureus plasmid pI258 (AAB59154). Cu(I)/Ag(I) pumps include MNK, human Menkes’s disease-related protein (Q04656), WND, human Wilson’s disease-related protein (U03464) and CopA from E. coli (AAB02268). The sub-group of soft metal ion-translocating P-type ATPases is growing rapidly, so only representative members are shown. The calculated matching percentages are indicated at each branch point.

This bacterium is a common human pathogen that is associated with a number of diseases. Its plasmid-encoded Cd(II) resistance operon consists of two overlapping open reading frames [175]. The ¢rst, cadC, encodes a 122-amino acid, soluble protein and the second, cadA, encodes a 727-amino acid, integral membrane protein. CadA from S. aureus is a soft metal ion-translocating P-type ATPase [13,174,197], and confers resistance to Cd(II), Zn(II) and Pb(II) [175,198^201]. The topology of CadA, encoded on plasmid pI258, has been determined [202] and conforms to that predicted for the soft metal ion-transporting P-type ATPase sub-family [173,174,193,203,204] (Fig. 4). CadA catalyses the ATP-dependent e¥ux of Cd(II) from the cell cytosol in an electro-neutral exchange that transfers one Cd(II) ion out of the cell whilst accumulating two protons [175,176,205]. Unsurprisingly, the cadmium resistance operon is primarily induced by Cd(II) [200]. Whilst Zn(II) appears to be a rather poor inducer of the

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system [200], the range of cation concentrations tested during induction pro¢ling was limited to a maximum of 100 WM, far below the toxic level for Zn(II). CadC is an extrachromosomally encoded metallo-regulatory repressor protein of the ArsR super-family of metallo-regulatory proteins [162,206^208] and negatively regulates expression of the cad operon in response to metal ions. The binding of thiophilic divalent cations, including Cd(II), Zn(II) and Pb(II), to this trans-acting repressor protein allosterically regulates the DNA-binding activity of CadC to the cad operator region, CadC binding to the proposed region as a high-a⁄nity DNA^CadC dimer in the absence of metal ions and dissociating in the presence of the inducers [199,200,209^214]. The presence of cadC in the operon is essential for its ability to confer maximal resistance to metal ions [199,200]. When produced, CadC chelates metal ions using at least three cysteine residues, which are conserved in all CadC homo-

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Metal binding pocket (HMA loop)

β1

Metal binding pocket (Phe loop)

αa

β2

β3

β4

αb

10 20 30 40 50 60 70 ....|....|....|....|....|.. ..|... .|....|....|....|.... |....|.. ..|.. ..|.. ZntA E. CadA B. CadA S. MerP S. MerA S. MerA P. MerA T. MNK mbd MNK mbd MNK mbd MNK mbd MNK mbd MNK mbd WD mbd WD mbd WD mbd WD mbd WD mbd WD mbd CopA E. CopA E. CopA E. Atx1 S. Hah1 H. CopZ E.

coli firmus aureus flexneri flexneri aeruginosa ferrooxidans 1 2 3 4 5 6 1 2 3 4 5 6 coli mbd 1 coli mbd 2 hirae cerevisiae sapiens hirae

~SGTRYSWKVSGMDCAACARKVENAVRQ-LAGVNQ-VQVLFATEKLVVDADNDIRAQVES---ALQK-AGYS---LRD ~EQEMKAYRVQGFTCANCAGKFEKNVKQ-LSGV-EDAKVNFGASKIAVYGNATIEEL-EKA-GAFEN-LKVTPEKSAR ~EEEMNVYRVQGFTCANCAGKFEKNVKK-IPGV-QDAKVNFGASKIDVYGNASVEEL-EKA-GAFEN-LKVSPEKLAN ~ATQTVTLAVPGMTCAACPITVKKALSK-VEGVSK-VDVGFEKREAVVTFDDTKASV-QKLTKATA-DAGYP-SSVKQ MSTLKITGMTCDSCAVHVKDALEK-VPGV-QSADVSYAKGSAKLAIEVG-TSP-DALTAAVAG-LGYR-ATLAD MTHLKITGMTCDSCAAHVKEALEK-VPGV-QSALVSYPKGTAQLAIVPG-TSP-DALTAAVAG-LGYK-ATLAD ~ENAPTELAITGMTCDGCAAHVRKALEG-VPGV-REAQVSYPDATARVVLEGEV--PMQRLIKAVVA-SGYG---VHP ~GVNSVTISVEGMTCNSCVWTIEQQIGK-VNGVHH-IKVSLEEKNATIIYDPKLQTP-KTLQEAID-DMGFD-AVIHN ~GEVVLKMKVEGMTCHSCTSTIEGKIGK-LQGV-QRIKVSLDNQEATIVYQPHLISV-EEMKKQIE-AMGFP-AFVKK ~NDSTATFIIDGMHCKSCVSNIESTLSA-LQYV-SSIVVSLENRSAIVKYNASSVTP-ESLRKAIE-AVSPGLYRVS~ ~LTQETVINIDGMTCNSCVQSIEGVISK-KPGV-KSIRVSLANSNGTVEYDPLLTSP-ETLRGAIE-DMGFD-ATLSD ~NSSKCYIQVTGMTCASCVANIERNLRR-EEGI-YSILVALMAGKAEVRYNPAVIQP-PMIAEFIR-ELGFG-ATVIE ~GDGVLELVVRGMTCASCVHKIESSLTK-HRGILYCS-VALATNKAHIKYDPEIIGPRDIIHT-IE-SLGFE-ASLVK ~QVATSTVRILGMTCQSCVKSIEDRISN-LKGII-SMKVSLEQDSATVKYVPSVVCL-QQVCHQIG-DMGFE-ASIAE ~QEAVVKLRVEGMTCQSCVSSIEGKVRK-LQGVVR-VKVSLSNQEAVITYQPYLIQP-EDLRDHVN-DMGFE-AAIKS ~HVVTLQLRIDGMHCKSCVLNIEENIGQ-LLGV-QSIQVSLENKTAQVKYDPSCTSP-VALQRAIE-ALPPGNFKVS ~TCSTTLIAIAGMTCASCVHSIEGMISQ-LEGVQQ-ISVSLAEGTATVLYNPSVISP-EELRAAIE-DMGFE-ASVVS ~APQKCFLQIKGMTCASCVSNIERNLQK-EAGVL-SVLVALMAGKAEIKYDPEVIQPLE-IAQFIQ-DLGFE-AAVME ~SDGNIELTITGMTCASCVHNIESKLTR-TNGIT-YASVALATSKALVKFDPEIIGPRD-IIKIIE-EIGFH-ASLAQ MSQTIDLTLDGLSCGHCVKRVKESLEQ-RPDVEQ-ADVSI-T-EAHVTGTASAEQLIETIKQAGY-DASVSHPKA-K ~DDDSQQLLLSGMSCASCVTRVQNALQS-VPGVTQ-ARVNLAERTALVMGSAS---PQDLV-QAVE-KAGYG-AEAIE ~NTKMETFVITGMTCANCSARIEKELNE-QPGVM-SATVNLATEKASVKYTDT-TT--ERLIKSVEN-IGYG-AILYD ~EIKHYQFNVVMTCSGCSGAVNKVLTKLEPDVSK-IDISLEKQLVDV-YTT-LPYD-FILEK-IKK-TGKEVRSGKQ MPKHEFSVDMTCGGCAEAVSRVLNK-LGGV-K-YDIDLPNKKVCIESEHSMDTL-LATLK--K-T-GKTVSYLGL MKQEFSVKGMSCNHCVARIEEAVGR-ISGVKK-VKVQLKKEKAVVKFDEANVQATE-ICQAI-NELGYQ-AEVI

Fig. 3. Multiple alignment of the amino acid sequences from domains containing potential HMA motifs. These include the HMA motif domains from the Zn(II)/Cd(II)- and Cd(II)/Zn(II)-transporting ATPases ZntA and CadA [175,215,238], as well as the domains from the Hg(II) chaperone MerP [323^325] and the MerA homologues with unknown function [323,324]. Also included are the six putative metal-binding domains of the Cu(I) ATPases from Menkes’ protein (MNK mbd 1^6) and Wilson’s disease (WD mbd 1^6) proteins [181,183,185,326] ; the two from the E. coli CopA Cu(I) transporter [179] and one from CopA in E. hirae [177,242] ; as well as the metal-binding and putative metal-binding domains of a series of other proteins including the Cu(I) chaperones Atx1, Hah1 and CopZ [112,178,327]. The block shading indicates the positions of conserved or highly similar residues across all the protein regions shown. The positions of secondary structure elements are represented at the top of the ¢gure along with the positions of the metal-binding pockets from MerP, CopZ and MNK metal-binding domain 4 [119,195,328,329]. If a sequence is preceded by V, this indicates the presence of amino-terminal extensions.

logues, and potentially a single carboxylic acid group, which is conserved as either an aspartate or a glutamate in all identi¢ed members of the ArsR family [210]. Bacterial resistance to Cd(II) is usually based on the e¥ux of this divalent metal ion and Cd(II) resistance determinants are widespread [175,215^218]. Although the founder members of the growing group of Cd(II) resistance determinants were ¢rst identi¢ed in S. aureus [198,219,220], plasmid-borne Cd(II)-resistant determinants have been more recently identi¢ed in Helicobacter pylori [193,203,204,221^223], Staphylococcus lugdunensis [224, 225], S. aureus [226,227], P. putida [228], Ralstonia strains

--

(section 1.11.1) and in clinical isolates of L. monocytogenes [216,229,230]. In addition, chromosomally encoded determinants have also been identi¢ed in Stenotrophomonas maltophilia [231] and various Pseudomonas species [232,233]. Although these proteins were initially characterised because of the ability to confer Cd(II) tolerance, in many cases, Zn(II) resistance determinants were genetically indistinguishable from those conferring resistance to Cd(II). Other members of the soft metal ion-translocating P-type ATPases family, such as ZiaA from Synechocystis PCC 6803 and ZntA from E. coli, were primarily identi¢ed be-

-

-

--CPC

+++ GFTCANC

+

++

+ TGES

DKTGT

+++ GDGVNDAP

COOH

EYRSQHP

Fig. 4. Membrane topology of CadA, a Cd(II) and Zn(II) e¥ux protein (adapted from [202]).

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cause of the ability to modulate Zn(II) concentrations in cells. 7.2. The zia operon of Synechocystis PCC 6803 The zia system was identi¢ed in the fully sequenced genome of the cyanobacterium Synechocystis PCC 6803 [234] and comprises two open reading frames, ziaA and

299

ziaR, which encode a Zn(II) transport protein and its cognate regulator and are divergently transcribed from a central promoter region [235]. ZiaA is a soft metal ion-translocating P-type ATPase that has sequence similarity to CadA. Whilst the expression of ziaA, under the control of its upstream regulatory sequences, confers both an increased Zn(II) tolerance and a reduction in Zn(II) accumulation by cells, its disruption leads to Zn(II) hypersen-

Fig. 5. Alignment of the primary structure of ZntA with its CadA homologue from B. ¢rmus and that encoded by the S. aureus plasmid pI258. Identical residues are boxed in grey with similar residues coloured in blue. Some of the characteristic features of soft metal-transporting P-type ATPases are coloured in red. Other potential metal-binding residues are highlighted in green. The protein sequence for ZntA is taken from [238], that for B. ¢rmus from [175] and that for S. aureus plasmid pI258 from [215].

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sitivity and a reduced periplasmic compartmentalisation for this ion [235]. Hence, ZiaA mediates the e¥ux of Zn(II) from the cell cytosol to the periplasmic space of cyanobacterial cells. ZiaR belongs to the ArsR super-family of metal-responsive repressor regulators [162] and binds to the zia operator^promoter region in the absence of Zn(II), forming a Zn(II)-responsive repressor of ziaA transcription [235]. The perception of Zn(II) by ZiaR is conferred by the histidine residue at position 116 and either or both cysteine residues located at positions 71 and 73 of the primary structure [235]. It has been suggested that ziaR and the upstream open reading frame, sll0793, which is predicted to encode a membrane-bound protein, are co-transcribed as there is only an 11-bp spacer region between them. This implies that sll0793 may also be involved in mediation of Zn(II) by the zia system. However, as yet, there is no evidence to support this. A more extensive review of this subject by Cavet et al. appears in this issue [160]. In addition to these systems, E. coli also contains two open reading frames that encode proteins belonging to the soft metal ion-translocating P-type ATPase family. The ¢rst has now been designated copA and encodes a Cu(I) and possibly Ag(I) export protein [179,236], the second is zntA [237^239]. 7.3. The zntA gene of E. coli The zntA gene from E. coli encodes a member of the P-type ATPase super-family [240] and displays sequence similarity to a range of metal-translocating P-type ATPases from a diverse array of organisms [13,177,179,183,185, 235,241^248]. Most notably these include strong primary structural similarity to CadA (Fig. 5). zntAEcol encodes a 732-amino acid residue, approx. 77-kDa integral cytoplasmic membrane protein, which has all the hallmarks of a soft metal ion-translocating P-type ATPase (Fig. 6). These features include a cysteine-rich hydrophilic amino-terminal region that contains both a single metal-binding motif (GMDCAAC) and a unique triplet thiol cluster located

within a CCCDGAC motif. ZntAEcol also has a number of potential membrane-spanning segments within its carboxyterminal region that are interspersed with two additional cytosolic regions. Contained within the larger, 280-amino acid aspartyl kinase domain, is the hallmark phosphorylation motif, Asp-Lys-Thr-Gly (DKTG). Located within the smaller 145-amino acid phosphatase domain, which is situated further to the amino-terminus, is a Thr-GlyGlu-Ser (TGES) motif that is thought to be involved in the hydrolysis of the phospho-intermediate (Fig. 6). ZntAEcol is a Zn(II)-dependent Zn(II) and Cd(II) export protein that catalyses the energy-dependent e¥ux of Zn(II) and Cd(II) from the cell cytosol and has the ability to confer Zn(II)/Cd(II) and Pb(II) tolerance to E. coli cells [201,237,238,249], with the expression of zntAEcol resulting in a reduction in the amount of 65 Zn(II) associated with E. coli cells [249] and interruption at the 5P end of zntAEcol causing increased cellular Zn(II) association in Zn(II)-supplemented medium [239]. These studies also suggest that ZntAEcol is the primary mechanism of modulating Zn(II) concentration in the E. coli system as cells were unable to adapt to the altered levels of Zn(II) [249] and everted vesicles prepared from E. coli vzntA exhibited no accumulation of 65 Zn(II) [238]. In addition, the amino-terminal region of ZntAEcol confers both Zn(II) and Cd(II) tolerance to E. coli cells and forms a metal-binding domain that sequesters 65 Zn(II) during in vitro binding assays [249]. The function(s) of this sequestration event remains to be demonstrated. Moreover, the true functional roles of the putative amino-terminal metal-binding domains of soft metal iontranslocating ATPases are unknown. It is estimated that the Michaelis constant (KM ) of Zn(II) transport by ZntAEcol is in the range of approximately 10 WM, which is thought to be similar to the labile intracellular Zn(II) concentration and therefore enables E. coli to respond to minor changes in cytosolic content [238]. These results are consistent with data obtained by Okkeri and co-workers, who have shown that ATPase activities of ZntAEcol reached a maximal turnover rate when stimulated by 20 WM Zn(II) [250]. In addition, this

CPC

GMDCAAC CCCDGAC Amino-terminal region

TGES

Phosphatase domain

COOH

DKTG GDGINDAP EQGATHP

Aspartyl kinase domain

Fig. 6. The predicted topology of ZntAEcol . The primary structure of ZntA [238] can be modelled on the topology of soft metal-transporting P-type ATPases. The three major cytosolic regions are marked. The characteristic motifs of soft metal-transporting P-type ATPases, including the phosphate hydrolysis motif (TGES) of the phosphatase domain, the phosphorylation motif (DKTG) and the ATP-binding motif (GDGINDAP) of the aspartyl kinase domain, are also marked. In addition, the amino-terminal metal-binding motif (GMDCAAC), transmembrane CPC and conserved HP doublet (located within the Ex4 HP motif) and other potential metal-binding residues, including the triplet thiol cluster, are also shown.

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group has shown that there are two major Zn(II)-induced, vanadate-sensitive membrane proteins that are phosphorylated by Q-33 P-labelled ATP [250]. These correspond to the predicted monomer and dimer sizes of ZntAEcol , which is consistent with the archetypal dimerisation of P-type ATPases [171,194]. The metal ion-stimulated ATPase activity of puri¢ed, reduced ZntAEcol has shown that the ‘hard’ metal cations Ca2þ , Naþ and Ba2þ or the ‘soft’ metals Co(II), Ni(II), 3 Cr(III), Cu(I and II), SbO3 2 and AsO2 did not stimulate any ATPase activity, whereas both Pb(II) and Zn(II) stimulated activity between pH 5.5 and pH 8 (the total range investigated) [251]. These results are similar to those obtained by Okkeri and co-workers who also demonstrated that ATPase activity was stimulated by Pb(II) [250]. However, Sharma and co-workers [251] place the order of activity as Pb(II) s Zn(II) s Cd(II) at pH 6.0, Okkeri has an order of Zn(II) s Pb(II) s Cd(II). Thiolate complexes of Cd(II) and Hg(II) were also able to stimulate the ATPase activity of ZntAEcol at neutral pH [251]. It is interesting to note that during these investigations an oxidised form of ZntAEcol was not active, suggesting that the ability of the protein to translocate metal ions might depend on its cysteine residues, and that these residues may be easily oxidised. Metal ion speci¢city studies have shown that transition metal ions can have e¡ects on either ZntAEcol -P hydrolysis or the phosphorylation state of ZntAEcol [250]. This is borne out by the di¡ering e¡ects that substrate ions have on the transition metal ion transport cycle of this P-type ATPase. Whilst Zn(II) stimulates both ZntAEcol -P hydrolysis and ZntAEcol phosphorylation, Cd(II) is more e¡ective at promoting ZntAEcol phosphorylation and is less e¡ective at stimulating ZntAEcol -P hydrolysis and metal ion transfer [250]. Whilst this demonstrates that these two metal ions a¡ect di¡erent parts of the reaction cycle, it has been suggested that ZntAEcol has at least two functionally di¡erent metal-binding sites with slightly di¡erent speci¢cities [250]: one that is involved in the hydrolysis of the ZntAEcol -P intermediate and could be synonymous with the binding site for the ion to be translocated, and another which is involved in the catalysis of phosphoryl transfer from ATP to ZntAEcol . At present the locations of metal-binding sites in ZntAEcol and indeed other soft metal ion-translocating P-type ATPases are being mapped. However, the function of these sites in the metal ion translocation pathway remains unclear. Whilst the conserved metal-binding sites within the amino-terminal regions of ZntAEcol and its homologues clearly bind metal ions [195,249,252,253], these regions appear not to be essential for enzyme phosphorylation [250] or metal ion translocation [230,254,255]. Additionally, the unique CPx motif (where x can be cysteine, histidine or serine) may also have the ability to transiently sequester metal ions during the metal ion transport cycle. This signature motif is located within the sixth putative

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301

membrane-spanning segment of ZntAEcol , as well as many if not all soft metal ion P-type ATPases, and is thought to be situated in the transmembrane ion channel or the ion translocation domain [173]. Of particular functional interest is the Ex4 HP cluster (a motif located 34^43 residues distal from the aspartate residue in the ^DKTG^ phosphorylation motif that contains a conserved histidine-proline doublet sequence characteristic of soft metal ion-translocating P-type ATPases) [250]. This motif is involved in the metal ion transport cycle of ZntAEcol and possibly of other soft metal ion-translocating P-type ATPases as mutations (Glu470 Ala and His475 Gln) made within this cluster reduce metal ion stimulation of ATPase activity of ZntA [250], implying that these residues are involved in the binding and/or sensing of metal ions. Furthermore, these mutations correspond to those found within the Cu(I)-transporting P-type ATPases associated with Wilson’s and Menkes’ disease states, where they lead to reduced Cu(I) transport, either reducing the uptake of Cu(I) from the gut and other tissues (in Menkes’ disease) or conferring a lack of Cu(I) export in the liver resulting in excess Cu(I) in the brain and liver (in Wilson’s disease) [182^186,256^258]. 7.3.1. Transcriptional control of zntAEcol expression The expression of zntAEcol is under the control of ZntREcol , a trans-acting activator that is essential for the Zn(II)-induced transcription of zntAEcol [259^261]. ZntREcol exhibits 34% identity with the MerR metallo-regulatory protein, which is required for the Hg(II)-induced expression of the plasmid- and transposon-encoded mercury detoxi¢cation systems [262^270]. Similar to MerR, ZntREcol acts as a dimeric metallo-regulatory protein and tightly binds to its cognate promoter, PzntA (located upstream of the zntA start codon), regardless of the presence of a bound metal ion [259,271]. The PzntA promoter is reminiscent of the archetypical mer promoters from Tn501 and Tn21 transposon-encoded mercuric ion resistance mechanisms [272,273]. The separation of the 310 and 335 regions of the c70 promoter sequence of PzntA is 20 bp. This promoter structure not only extends the spacer region between the elements from the consensus 17 W 1 bp [274], but also de¢nes a rotational separation around the DNA helix, which together makes PzntA a poor substrate for the binding of the c70 subunit of RNA polymerase. Located within the spacer region of PzntA is a perfect 11^11-bp inverted repeat, which is slightly o¡set towards the 335 element [259] and is the binding site for the ZntREcol dimer [259,271]. ZntREcol regulates transcription from PzntA by a metalinduced DNA distortion mechanism that is thought to be a widespread attribute of the MerR family members [264,270,271,275^281]. Similar to the Hg(II) MerR activation of mer promoters [10], ZntREcol -dependent expression from PzntA exhibits a sigmoidal response to changes in the Zn(II) concentration, with induction occurring from 100

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WM to a maximum 75-fold increase at 1.1 mM Zn(II) [259]. Furthermore, ZntREcol has a femtomolar sensitivity to Zn(II) ions [282] and can bind up to two Zn(II) ions per monomer [271], which makes it one of the most sensitive regulatory proteins characterised to date.

8. Secondary mechanisms of Zn(II) export Probably the best characterised system of Zn(II) transfer that employs a secondary mechanism is encoded by the czc determinant from R. metallidurans (formerly Alcaligenes eutrophus or Ralstonia eutropha) [283^289] strain CH34, which contains at least eight determinants that encode resistance to metal ions [189,286,287,289^291] that are found on either the bacterial chromosome or one of two large, endogenous mega-plasmids, pMOL28 (180 kb) [292] and pMOL30 (238 kb) [284,286]. Of these R. metallidurans CH34 has three ‘classical’ plasmid-encoded metal resistance systems of diverse speci¢city. These include: chr, carried on pMOL28 and encoding resistance to chromate (CrO23 4 ) [293^295]; cnr, which is also found on pMOL28 where it confers resistance to Co(II) and Ni(II) [293,296^ 301] ; and czc, which mediates resistance to Co(II), Zn(II) and Cd(II) [290,294,302,303] and is encoded on the larger pMOL30 plasmid [284]. Both the cnr and czc systems are very closely related, with equivalent tri-component, chemiosmotic e¥ux systems that are functionally very similar [303^306]. These two systems have become the ¢rst members of a new bacterial family of resistance, nodulation and cell division (RND)-driven transporters [307,308] that channel cations across both inner and outer membranes and the periplasmic space, with the czc determinant becoming the archetype to which all new members of this family of ‘transenvelope transporters’ [309,310] are compared. Many ‘czc-type’ systems have now been isolated ; these include many from the Ralstonia spp. of L-Proteobacteria [286,287,289,311], possible determinants from S. aureus [312,313] and one involved in mammalian host cell cytopathicity by Legionella pneumophila [314]. In addition, similar systems have been identi¢ed in P. aeruginosa strains isolated from metal-polluted environmental sources and within the clinical isolate P. aeruginosa type (PAO1) [233]. These RND-driven transport systems are reviewed in detail by Nies [315], elsewhere in this issue.

9. Putative Zn(II) export systems 9.1. A chromosomal Zn(II)/Co(II) resistance determinant in S. aureus Staphylococcal strains that lack the plasmid-encoded

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heavy metal resistance determinants identi¢ed by Novick [198] still show resistance to some heavy metal ions. In the recent past Xiong and Jayaswal [313] have identi¢ed a chromosomal determinant that confers resistance to both Zn(II) and Co(II). Isolated from a genomic library, the region of DNA containing this determinant comprised two consecutive open reading frames, here designated zntASaur and zntRSaur , which encode proteins that show signi¢cant similarity to the cation di¡usion facilitator (CDF) super-family of proteins [46,66,304,316], and the ArsR family of regulators, respectively. The genomic organisation suggests that zntASaur and zntRSaur are co-transcribed in an operon, which encodes a Zn(II)/Co(II) export pump and its cognate regulatory protein [313,317]. The ZntASaur protein is predicted to have six transmembrane segments ending with a hydrophilic C-terminal region. Interestingly, ZntASaur contains two histidine-rich regions, one located near the amino-terminus and the other at the carboxy-terminus, which have the potential to coordinate metal ion binding. A genomic knockout of zntASaur conferred a Zn(II)- and Co(II)-sensitive phenotype to the host strain, which was complemented by the re-introduction of a trans copy of the intact operon into the strain [313]. The sensitive strain also accumulated more cytosolic Zn(II). When present in multiple copies, the zntSaur operon conferred a Zn(II)/ Co(II)-tolerant phenotype with multiple copies of zntSaur leading to a decreased intracellular Zn(II) content [313]. Together these data suggest that the zntASaur gene product is involved in the export of Zn(II) ions from S. aureus cells. Since sequence analysis revealed the lack of any characteristic ATP-binding sites in the ZntASaur primary structure, this indicates that transport of metal ions is powered by an alternative energy source or mechanism [313]. 9.2. The zitB gene of E. coli and zntB from Salmonella enterica Other proteins that have been associated with variations in Zn(II) tolerance of E. coli cells include ZitB (formerly YbgR), another member of the CDF family of proteins that is thought to mediate a speci¢c Zn(II)-induced Zn(II) e¥ux [318]. Analysis of ZitB has shown that a number of residues are essential for function (His53 , His159 , Asp163 and Asp186 ) and that neither the N- or C-terminal histidine-rich regions were essential for function [319]. More recently a novel Zn(II) export system has been identi¢ed in Salmonella enterica serovar Typhimurium [320]. ZntB is homologous to the CorA family of cation transporters that, surprisingly, is unable to function as a Mg(II) uptake system. Instead this protein appears to function as a novel Zn(II) e¥ux pathway in enteric bacteria that confers tolerance to both Zn(II) and Cd(II) [320].

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10. Genomic approaches to Zn(II)-metabolism Transcriptional pro¢les have been established for E. coli cells adapted to grow in media containing substantially elevated levels of a range of transition metal ions, including Zn(II) [321]. The data suggest that a number of gene products, previously unconnected with Zn(II), appear to play a role in the generation of tolerance. Expression of the transposition-associated protein InsA7 can confer a slight growth advantage on E. coli when challenged by Zn(II) or Cd(II). In silico analysis of the primary sequence of InsA7 highlighted the presence of two CxxC motifs that are associated with protein^cation interactions. These studies also identi¢ed a range of other genes whose products have either been shown to bind metal ions or are predicted to do so. A proteomic approach to de¢ning Zn(II)-binding proteins in E. coli [322] has identi¢ed 10 proteins not previously known to interact with Zn(II). Whilst the techniques used to identify Zn(II)-binding proteins may shed light on the distribution of Zn(II) in the cell, it must be borne in mind that chemical and structural integrity may be compromised in proteins that have undergone the lengthy extraction and separation processes inherent in proteomic studies and this may destroy valid metal-binding sites or create conditional ion-binding sites.

11. Concluding remarks Zn(II) is involved in a wide variety of cellular processes and the maintenance of cellular Zn(II) status is essential for survival. Therefore, an improved understanding of Zn(II) acquisition, assimilation and metabolism is of great signi¢cance. Investigations carried out in prokaryotic organisms have characterised many mechanisms for ‘channelling’ Zn(II) ions, which include mechanisms for Zn(II) import, export and potential intracellular tra⁄cking by Zn(II) metallo-chaperones. Each metal ion has one or more low-a⁄nity uptake systems, which tend to have broad substrate speci¢city and import metal ions when they are freely available. Additionally, when the supply of metal ions is limited, high-a⁄nity systems have also been found. These systems are selective for their target metal ions and are tightly regulated according to metal ion requirements. The regulation of these systems by metal-responsive transcriptional regulators modulates expression of the genes encoding metal ion binding and/or transport proteins. Hence, metal ion homeostasis is maintained in conditions of either metal ion limitation or excess. As access to ‘genomic’ technologies increases and the range of bacterial genome sequences proliferates it is strikingly apparent that the number of gene products involved in, or a¡ected by, Zn(II) metabolism is far greater than ¢rst expected and this, perhaps, re£ects the importance of metal ions in biology.

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The future lies in the understanding of Zn(II) (metal ion) availability in the cell and the pathways by which these magical crumbs of structure and catalysis are sensed and ultimately targeted to appropriate cellular sites. It is our opinion that such endeavours will prove fruitful in understanding many fundamental processes in prokaryotes and some more complex but less important life forms !

Acknowledgements The work presented here was aided by the generous donation of unpublished information by Dr Chris Rensing (University of Tucson, AZ, USA). We are particularly indebted to Professor Nigel Brown (University of Birmingham, Birmingham, UK) and Professor John Kay for critical reading of this work prior to publication.

References [1] Failla, M.L. (1977) Zinc: Functions and transport in micro-organisms. In: Microorganisms and Minerals (Weinberg, E.D., Ed.), Vol. 3, pp. 151^214. Marcel Dekker, New York. [2] Beyersmann, D. and Schmidt, C. (1999) Zinc and metallothionein in mammalian cell cycle regulation. In: Metals and Genetics (Sarkar, B., Ed.), pp. 145^157. Kluwer Academic/Plenum Publishers, New York. [3] Hartwig, A., Mullenders, L.H.F., Asmuss, M., Benters, M. and Kruger, I. (1999) E¡ect of metal compounds on the function of zinc ¢nger proteins involved in DNA repair. In: Metals and Genetics (Sarkar, B., Ed.), pp. 159^169. Kluwer Academic/Plenum Publishers, New York. [4] Vallee, B.L. and Auld, D.S. (1990) Zinc coordination, function, and structure of zinc enzymes and other proteins. Biochemistry (Moscow) 29, 5647^5659. [5] Suhy, D.A. and O’Halloran, T.V. (1996) Metal responsive gene regulation and the zinc metalloregulatory model. In: Metal Ions in Biological Systems (Dekker, M., Ed.), Vol. 32, pp. 557^578. Basel, Switzerland. [6] Coleman, J.E. (1992) Zinc proteins : enzymes, storage proteins, transcription factors, and replication proteins. Annu. Rev. Biochem. 61, 897^946. [7] Chou, A.Y., Archdeacon, J. and Kado, C.I. (1998) Agrobacterium transcriptional regulator Ros is a prokaryotic zinc ¢nger protein that regulates the plant oncogene ipt. Proc. Natl. Acad. Sci. USA 95, 5293^5298. [8] Bird, A.J., Turner Cavet, J.S., Lakey, J.H. and Robinson, N.J. (1998) A carboxyl-terminal Cys/His(2)-type zinc-¢nger motif in DNA primase in£uences DNA content in Synechococcus PCC 7942. J. Biol. Chem. 273, 21246^21252. [9] Daniel, H. and Adibi, S.A. (1995) Selective e¡ect of zinc on the uphill transport of oligopeptides into kidney brush border membrane vesicles. FASEB J. 9, 1112^1117. [10] O’Halloran, T.V. (1993) Transition-metals in control of gene-expression. Science 261, 715^725. [11] Nies, D.H. (1999) Microbial heavy-metal resistance. Appl. Microbiol. Biotechnol. 51, 730^750. [12] Lippard, S.J. and Berg, J.M. (1994) Principles of Bioinorganic Chemistry. University Science Books, Mill Valley, CA. [13] Rensing, C., Ghosh, M. and Rosen, B.P. (1999) Families of softmetal-ion-transporting ATPases. J. Bacteriol. 181, 5891^5897.

Cyaan Magenta Geel Zwart

304

D.K. Blencowe, A.P. Morby / FEMS Microbiology Reviews 27 (2003) 291^311

[14] Williams, R.J.P. (1993) The copper and zinc triads in biology. In: The Chemistry of Copper and Zinc Triads (Welch, A.J. and Chapman, S.K., Eds.), pp. 1^11. The Royal Society of Chemistry, Cambridge. [15] Williams, R.J.P. (1987) The biochemistry of zinc. Polyhedron 6, 61^ 69. [16] Auld, D.S. (2001) Zinc coordination sphere in biochemical zinc sites. Biometals 14, 271^313. [17] Outten, C.E., Tobin, D.A., Penner-Hahn, J.E. and O’Halloran, T.V. (2001) Characterization of the metal receptor sites in Escherichia coli Zur, an ultrasensitive zinc(II) metalloregulatory protein. Biochemistry (Moscow) 40, 10417^10423. [18] Rosen, B.P. (1999) The role of e¥ux in bacterial resistance to soft metals and metalloids. Essays Biochem. 34, 1^15. [19] Ames, G.F. (1974) Resolution of bacterial proteins by polyacrylamide gel electrophoresis on slabs. Membrane, soluble, and periplasmic fractions. J. Biol. Chem. 249, 634^644. [20] Higgins, C.F. (1992) ABC transporters: from microorganisms to man. Annu. Rev. Cell Biol. 8, 67^113. [21] Schneider, E. and Hunke, S. (1998) ATP-binding-cassette (ABC) transport systems: Functional and structural aspects of the ATP-hydrolyzing subunits/domains. FEMS Microbiol. Rev. 22, 1^20. [22] Dintilhac, A., Alloing, G., Granadel, C. and Claverys, J.P. (1997) Competence and virulence of Streptococcus pneumoniae: Adc and PsaA mutants exhibit a requirement for Zn and Mn resulting from inactivation of putative ABC metal permeases. Mol. Microbiol. 25, 727^739. [23] Patzer, S.I. and Hantke, K. (1998) The ZnuABC high-a⁄nity zinc uptake system and its regulator zur in Escherichia coli. Mol. Microbiol. 28, 1199^1210. [24] Park, P.W., Senior, R.M., Gri⁄n, G.L., Broekelmann, T.J., Mudd, M.S. and Mecham, R.P. (1995) Binding and degradation of elastin by the staphylolytic enzyme lysostaphin. Int. J. Biochem. Cell Biol. 27, 139^146. [25] Bartsevich, V.V. and Pakrasi, H.B. (1995) Molecular identi¢cation of an ABC transporter complex for manganese: analysis of a cyanobacterial mutant strain impaired in the photosynthetic oxygen evolution process. EMBO J. 14, 1845^1853. [26] Scha¡er, S., Hantke, K. and Braun, V. (1985) Nucleotide sequence of the iron regulatory gene fur. Mol. Gen. Genet. 200, 110^113. [27] Outten, C.E. and O’Halloran, T.V. (2001) Femtomolar sensitivity of metalloregulatory proteins controlling zinc homeostasis. Science 292, 2488^2492. [28] Patzer, S.I. and Hantke, K. (2000) The zinc-responsive regulator Zur and its control of the znu gene cluster encoding the ZnuABC zinc uptake system in Escherichia coli. J. Biol. Chem. 275, 24321^24332. [29] Morby, A.P., Turner, J.S., Huckle, J.W. and Robinson, N.J. (1993) SmtB is a metal-dependent repressor of the cyanobacterial metallothionein gene smtA: identi¢cation of a Zn inhibited DNA-protein complex. Nucleic Acids Res. 21, 921^925. [30] Erbe, J.L., Taylor, K.B. and Hall, L.M. (1995) Metalloregulation of the cyanobacterial smt locus: identi¢cation of SmtB binding sites and direct interaction with metals. Nucleic Acids Res. 23, 2472^2478. [31] Turner, J.S., Glands, P.D., Samson, A.C.R. and Robinson, N.J. (1996) Zn2þ -sensing by the cyanobacterial metallothionein repressor SmtB: di¡erent motifs mediate metal-induced protein-DNA dissociation. Nucleic Acids Res. 24, 3714^3721. [32] Dalet, K., Gouin, E., Cenatiempo, Y., Cossart, P. and Hechard, Y. (1999) Characterisation of a new operon encoding a Zur-like protein and an associated ABC zinc permease in Listeria monocytogenes. FEMS Microbiol. Lett. 174, 111^116. [33] Lu, D., Boyd, B. and Lingwood, C.A. (1997) Identi¢cation of the key protein for zinc uptake in Hemophilus in£uenzae. J. Biol. Chem. 272, 29033^29038. [34] Lu, D., Boyd, B. and Lingwood, C.A. (1998) The expression and characterization of a putative adhesin B from H. in£uenzae. FEMS Microbiol. Lett. 165, 129^137.

FEMSRE 774 2-6-03

[35] Lewis, D.A., Klesney-Tait, J., Lumbley, S.R., Ward, C.K., Latimer, J.L., Ison, C.A. and Hansen, E.J. (1999) Identi¢cation of the znuAencoded periplasmic zinc transport protein of Haemophilus ducreyi. Infect. Immun. 67, 5060^5068. [36] Dintilhac, A. and Claverys, J.P. (1997) The adc locus, which a¡ects competence for genetic transformation in Streptococcus pneumoniae, encodes an ABC transporter with a putative lipoprotein homologous to a family of streptococcal adhesins. Res. Microbiol. 148, 119^131. [37] Janulczyk, R., Pallon, J. and Bjorck, L. (1999) Identi¢cation and characterization of a Streptococcus pyogenes ABC transporter with multiple speci¢city for metal cations. Mol. Microbiol. 34, 596^606. [38] Lee, Y.H., Deka, R.K., Norgard, M.V., Radolf, J.D. and Hasemann, C.A. (1999) Treponema pallidum TroA is a periplasmic zinc-binding protein with a helical backbone. Nat. Struct. Biol. 6, 628^633. [39] Chen, C. and Morse, S.A. (2001) Identi¢cation and characterization of a high-a⁄nity zinc uptake system in Neisseria gonorrhoeae. FEMS Microbiol. Lett. 202, 67^71. [40] Gaballa, A. and Helmann, J.D. (1998) Identi¢cation of a zinc-speci¢c metalloregulatory protein, Zur, controlling zinc transport operons in Bacillus subtilis. J. Bacteriol. 180, 5815^5821. [41] Culotta, V.C., Lin, S.J., Schmidt, P., Klomp, L.W., Casareno, R.L. and Gitlin, J. (1999) Intracellular pathways of copper tra⁄cking in yeast and humans. Adv. Exp. Med. Biol. 448, 247^254. [42] Eide, D. (1997) Molecular biology of iron and zinc uptake in eukaryotes. Curr. Opin. Cell Biol. 9, 573^577. [43] Eide, D.J. (1998) The molecular biology of metal ion transport in Saccharomyces cerevisiae. Annu. Rev. Nutr. 18, 441^469. [44] Eide, D.J. (2000) Metal ion transport in eukaryotic microorganisms: insights from Saccharomyces cerevisiae. Adv. Microb. Physiol. 43, 1^ 38. [45] Eide, D.J. (2001) Functional genomics and metal metabloism. Gen. Biol. 2, 1028.1021^1028.1023. [46] Guerinot, M.L. and Eide, D. (1999) Zeroing in on zinc uptake in yeast and plants. Curr. Opin. Plant Biol. 2, 244^249. [47] Culotta, V.C., Liu, X.F. and Schmidt, P. (1999) The transport and intracellular tra⁄cking of metal ions in yeast. In: Metals and Genetics (Sarkar, B., Ed.), pp. 353^363. Kluwer Academic/Plenum Publishers, New York. [48] Cellier, M., Prive, G., Belouchi, A., Kwan, T., Rodrigues, V., Chia, W. and Gros, P. (1995) Nramp de¢nes a family of membrane proteins. Proc. Natl. Acad. Sci. USA 92, 10089^10093. [49] Vidal, S., Gros, P. and Skamene, E. (1995) Natural resistance to infection with intracellular parasites : molecular genetics identi¢es Nramp1 as the Bcg/Ity/Lsh locus. J. Leukoc. Biol. 58, 382^390. [50] Vidal, S.M., Malo, D., Vogan, K., Skamene, E. and Gros, P. (1993) Natural resistance to infection with intracellular parasites : isolation of a candidate for Bcg. Cell 73, 469^485. [51] Gunshin, H., Mackenzie, B., Berger, U.V., Gunshin, Y., Romero, M.F., Boron, W.F., Nussberger, S., Gollan, J.L. and Hediger, M.A. (1997) Cloning and characterization of a mammalian protoncoupled metal-ion transporter. Nature 388, 482^488. [52] Supek, F., Supekova, L., Nelson, H. and Nelson, N. (1997) Function of metal-ion homeostasis in the cell division cycle, mitochondrial protein processing, sensitivity to mycobacterial infection and brain function. J. Exp. Biol. 200, 321^330. [53] Supek, F., Supekova, L., Nelson, H. and Nelson, N. (1996) A yeast manganese transporter related to the macrophage protein involved in conferring resistance to mycobacteria. Proc. Natl. Acad. Sci. USA 93, 5105^5110. [54] Gruenheid, S., Cellier, M., Vidal, S. and Gros, P. (1995) Identi¢cation and characterization of a second mouse Nramp gene. Genomics 25, 514^525. [55] Vidal, S., Belouchi, A.M., Cellier, M., Beatty, B. and Gros, P. (1995) Cloning and characterization of a second human NRAMP gene on chromosome 12q13. Mamm. Genome 6, 224^230. [56] Pinner, E., Gruenheid, S., Raymond, M. and Gros, P. (1997) Functional complementation of the yeast divalent cation transporter fam-

Cyaan Magenta Geel Zwart

D.K. Blencowe, A.P. Morby / FEMS Microbiology Reviews 27 (2003) 291^311

[57]

[58]

[59] [60]

[61]

[62]

[63]

[64] [65] [66] [67] [68]

[69]

[70]

[71]

[72]

[73]

[74] [75]

[76]

[77]

[78]

ily SMF by NRAMP2, a member of the mammalian natural resistance-associated macrophage protein family. J. Biol. Chem. 272, 28933^28938. Liu, X.F., Supek, F., Nelson, N. and Culotta, V.C. (1997) Negative control of heavy metal uptake by the Saccharomyces cerevisiae BSD2 gene. J. Biol. Chem. 272, 11763^11769. Cellier, M., Belouchi, A. and Gros, P. (1996) Resistance to intracellular infections : comparative genomic analysis of Nramp. Trends Genet. 12, 201^204. Nelson, N. (1999) Metal ion transporters and homeostasis. EMBO J. 18, 4361^4371. Cellier, M.F., Bergevin, I., Boyer, E. and Richer, E. (2001) Polyphyletic origins of bacterial Nramp transporters. Trends Genet. 17, 365^ 370. Kehres, D.G., Zaharik, M.L., Finlay, B.B. and Maguire, M.E. (2000) The NRAMP proteins of Salmonella typhimurium and Escherichia coli are selective manganese transporters involved in the response to reactive oxygen. Mol. Microbiol. 36, 1085^1100. Makui, H., Roig, E., Cole, S.T., Helmann, J.D., Gros, P. and Cellier, M.F. (2000) Identi¢cation of the Escherichia coli K-12 Nramp orthologue (MntH) as a selective divalent metal ion transporter. Mol. Microbiol. 35, 1065^1078. Patzer, S.I. and Hantke, K. (2001) Dual repression by Fe2þ -Fur and Mn2þ -MntR of the mntH gene, encoding an NRAMP-like Mn2þ transporter in Escherichia coli. J. Bacteriol. 183, 4806^4813. Bhattacharyya, P. (1970) Active transport of manganese in isolated membranes of Escherichia coli. J. Bacteriol. 104, 1307^1311. Silver, S., Johnseine, P. and King, K. (1970) Manganses active transport in Escherichia coli. J. Bacteriol. 104, 1299^1306. Gaither, L.A. and Eide, D.J. (2001) Eukaryotic zinc transporters and their regulation. Biometals 14, 251^270. Guerinot, M.L. (2000) The ZIP family of metal transporters. Biochim. Biophys. Acta 1465, 190^198. Grass, G., Wong, M.D., Rosen, B.P., Smith, R.L. and Rensing, C. (2002) ZupT is a Zn(II) uptake system in Escherichia coli. J. Bacteriol. 184, 864^866. Eng, B.H., Guerinot, M.L., Eide, D. and Saier Jr., M.H. (1998) Sequence analyses and phylogenetic characterization of the ZIP family of metal ion transport proteins. J. Membr. Biol. 166, 1^7. Grotz, N., Fox, T., Connolly, E., Park, W., Guerinot, M.L. and Eide, D. (1998) Identi¢cation of a family of zinc transporter genes from Arabidopsis that respond to zinc de¢ciency. Proc. Natl. Acad. Sci. USA 95, 7220^7224. Korshunova, Y.O., Eide, D., Clark, W.G., Guerinot, M.L. and Pakrasi, H.B. (1999) The IRT1 protein from Arabidopsis thaliana is a metal transporter with a broad substrate range. Plant Mol. Biol. 40, 37^44. Costello, L.C., Liu, Y., Zou, J. and Franklin, R.B. (1999) Evidence for a zinc uptake transporter in human prostate cancer cells which is regulated by prolactin and testosterone. J. Biol. Chem. 274, 17499^ 17504. Gaither, L.A. and Eide, D.J. (2001) The human ZIP1 transporter mediates zinc uptake in human K562 erythroleukemia cells. J. Biol. Chem. 276, 22258^22264. Gaither, L.A. and Eide, D.J. (2000) Functional expression of the human hZIP2 zinc transporter. J. Biol. Chem. 275, 5560^5564. Zhao, H. and Eide, D. (1996) The ZRT2 gene encodes the low a⁄nity zinc transporter in Saccharomyces cerevisiae. J. Biol. Chem. 271, 23203^23210. Zhao, H. and Eide, D. (1996) The yeast ZRT1 gene encodes the zinc transporter protein of a high-a⁄nity uptake system induced by zinc limitation. Proc. Natl. Acad. Sci. USA 93, 2454^2458. Zhao, H. and Eide, D.J. (1997) Zap1p, a metalloregulatory protein involved in zinc-responsive transcriptional regulation in Saccharomyces cerevisiae. Mol. Cell. Biol. 17, 5044^5052. Jap, B.K. and Walian, P.J. (1996) Structure and functional mechanism of porins. Physiol. Rev. 76, 1073^1088.

FEMSRE 774 2-6-03

305

[79] Fajardo, D.A., Cheung, J., Ito, C., Sugawara, E., Nikaido, H. and Misra, R. (1998) Biochemistry and regulation of a novel Escherichia coli K-12 porin protein, OmpG, which produces unusually large channels. J. Bacteriol. 180, 4452^4459. [80] Igo, M.M., Slauch, J.M. and Silhavy, T.J. (1990) Signal transduction in bacteria : kinases that control gene expression. New Biol. 2, 5^9. [81] Elvin, C.M., Dixon, N.E. and Rosenberg, H. (1986) Molecular cloning of the phosphate (inorganic) transport (pit) gene of Escherichia coli K12. Identi¢cation of the pitþ gene product and physical mapping of the pit-gor region of the chromosome. Mol. Gen. Genet. 204, 477^484. [82] van Veen, H.W., Abee, T., Kortstee, G.J., Konings, W.N. and Zehnder, A.J. (1994) Translocation of metal phosphate via the phosphate inorganic transport system of Escherichia coli. Biochemistry (Moscow) 33, 1766^1770. [83] Bennett, R.L. and Malamy, M.H. (1970) Arsenate resistant mutants of Escherichia coli and phosphate transport. Biochem. Biophys. Res. Commun. 40, 496^503. [84] Beard, S.J., Hashim, R., Wu, G., Binet, M.R., Hughes, M.N. and Poole, R.K. (2000) Evidence for the transport of zinc(II) ions via the pit inorganic phosphate transport system in Escherichia coli. FEMS Microbiol. Lett. 184, 231^235. [85] Rosenberg, H., Gerdes, R.G. and Chegwidden, K. (1977) Two systems for the uptake of phosphate in Escherichia coli. J. Bacteriol. 131, 505^511. [86] Webb, M. (1970) Interrelationships between the utilisation of magnesium and the uptake of other bivalent cations by bacteria. Biochim. Biophys. Acta 222, 428^439. [87] Nelson, D.L. and Kennedy, E.P. (1971) Magnesium transport in Escherichia coli. Inhibition by cobaltous ion. J. Biol. Chem. 246, 3042^ 3049. [88] Jasper, P. and Silver, S. (1997) Magnesium transport in microorganisms. In: Microorganisms and Minerals (Weinberg, E.D., Ed.), Vol. 3, pp. 7^45. Marcel Dekker, New York. [89] Agrano¡, D.D. and Krishna, S. (1998) Metal ion homeostasis and intracellular parasitism. Mol. Microbiol. 28, 403^412. [90] Smith, R.L., Thompson, L.J. and Maguire, M.E. (1995) Cloning and characterization of MgtE, a putative new class of Mg2þ transporter from Bacillus ¢rmus OF4. J. Bacteriol. 177, 1233^1238. [91] Silver, S. (1969) Active transport of magnesium in Escherichia coli. Proc. Natl. Acad. Sci. USA 62, 764^771. [92] Lusk, J.E. and Kennedy, E.P. (1969) Magnesium transport in Escherichia coli. J. Biol. Chem. 244, 1653^1655. [93] Smith, R.L. and Maguire, M.E. (1995) Distribution of the CorA Mg2þ transport system in gram-negative bacteria. J. Bacteriol. 177, 1638^1640. [94] Townsend, D.E., Esenwine, A.J., George III, J., Bross, D., Maguire, M.E. and Smith, R.L. (1995) Cloning of the mgtE Mg2þ transporter from Providencia stuartii and the distribution of mgtE in Gram-negative and Gram-positive bacteria. J. Bacteriol. 177, 5350^5354. [95] MacDiarmid, C.W. and Gardner, R.C. (1998) Overexpression of the Saccharomyces cerevisiae magnesium transport system confers resistance to aluminum ion. J. Biol. Chem. 273, 1727^1732. [96] Nelson, D.L. and Kennedy, E.P. (1972) Transport of magnesium by a repressible and a nonrepressible system in Escherichia coli. Proc. Natl. Acad. Sci. USA 69, 1091^1093. [97] Park, M.H., Wong, B.B. and Lusk, J.E. (1976) Mutants in three genes a¡ecting transport of magnesium in Escherichia coli: genetics and physiology. J. Bacteriol. 126, 1096^1103. [98] Hmiel, S.P., Snavely, M.D., Florer, J.B., Maguire, M.E. and Miller, C.G. (1989) Magnesium transport in Salmonella typhimurium: genetic characterization and cloning of three magnesium transport loci. J. Bacteriol. 171, 4742^4751. [99] Snavely, M.D., Florer, J.B., Miller, C.G. and Maguire, M.E. (1989) Magnesium transport in Salmonella typhimurium : expression of cloned genes for three distinct Mg2þ transport systems. J. Bacteriol. 171, 4752^4760.

Cyaan Magenta Geel Zwart

306

D.K. Blencowe, A.P. Morby / FEMS Microbiology Reviews 27 (2003) 291^311

[100] Snavely, M.D., Florer, J.B., Miller, C.G. and Maguire, M.E. (1989) Magnesium transport in Salmonella typhimurium: 28 Mg2þ transport by the CorA, MgtA, and MgtB systems. J. Bacteriol. 171, 4761^ 4766. [101] Snavely, M.D., Miller, C.G. and Maguire, M.E. (1991) The mgtB Mg2þ transport locus of Salmonella typhimurium encodes a P-type ATPase. J. Biol. Chem. 266, 815^823. [102] Snavely, M.D., Gravina, S.A., Cheung, T.T., Miller, C.G. and Maguire, M.E. (1991) Magnesium transport in Salmonella typhimurium. Regulation of mgtA and mgtB expression. J. Biol. Chem. 266, 824^ 829. [103] Tao, T., Snavely, M.D., Farr, S.G. and Maguire, M.E. (1995) Magnesium transport in Salmonella typhimurium: mgtA encodes a P-type ATPase and is regulated by Mg2þ in a manner similar to that of the mgtB P-type ATPase. J. Bacteriol. 177, 2654^ 2662. [104] Tao, T., Grulich, P.F., Kucharski, L.M., Smith, R.L. and Maguire, M.E. (1998) Magnesium transport in Salmonella typhimurium : biphasic magnesium and time dependence of the transcription of the mgtA and mgtCB loci. Microbiology 144, 655^664. [105] Burland, V., Plunkett III, G., So¢a, H.J., Daniels, D.L. and Blattner, F.R. (1995) Analysis of the Escherichia coli genome VI: DNA sequence of the region from 92.8 through 100 minutes. Nucleic Acids Res. 23, 2105^2119. [106] Bachmann, B.J. (1990) Linkage map of Escherichia coli K-12, edition 8. Microbiol. Rev. 54, 130^197. [107] Bucheder, F. and Broda, E. (1974) Energy-dependent zinc transport by Escherichia coli. Eur. J. Biochem. 45, 555^559. [108] Nies, D.H. and Silver, S. (1989) Metal ion uptake by a plasmid-free metal-sensitive Alcaligenes eutrophus strain. J. Bacteriol. 171, 4073^ 4075. [109] Laddaga, R.A. and Silver, S. (1985) Cadmium uptake in Escherichia coli K-12. J. Bacteriol. 162, 1100^1105. [110] O’Halloran, T.V. and Culotta, V.C. (2000) Metallochaperones, an intracellular shuttle service for metal ions. J. Biol. Chem. 275, 25057^25060. [111] Valentine, J.S. and Gralla, E.B. (1997) Delivering copper inside yeast and human cells. Science 278, 817^818. [112] Klomp, L.W., Lin, S.J., Yuan, D.S., Klausner, R.D., Culotta, V.C. and Gitlin, J.D. (1997) Identi¢cation and functional expression of HAH1, a novel human gene involved in copper homeostasis. J. Biol. Chem. 272, 9221^9226. [113] Pufahl, R.A. and O’Halloran, T.V. (1999) Mechanisms of copper chaperone proteins. In: Metals and Genetics (Sarkar, B., Ed.), pp. 365^374. Kluwer Academic/Plenum Publishers, New York. [114] Poulos, T.L. (1999) Helping copper ¢nd a home. Nat. Struct. Biol. 6, 709^711. [115] Rosenzweig, A.C. and O’Halloran, T.V. (2000) Structure and chemistry of the copper chaperone proteins. Curr. Opin. Chem. Biol. 4, 140^147. [116] Rosenzweig, A.C. (2001) Copper delivery by metallochaperone proteins. Acc. Chem. Res. 34, 119^128. [117] Banci, L., Bertini, I., Del Conte, R., Markey, J. and Ruiz-Duenas, F.J. (2001) Copper tra⁄cking : the solution structure of Bacillus subtilis CopZ. Biochemistry (Moscow) 40, 15660^15668. [118] Cobine, P., Wickramasinghe, W.A., Harrison, M.D., Weber, T., Solioz, M. and Dameron, C.T. (1999) The Enterococcus hirae copper chaperone CopZ delivers copper(I) to the CopY repressor. FEBS Lett. 445, 27^30. [119] Wimmer, R., Herrmann, T., Solioz, M. and Wuthrich, K. (1999) NMR structure and metal interactions of the CopZ copper chaperone. J. Biol. Chem. 274, 22597^22603. [120] Daniels, M.J., Turner Cavet, J.S., Selkirk, R., Sun, H.Z., Parkinson, J.A., Sadler, P.J. and Robinson, N.J. (1998) Coordination of Zn2þ (and Cd2þ ) by prokaryotic metallothionein ^ Involvement of Hisimidazole. J. Biol. Chem. 273, 22957^22961. [121] Winge, D.R., Jensen, L.T. and Srinivasan, C. (1998) Metal-ion reg-

FEMSRE 774 2-6-03

[122] [123] [124]

[125]

[126] [127] [128] [129] [130]

[131]

[132]

[133]

[134]

[135]

[136]

[137]

[138] [139]

[140]

[141]

[142]

[143]

ulation of gene expression in yeast. Curr. Opin. Chem. Biol. 2, 216^ 221. Hamer, D.H. (1986) Metallothionein. Annu. Rev. Biochem. 55, 913^951. Kille, P., Hemmings, A. and Lunney, E.A. (1994) Memories of metallothionein. Biochim. Biophys. Acta 1205, 151^161. Klaassen, C.D., Liu, J. and Choudhuri, S. (1999) Metallothionein: An intracellular protein to protect against cadmium toxicity. Annu. Rev. Pharmacol. Toxicol. 39, 267^294. Nielson, K.B., Atkin, C.L. and Winge, D.R. (1985) Distinct metalbinding con¢gurations in metallothionein. J. Biol. Chem. 260, 5342^ 5350. Palmiter, R.D. (1987) Molecular biology of metallothionein gene expression. Experientia 52 (Suppl.), 63^80. Palmiter, R.D. (1998) The elusive function of metallothioneins. Proc. Natl. Acad. Sci. USA 95, 8428^8430. Vallee, B.L. (1987) Implications and inferences of metallothionein structure. Experientia 52 (Suppl.), 5^16. Vallee, B.L. (1995) The function of metallothionein. Neurochem. Int. 27, 23^33. Palmiter, R.D. and Findley, S.D. (1995) Cloning and functional characterization of a mammalian zinc transporter that confers resistance to zinc. EMBO J. 14, 639^649. Udom, A.O. and Brady, F.O. (1980) Reactivation in vitro of zincrequiring apo-enzymes by rat liver zinc-thionein. Biochem. J. 187, 329^335. Cano-Gauci, D.F. and Sarkar, B. (1996) Reversible zinc exchange between metallothionein and the estrogen receptor zinc ¢nger. FEBS Lett. 386, 1^4. Maret, W. (1994) Oxidative metal release from metallothionein via zinc-thiol/disul¢de interchange. Proc. Natl. Acad. Sci. USA 91, 237^ 241. Maret, W., Larsen, K.S. and Vallee, B.L. (1997) Coordination dynamics of biological zinc ‘clusters’ in metallothioneins and in the DNA-binding domain of the transcription factor Gal4. Proc. Natl. Acad. Sci. USA 94, 2233^2237. Jiang, L.J., Maret, W. and Vallee, B.L. (1998) The glutathione redox couple modulates zinc transfer from metallothionein to zinc-depleted sorbitol dehydrogenase. Proc. Natl. Acad. Sci. USA 95, 3483^3488. Zeng, J., Vallee, B.L. and Kagi, J.H. (1991) Zinc transfer from transcription factor IIIA ¢ngers to thionein clusters. Proc. Natl. Acad. Sci. USA 88, 9984^9988. Jacob, C., Maret, W. and Vallee, B.L. (1998) Control of zinc transfer between thionein, metallothionein, and zinc proteins. Proc. Natl. Acad. Sci. USA 95, 3489^3494. Jiang, L.J., Maret, W. and Vallee, B.L. (1998) The ATP-metallothionein complex. Proc. Natl. Acad. Sci. USA 95, 9146^9149. Zeng, J., Heuchel, R., Scha¡ner, W. and Kagi, J.H. (1991) Thionein (apometallothionein) can modulate DNA binding and transcription activation by zinc ¢nger containing factor Sp1. FEBS Lett. 279, 310^312. Ebadi, M., Iversen, P.L., Hao, R., Cerutis, D.R., Rojas, P., Happe, H.K., Murrin, L.C. and Pfei¡er, R.F. (1995) Expression and regulation of brain metallothionein. Neurochem. Int. 27, 1^22. Cousins, R.J. (1985) Absorption, transport, and hepatic metabolism of copper and zinc: special reference to metallothionein and ceruloplasmin. Physiol. Rev. 65, 238^309. Moltedo, O., Verde, C., Capasso, A., Parisi, E., Remondelli, P., Bonatti, S., Alvarez-Hernandez, X., Glass, J., Alvino, C.G. and Leone, A. (2000) Zinc transport and metallothionein secretion in the intestinal human cell line Caco-2. J. Biol. Chem. 275, 31819^ 31825. Morris, C.A., Nicolaus, B., Sampson, V., Harwood, J.L. and Kille, P. (1999) Identi¢cation and characterization of a recombinant metallothionein protein from a marine alga, Fucus vesiculosus. Biochem. J. 338, 553^560.

Cyaan Magenta Geel Zwart

D.K. Blencowe, A.P. Morby / FEMS Microbiology Reviews 27 (2003) 291^311 [144] Sturzenbaum, S.R., Kille, P. and Morgan, A.J. (1998) The identi¢cation, cloning and characterization of earthworm metallothionein. FEBS Lett. 431, 437^442. [145] Kille, P., Winge, D.R., Harwood, J.L. and Kay, J. (1991) A plant metallothionein produced in E. coli. FEBS Lett. 295, 171^175. [146] Tommey, A.M., Shi, J., Lindsay, W.P., Urwin, P.E. and Robinson, N.J. (1991) Expression of the pea gene PSMTA in E. coli. Metalbinding properties of the expressed protein. FEBS Lett. 292, 48^ 52. [147] Robinson, N.J., Evans, I.M., Mulcrone, J., Bryden, J. and Tommey, A.M. (1992) Genes with similarity to metallothionein genes and copper, zinc ligands in Pisum sativum L. Plant Soil 146, 291^298. [148] Higham, D.P., Sadler, P.J. and Scawen, M.D. (1986) Cadmiumbinding proteins in Pseudomonas putida: pseudothioneins. Environ. Health Perspect. 65, 5^11. [149] Higham, D.P., Sadler, P.J. and Scawen, M.D. (1985) Cadmium resistance in Pseudomonas putida ^ growth and uptake of cadmium. J. Gen. Microbiol. 131, 2539^2544. [150] Higham, D.P., Sadler, P.J. and Scawen, M.D. (1984) Cadmium resistante Pseudomonas putida synthesizes novel cadmium proteins. Science 225, 1043^1046. [151] Khazaeli, M.B. and Mitra, R.S. (1981) Cadmium-binding component in Escherichia coli during accommodation to low levels of this ion. Appl. Environ. Microbiol. 41, 46^50. [152] Turner, J.S. and Robinson, N.J. (1995) Cyanobacterial metallothioneins : Biochemistry and molecular genetics. J. Ind. Microbiol. 14, 119^125. [153] Blindauer, C.A., Harrison, M.D., Robinson, A.K., Parkinson, J.A., Bowness, P.W., Sadler, P.J. and Robinson, N.J. (2002) Multiple bacteria encode metallothioneins and SmtA-like zinc ¢ngers. Mol. Microbiol. 45, 1421^1432. [154] Shi, J., Lindsay, W.P., Huckle, J.W., Morby, A.P. and Robinson, N.J. (1992) Cyanabacterial metallothionein gene expressed in Escherichia coli metal-binding properties of the expressed protein. FEBS Lett. 303, 159^163. [155] Olafson, R.W., McCubbin, W.D. and Kay, C.M. (1988) Primaryand secondary-structural analysis of a unique prokaryotic metallothionein from a Synechoccus sp. cyanobacterium. Biochem. J. 251, 691^699. [156] Robinson, N.J., Gupta, A., Fordham-Skelton, A.P., Croy, R.R., Whitton, B.A. and Huckle, J.W. (1990) Prokaryotic metallothionein gene characterisation and expression : chromosome crawling by ligation-mediated PCR. Proc. R. Soc. Lond. B 242, 241^247. [157] Huckle, J.W., Morby, A.P., Turner, J.S. and Robinson, N.J. (1993) Isolation of a prokaryotic metallothionein locus and analysis of transcriptional control by trace metal ions. Mol. Microbiol. 7, 177^187. [158] Turner, J.S., Morby, A.P., Whitton, B.A., Gupta, A. and Robinson, N.J. (1993) Construction of Zn2þ /Cd2þ hypersensitive cyanobacterial mutants lacking a functional metallothionein locus. J. Biol. Chem. 268, 4494^4498. [159] Blindauer, C.A., Harrison, M.D., Parkinson, J.A., Robinson, A.K., Cavet, J.S., Robinson, N.J. and Sadler, P.J. (2001) A metallothionein containing a zinc ¢nger within a four-metal cluster protects a bacterium from zinc toxicity. Proc. Natl. Acad. Sci. USA 98, 9593^ 9598. [160] Cavet, J.S., Borrelly, G.P.M. and Robinson, N.J. (2003) Zn, Cu and Co in cyanobacteria: selective control of metal availability. FEMS Microbiol. Rev. 27, 165^181. [161] Olafson, R.W., Loya, S. and Sim, R.G. (1980) Physiological parameters of prokaryotic metallothionein induction. Biochem. Biophys. Res. Commun. 95, 1495^1503. [162] Shi, W., Wu, J. and Rosen, B.P. (1994) Identi¢cation of a putative metal binding site in a new family of metalloregulatory proteins. J. Biol. Chem. 269, 19826^19829. [163] Busenlehner, L.S., Pennella, M.A. and Giedroc, D.P. (2003) The SmtB/ArsR family of metalloregulatory transcriptional repressors:

FEMSRE 774 2-6-03

[164]

[165]

[166]

[167]

[168]

[169]

[170] [171]

[172]

[173]

[174]

[175]

[176]

[177]

[178]

[179]

[180] [181]

[182]

[183]

307

structural insights into prokaryotic metal resistance. FEMS Microbiol. Rev. 27, 131^143. Cook, W.J., Kar, S.R., Taylor, K.B. and Hall, L.M. (1998) Crystal structure of the cyanobacterial metallothionein repressor SmtB: A model for metalloregulatory proteins. J. Mol. Biol. 275, 337^346. Fleischmann, R.D., Adams, M.D., White, O., Clayton, R.A., Kirkness, E.F., Kerlavage, A.R., Bult, C.J., Tomb, J.F., Dougherty, B.A. and Merrick, J.M. et al. (1995) Whole-genome random sequencing and assembly of Haemophilus in£uenzae Rd. Science 269, 496^ 512. Noll, M., Petrukhin, K. and Lutsenko, S. (1998) Identi¢cation of a novel transcription regulator from Proteus mirabilis, PMTR, revealed a possible role of YJAI protein in balancing zinc in Escherichia coli. J. Biol. Chem. 273, 21393^21401. Hagenmaier, S., Stierhof, Y.D. and Henning, U. (1997) A new periplasmic protein of Escherichia coli which is synthesized in spheroplasts but not in intact cells. J. Bacteriol. 179, 2073^2076. Leonhartsberger, S., Huber, A., Lottspeich, F. and Bock, A. (2001) The hydH/G genes from Escherichia coli code for a zinc and lead responsive two-component regulatory system. J. Mol. Biol. 307, 93^ 105. Binet, M.R., Cruz-Ramos, H., Laver, J., Hughes, M.N. and Poole, R.K. (2002) Nitric oxide releases intracellular zinc from prokaryotic metallothionein in Escherichia coli. FEMS Microbiol. Lett. 213, 121^126. Pedersen, P.L. and Carafoli, E. (1987) Ion Motive ATPases. 2. Energy coupling and work output. Trends Biochem. Sci. 12, 186^189. Pedersen, P.L. and Carafoli, E. (1987) Ion motive ATPases. 1. Ubiquity, properties, and signi¢cance to cell-function. Trends Biochem. Sci. 12, 146^150. Axelsen, K.B. and Palmgren, M.G. (1998) Evolution of substrate speci¢cities in the P-type ATPase superfamily. J. Mol. Evol. 46, 84^ 101. Solioz, M. and Vulpe, C. (1996) CPx-type ATPases : A class of p-type ATPases that pump heavy metals. Trends Biochem. Sci. 21, 237^241. Lutsenko, S. and Kaplan, J.H. (1995) Organization of P-Type ATPases ^ Signi¢cance of structural diversity. Biochemistry (Moscow) 34, 15607^15613. Nucifora, G., Chu, L., Misra, T.K. and Silver, S. (1989) Cadmium resistance from Staphlococcus aureus plasmid pI258 cadA gene results from a cadmium-e¥ux ATPase. Proc. Natl. Acad. Sci. USA 86, 3544^3548. Tsai, K.-J., Yoon, K.P. and Lynn, A.R. (1992) ATP-dependent cadmium transport by the cadA cadmium resistance determinant in everted membrane vesicles of Bacillus subtilis. J. Bacteriol. 174, 116^121. Odermatt, A., Suter, H., Krapf, R. and Solioz, M. (1993) Primary structure of two P-type ATPases involved in copper homeostasis in Enterococcus hirae. J. Biol. Chem. 268, 12775^12779. Odermatt, A. and Solioz, M. (1995) Two trans-acting metalloregulatory proteins controlling expression of the copper-ATPases of Enterococcus hirae. J. Biol. Chem. 270, 4349^4354. Rensing, C., Fan, B., Sharma, R., Mitra, B. and Rosen, B.P. (2000) CopA: An Escherichia coli Cu(I)-translocating P-type ATPase. Proc. Natl. Acad. Sci. USA 97, 652^656. Solioz, M. and Stoyanov, J.V. (2003) Copper homeostasis in Enteroccocus hirae. FEMS Microbiol. Rev. 27, 185^195. Bull, P.C. and Cox, D.W. (1994) Wilson disease and Menkes disease : New handles on heavy-metal transport. Trends Genet. 10, 246^252. Yamaguchi, Y., Heiny, M.E., Suzuki, M. and Gitlin, J.D. (1996) Biochemical characterization and intracellular localization of the Menkes disease protein. Proc. Natl. Acad. Sci. USA 93, 14030^ 14035. Vulpe, C., Levinson, B., Whitney, S., Packman, S. and Gitschier, J. (1993) Isolation of a candidate gene for Menkes disease and evi-

Cyaan Magenta Geel Zwart

308

[184]

[185]

[186]

[187]

[188]

[189]

[190]

[191]

[192] [193]

[194]

[195]

[196]

[197]

[198] [199]

[200]

[201] [202]

D.K. Blencowe, A.P. Morby / FEMS Microbiology Reviews 27 (2003) 291^311 dence that it encodes a copper-transporting ATPase. Nat. Genet. 3, 7^13. Tanzi, R.E., Petrukhin, K., Chernov, I., Pellequer, J.L., Wasco, W., Ross, B., Romano, D.M., Parano, E., Pavone, L. and Brzustowicz, L.M. et al. (1993) The Wilson disease gene is a copper transporting ATPase with homology to the Menkes disease gene. Nat. Genet. 5, 344^350. Bull, P.C., Thomas, G.R., Rommens, J.M., Forbes, J.R. and Cox, D.W. (1993) The Wilson disease gene is a putative copper transporting P-type ATPase similar to the Menkes gene. Nat. Genet. 5, 327^337. Mercer, J.F., Livingston, J., Hall, B., Paynter, J.A., Begy, C., Chandrasekharappa, S., Lockhart, P., Grimes, A., Bhave, M. and Siemieniak, D. et al. (1993) Isolation of a partial candidate gene for Menkes disease by positional cloning. Nat. Genet. 3, 20^25. Gupta, A., Matsui, K., Lo, J.F. and Silver, S. (1999) Molecular basis for resistance to silver cations in Salmonella. Nat. Med. 5, 183^188. Rutherford, J.C., Cavet, J.S. and Robinson, N.J. (1999) Cobalt-dependent transcriptional switching by a dual-e¡ector MerR-like protein regulates a cobalt-exporting variant CPx-type ATPase. J. Biol. Chem. 274, 25827^25832. Borremans, B., Hobman, J.L., Provoost, A., Brown, N.L. and van Der Lelie, D. (2001) Cloning and functional analysis of the pbr lead resistance determinant of Ralstonia metallidurans CH34. J. Bacteriol. 183, 5651^5658. Mergeay, M., Monchy, S., Vallaeys, T., Auquier, V., Benotmane, A., Bertin, P., Taghavi, S., Dunn, J., van der Lelie, D. and Wattiez, R. (2003) Ralstonia metallidurans, a bacterium speci¢cally adapted to toxic metals: towards a tentative catalogue of metal-responsive genes. FEMS Microbiol. Rev. 27, 385^410. Tsai, K.J. and Linet, A.L. (1993) Formation of a phosphorylated enzyme intermediate by the CadA Cd2þ -ATPase. Arch. Biochem. Biophys. 305, 267^270. Solioz, M. and Camakaris, J. (1997) Acylphosphate formation by the Menkes copper ATPase. FEBS Lett. 412, 165^168. Melchers, K., Weitzenegger, T., Buhmann, A., Steinhilber, W., Sachs, G. and Schafer, K.P. (1996) Cloning and membrane topology of a P type ATPase from Helicobacter pylori. J. Biol. Chem. 271, 446^457. Moller, J.V., Juul, B. and le Maire, M. (1996) Structural organization, ion transport, and energy transduction of P-type ATPases. Biochim. Biophys. Acta 1286, 1^51. Gitschier, J., Mo¡at, B., Reilly, D., Wood, W.I. and Fairbrother, W.J. (1998) Solution structure of the fourth metal-binding domain from the Menkes copper-transporting ATPase. Nat. Struct. Biol. 5, 47^54. Smith, K. and Novick, R.P. (1972) Genetic studies on plasmidlinked cadmium resistance in Staphlococcus aureus. J. Bacteriol. 112, 761^772. Silver, S., Nucifora, G., Chu, L. and Misra, T.K. (1989) Bacterial resistance ATPases : primary pumps for exporting toxic cations and anions. Trends Biochem. Sci. 14, 76^80. Novick, R.P. and Roth, C. (1968) Plasmid-linked resistance to inorganic salts in Staphlococcus aureus. J. Bacteriol. 95, 1335^1342. Yoon, K.P. and Silver, S. (1991) A second gene in the Staphlococcus aureus cadA cadmium resistance determinant of plasmid pI258. J. Bacteriol. 173, 7636^7642. Yoon, K.P., Misra, T.K. and Silver, S. (1991) Regulation of the cadA cadmium resistance determinant of Staphlococcus aureus plasmid pI258. J. Bacteriol. 173, 7643^7649. Rensing, C., Sun, Y., Mitra, B. and Rosen, B.P. (1998) Pb(II)-translocating P-type ATPases. J. Biol. Chem. 273, 32614^32617. Tsai, K.J., Lin, Y.F., Wong, M.D., Yang, H.H., Fu, H.L. and Rosen, B.P. (2002) Membrane topology of the p1258 CadA Cd(II)/Pb(II)/Zn(II)-translocating P-type ATPase. J. Bioenerg. Biomembr. 34, 147^156.

FEMSRE 774 2-6-03

[203] Melchers, K., Schuhmacher, A., Buhmann, A., Weitzenegger, T., Belin, D., Grau, S. and Ehrmann, M. (1999) Membrane topology of CadA homologous P-type ATPase of Helicobacter pylori as determined by expression of phoA fusions in Escherichia coli and the positive inside rule. Res. Microbiol. 150, 507^520. [204] Melchers, K., Herrmann, L., Mauch, F., Bayle, D., Heuermann, D., Weitzenegger, T., Schuhmacher, A., Sachs, G., Haas, R., Bode, G., Bensch, K. and Schafer, K.P. (1998) Properties and function of the P type ion pumps cloned from Helicobacter pylori. Acta Physiol. Scand. 643 (Suppl.), 123^135. [205] Tynecka, Z., Gos, Z. and Zajac, J. (1981) Energy-dependent e¥ux of cadmium coded by a plasmid resistance determinant in Staphylococcus aureus. J. Bacteriol. 147, 313^319. [206] Wu, J. and Rosen, B.P. (1991) The ArsR protein is a trans-acting regulatory protein. Mol. Microbiol. 5, 1331^1336. [207] San Francisco, M.J., Hope, C.L., Owolabi, J.B., Tisa, L.S. and Rosen, B.P. (1990) Identi¢cation of the metalloregulatory element of the plasmid-encoded arsenical resistance operon. Nucleic Acids Res. 18, 619^624. [208] Xu, C. and Rosen, B.P. (1997) Dimerization is essential for DNA binding and repression by the ArsR metalloregulatory protein of Escherichia coli. J. Biol. Chem. 272, 15734^15738. [209] Endo, G. and Silver, S. (1995) CadC, the transcriptional regulatory protein of the cadmium resistance system of Staphlococcus aureus plasmid pI258. J. Bacteriol. 177, 4437^4441. [210] Sun, Y., Wong, M.D. and Rosen, B.P. (2001) Role of cysteinyl residues in sensing Pb(II), Cd(II), and Zn(II) by the plasmid pI258 CadC repressor. J. Biol. Chem. 276, 14955^14960. [211] Corbisier, P., Ji, G., Nuyts, G., Mergeay, M. and Silver, S. (1993) luxAB gene fusions with the arsenic and cadmium resistance operons of Staphylococcus aureus plasmid pI258. FEMS Microbiol. Lett. 110, 231^238. [212] Tauriainen, S., Karp, M., Chang, W. and Virta, M. (1998) Luminescent bacterial sensor for cadmium and lead. Biosens. Bioelectron. 13, 931^938. [213] Busenlehner, L.S., Cosper, N.J., Scott, R.A., Rosen, B.P., Wong, M.D. and Giedroc, D.P. (2001) Spectroscopic properties of the metalloregulatory Cd(II) and Pb(II) sites of S. aureus pI258 CadC. Biochemistry (Moscow) 40, 4426^4436. [214] Xu, C. and Rosen, B.P. (1999) Metalloregulation of soft metal resistance pumps. In: Metals and Genetics (Sarkar, B., Ed.), pp. 5^19. Kluwer Academic/Plenum Publishers, New York. [215] Ivey, D.M., Gu¡anti, A.A., Shen, Z., Kudyan, N. and Krulwich, T.A. (1992) The cadC gene product of alkaliphilic Bacillus ¢rmus OF4 partially restores Naþ resistance to an Escherichia coli strain lacking an Naþ /Hþ antiporter (NhaA). J. Bacteriol. 174, 4878^4884. [216] Lebrun, M., Audurier, A. and Cossart, P. (1994) Plasmid-borne cadmium resistance genes in Listeria monocytogenes are similar to cadA and cadC of Staphylococcus aureus and are induced by cadmium. J. Bacteriol. 176, 3040^3048. [217] Liu, C.Q., Khunajakr, N., Chia, L.G., Deng, Y.M., Charoenchai, P. and Dunn, N.W. (1997) Genetic analysis of regions involved in replication and cadmium resistance of the plasmid pND302 from Lactococcus lactis. Plasmid 38, 79^90. [218] Oger, C., Berthe, T., Quillet, L., Barray, S., Chi¡oleau, J.F. and Petit, F. (2001) Estimation of the abundance of the cadmium resistance gene cadA in microbial communities in polluted estuary water. Res. Microbiol. 152, 671^678. [219] Chopra, I. (1975) Mechanism of plasmid-mediated resistance to cadmium in Staphlococcus aureus. Antimicrob. Agents Chemother. 7, 8^14. [220] Novick, R.P., Murphy, E., Gryczan, T.J., Baron, E. and Edelman, I. (1979) Penicillinase plasmids of Staphylococcus aureus: restrictiondeletion maps. Plasmid 2, 109^129. [221] Bayle, D., Wangler, S., Weitzenegger, T., Steinhilber, W., Volz, J., Przybylski, M., Schafer, K.P., Sachs, G. and Melchers, K. (1998)

Cyaan Magenta Geel Zwart

D.K. Blencowe, A.P. Morby / FEMS Microbiology Reviews 27 (2003) 291^311

[222]

[223]

[224]

[225]

[226]

[227]

[228]

[229]

[230]

[231]

[232]

[233]

[234]

[235]

[236]

[237]

[238]

Properties of the P-type ATPases encoded by the copAP operons of Helicobacter pylori and Helicobacter felis. J. Bacteriol. 180, 317^329. Herrmann, L., Schwan, D., Garner, R., Mobley, H.L.T., Haas, R., Schafer, K.P. and Melchers, K. (1999) Helicobacter pylori cadA encodes an essential Cd(II)-Zn(II)-Co(II) resistance factor in£uencing urease activity. Mol. Microbiol. 33, 524^536. Volz, J., Bosch, F.U., Wunderlin, M., Schuhmacher, M., Melchers, K., Bensch, K., Steinhilber, W., Schafer, K.P., Toth, G., Penke, B. and Przybylski, M. (1998) Molecular characterization of metal-binding polypeptide domains by electrospray ionization mass spectrometry and metal chelate a⁄nity chromatography. J. Chromatogr. Agents 800, 29^37. Chaouni, L.B., Etienne, J., Greenland, T. and Vandenesch, F. (1996) Nucleic acid sequence and a⁄liation of pLUG10, a novel cadmium resistance plasmid from Staphylococcus lugdunensis. Plasmid 36, 1^8. Poitevin-Later, F., Vandenesch, F., Dyke, K., Fleurette, J. and Etienne, J. (1992) Cadmium-resistance plasmid in Staphylococcus lugdunensis. FEMS Microbiol. Lett. 78, 59^63. Crupper, S.S., Worrell, V., Stewart, G.C. and Iandolo, J.J. (1999) Cloning and expression of cadD, a new cadmium resistance gene of Staphylococcus aureus. J. Bacteriol. 181, 4071^4075. Udo, E.E., Jacob, L.E. and Mathew, B. (2000) A cadmium resistance plasmid, pXU5, in Staphylococcus aureus, strain ATCC25923. FEMS Microbiol. Lett. 189, 79^80. Horitsu, H., Yamamoto, K., Wachi, S., Kawai, K. and Fukuchi, A. (1986) Plasmid-determined cadmium resistance in Pseudomonas putida GAM-1 isolated from soil. J. Bacteriol. 165, 334^335. Lebrun, M., Loulergue, J., Chaslus-Dancla, E. and Audurier, A. (1992) Plasmids in Listeria monocytogenes in relation to cadmium resistance. Appl. Environ. Microbiol. 58, 3183^3186. Bal, N., Mintz, E., Guillain, F. and Catty, P. (2001) A possible regulatory role for the metal-binding domain of CadA, the Listeria monocytogenes Cd2þ -ATPase. FEBS Lett. 506, 249^252. Alonso, A., Sanchez, P. and Martinez, J.L. (2000) Stenotrophomonas maltophilia D457R contains a cluster of genes from gram-positive bacteria involved in antibiotic and heavy metal resistance. Antimicrob. Agents Chemother. 44, 1778^1782. Lee, S.W., Glickmann, E. and Cooksey, D.A. (2001) Chromosomal locus for cadmium resistance in Pseudomonas putida consisting of a cadmium-transporting ATPase and a MerR family response regulator. Appl. Environ. Microbiol. 67, 1437^1444. Hassan, M.T., van der Lelie, D., Springael, D., Romling, U., Ahmed, N. and Mergeay, M. (1999) Identi¢cation of a gene cluster, czr, involved in cadmium and zinc resistance in Pseudomonas aeruginosa. Gene 238, 417^425. Kaneko, T., Sato, S., Kotani, H., Tanaka, A., Asamizu, E., Nakamura, Y., Miyajima, N., Hirosawa, M., Sugiura, M., Sasamoto, S., Kimura, T., Hosouchi, T., Matsuno, A., Muraki, A., Nakazaki, N., Naruo, K., Okumura, S., Shimpo, S., Takeuchi, C., Wada, T., Watanabe, A., Yamada, M., Yasuda, M. and Tabata, S. (1996) Sequence analysis of the genome of the unicellular cyanobacterium Synechocystis sp. strain PCC6803. II. Sequence determination of the entire genome and assignment of potential protein-coding regions. DNA Res. 3, 109^136. Thelwell, C., Robinson, N.J. and TurnerCavet, J.S. (1998) An SmtB-like repressor from Synechocystis PCC 6803 regulates a zinc exporter. Proc. Natl. Acad. Sci. USA 95, 10728^10733. Rensing, C. and Grass, G. (2003) Escherichia coli mechanism of copper homeostasis in a changing environment. FEMS Microbiol. Rev. 27, 197^213. Blencowe, D.K., Marshall, S.J. and Morby, A.P. (1997) Preliminary characterisation of zntA, a gene which encodes a Zn(II)/Cd(II)-export protein in Escherichia coli. Biotechnol. et al. 2, 1^6. Rensing, C., Mitra, B. and Rosen, B.P. (1997) The zntA gene of Escherichia coli encodes a Zn(II)-translocating P-type ATPase. Proc. Natl. Acad. Sci. USA 94, 14326^14331.

FEMSRE 774 2-6-03

309

[239] Beard, S.J., Hashim, R., Membriool-Hernandez, J., Hughes, M.N. and Poole, R.K. (1997) Zinc(II) tolerence in Escherichia coli K-12: evidence that the zntA gene (o732) encodes a cation transport ATPase. Mol. Microbiol. 25, 883^891. [240] So¢a, H.J., Burland, V., Daniels, D.L., Plunkett III, G. and Blattner, F.R. (1994) Analysis of the Escherichia coli genome. V. DNA sequence of the region from 76.0^81.5 min. Nucleic Acids Res. 22, 2576^2586. [241] Sambongi, Y., Wakabayashi, T., Yoshimizu, T., Omote, H., Oka, T. and Futai, M. (1997) Caenorhabditis elegans cDNA for a Menkes/ Wilson disease gene homologue and its function in a yeast CCC2 gene deletion mutant. J. Biochem. (Tokyo) 121, 1169^1175. [242] Solioz, M. and Odermatt, A. (1995) Copper and silver transport by CopB-ATPase in membrane vesicles of Enterococcus hirae. J. Biol. Chem. 270, 9217^9221. [243] Ge, Z., Hiratsuka, K. and Taylor, D.E. (1995) Nucleotide sequence and mutational analysis indicate that two Helicobacter pylori genes encode a P-type ATPase and a cation-binding protein associated with copper transport. Mol. Microbiol. 15, 97^106. [244] Ge, Z. and Taylor, D.E. (1996) Helicobacter pylori genes hpcopA and hpcopP constitute a cop operon involved in copper export. FEMS Microbiol. Lett. 145, 181^188. [245] Fu, D., Beeler, T.J. and Dunn, T.M. (1995) Sequence, mapping and disruption of CCC2, a gene that cross-complements the Ca2þ -sensitive phenotype of csg1 mutants and encodes a P-type ATPase belonging to the Cu2þ -ATPase subfamily. Yeast 11, 283^292. [246] Kanamaru, K., Kashiwagi, S. and Mizuno, T. (1994) A coppertransporting P-type ATPase found in the thylakoid membrane of the cyanobacterium Synechococcus species PCC7942. Mol. Microbiol. 13, 369^377. [247] Phung, L.T., Ajlani, G. and Haselkorn, R. (1994) P-Type ATPase from the cyanobacterium Synechococcus-7942 related to the human Menkes and Wilson disease gene-products. Proc. Natl. Acad. Sci. USA 91, 9651^9654. [248] Rensing, C., Mitra, B. and Rosen, B.P. (1998) A Zn(II)-translocating P-type ATPase from Proteus mirabilis. Biochem. Cell. Biol. 76, 787^790. [249] Blencowe, D.K. (2002) Zn(II) Metabolism in Escherichia coli. Cardi¡ School of Biosciences (2), Cardi¡ University, Cardi¡. [250] Okkeri, J. and Haltia, T. (1999) Expression and mutagenesis of ZntA, a zinc-transporting P-type ATPase from Escherichia coli. Biochemistry (Moscow) 38, 14109^14116. [251] Sharma, R., Rensing, C., Rosen, B.P. and Mitra, B. (2000) The ATP hydrolytic activity of puri¢ed ZntA, a Pb(II)/Cd(II)/Zn(II)-translocating ATPase from Escherichia coli. J. Biol. Chem. 275, 3873^ 3878. [252] Banci, L., Bertini, I., Cio¢-Ba¡oni, S., D’Onofrio, M., Gonnelli, L., Marhuenda-Egea, F.C. and Ruiz-Duenas, F.J. (2002) Solution structure of the N-terminal domain of a potential copper-translocating P-type ATPase from Bacillus subtilis in the apo and Cu(I) loaded states. J. Mol. Biol. 317, 415^429. [253] Banci, L., Bertini, I., Cio¢-Ba¡oni, S., Finney, L.A., Outten, C.E. and O’Halloran, T.V. (2002) A new zinc-protein coordination site in intracellular metal tra⁄cking: solution structure of the Apo and Zn(II) forms of ZntA(46^118). J. Mol. Biol. 323, 883^897. [254] Konings, W.N., Kaback, H.R. and Lolkema, J.S. (1996) Transport Processes in Eukaryotic and Prokaryotic Organisms. Elsevier Science, Amsterdam. [255] Fan, B., Grass, G., Rensing, C. and Rosen, B.P. (2001) Escherichia coli CopA N-terminal Cys(X)(2)Cys motifs are not required for copper resistance or transport. Biochem. Biophys. Res. Commun. 286, 414^418. [256] Chelly, J., Tumer, Z., Tonnesen, T., Petterson, A., Ishikawa-Brush, Y., Tommerup, N., Horn, N. and Monaco, A.P. (1993) Isolation of a candidate gene for Menkes disease that encodes a potential heavy metal binding protein. Nat. Genet. 3, 14^19. [257] Yamaguchi, Y., Heiny, M.E. and Gitlin, J.D. (1993) Isolation and

Cyaan Magenta Geel Zwart

310

[258]

[259]

[260]

[261]

[262]

[263] [264]

[265]

[266] [267] [268] [269]

[270]

[271]

[272]

[273] [274] [275]

[276]

[277]

[278]

[279]

D.K. Blencowe, A.P. Morby / FEMS Microbiology Reviews 27 (2003) 291^311 characterization of a human liver cDNA as a candidate gene for Wilson disease. Biochem. Biophys. Res. Commun. 197, 271^277. Thomas, G.R., Forbes, J.R., Roberts, E.A., Walshe, J.M. and Cox, D.W. (1995) The Wilson disease gene: spectrum of mutations and their consequences. Nat. Genet. 9, 210^217. Brocklehurst, K.R., Hobman, J.L., Lawley, B., Blank, L., Marshall, S.J., Brown, N.L. and Morby, A.P. (1999) ZntR is a Zn(II)-responsive MerR-like transcriptional regulator of zntA in Escherichia coli. Mol. Microbiol. 31, 893^902. Christie, G.E., White, T.J. and Goodwin, T.S. (1994) A MerR homolog at 74 minutes on the Escherichia coli genome. Gene 146, 131^ 132. Binet, M.R. and Poole, R.K. (2000) Cd(II), Pb(II) and Zn(II) ions regulate expression of the metal-transporting P-type ATPase ZntA in Escherichia coli. FEBS Lett. 473, 67^70. Brown, N.L., Camakaris, J., Lee, B.T.O., Williams, T., Morby, A.P., Parkhill, J. and Rouch, D.A. (1991) Bacterial resistances to mercury and copper. J. Cell Biochem. 46, 106^114. Brown, N.L. (1985) Bacterial resistance to mercury ^ Reductio ad absurdum. Trends Biochem. Sci. 10, 400^403. Frantz, B. and O’Halloran, T.V. (1990) DNA distortion accompanies transcriptional activation by the metal-responsive gene-regulatory protein MerR. Biochemistry (Moscow) 29, 4747^4751. Ralston, D.M. and O’Halloran, T.V. (1990) Ultrasensitivity and heavy-metal selectivity of the allosterically modulated MerR transcription complex. Proc. Natl. Acad. Sci. USA 87, 3846^3850. Summers, A.O. (1986) Organization, expression, and evolution of genes for mercury resistance. Annu. Rev. Microbiol. 40, 607^634. Summers, A.O. (1992) Untwist and shout: a heavy metal-responsive transcriptional regulator. J. Bacteriol. 174, 3097^3101. Silver, S. and Misra, T.K. (1988) Plasmid mediated heavy metal resistances. Annu. Rev. Microbiol. 42, 717^743. Mindlin, S., Kholodii, G., Gorlenko, Z., Minakhina, S., Minakhin, L., Kalyaeva, E., Kopteva, A., Petrova, M., Yurieva, O. and Nikiforov, V. (2001) Mercury resistance transposons of gram-negative environmental bacteria and their classi¢cation. Res. Microbiol. 152, 811^822. Brown, N.L., Stoyanov, J.V., Kidd, S.P. and Hobman, J.L. (2003) The MerR family of transcriptional regulators. FEMS Microbiol. Rev. 27, 145^163. Outten, C.E., Outten, F.W. and O’Halloran, T.V. (1999) DNA distortion mechanism for transcriptional activation by ZntR, a Zn(II)responsive MerR homologue in Escherichia coli. J. Biol. Chem. 274, 37517^37524. Lund, P.A., Ford, S.J. and Brown, N.L. (1986) Transcriptional regulation of the mercury-resistance genes of transposon Tn501. J. Gen. Microbiol. 132, 465^480. Hobman, J.L. and Brown, N.L. (1997) Bacterial mercury-resistance genes. Metal Ions Biol. Syst. 34, 527^568. Harley, C.B. and Reynolds, R.P. (1987) Analysis of E. coli promoter sequences. Nucleic Acids Res. 15, 2343^2361. de Haseth, P.L., Zupancic, M.L. and Record Jr., M.T. (1998) RNA polymerase-promoter interactions : the comings and goings of RNA polymerase. J. Bacteriol. 180, 3019^3025. Ansari, A.Z., Chael, M.L. and O’Halloran, T.V. (1992) Allosteric underwinding of DNA is a critical step in positive control of transcription by Hg-MerR. Nature 355, 87^89. Ansari, A.Z., Bradner, J.E. and O’Halloran, T.V. (1995) DNA-bend modulation in a repressor-to-activator switching mechanism. Nature 374, 371^375. Schultz, S.C., Shields, G.C. and Steitz, T.A. (1991) Crystal structure of a CAP-DNA complex: the DNA is bent by 90 degrees. Science 253, 1001^1007. O’Halloran, T.V., Frantz, B., Shin, M.K., Ralston, D.M. and Wright, J.G. (1989) The MerR heavy metal receptor mediates positive activation in a topologically novel transcription complex. Cell 56, 119^129.

FEMSRE 774 2-6-03

[280] Heltzel, A., Lee, I.W., Totis, P.A. and Summers, A.O. (1990) Activator-dependent preinduction binding of sigma-70 RNA polymerase at the metal-regulated mer promoter. Biochemistry (Moscow) 29, 9572^9584. [281] Hidalgo, E., Bollinger Jr., J.M., Bradley, T.M., Walsh, C.T. and Demple, B. (1995) Binuclear [2Fe-2S] clusters in the Escherichia coli SoxR protein and role of the metal centers in transcription. J. Biol. Chem. 270, 20908^20914. [282] Hitomi, Y., Outten, C.E. and O’Halloran, T.V. (2001) Extreme zincbinding thermodynamics of the metal sensor/regulator protein, ZntR. J. Am. Chem. Soc. 123, 8614^8615. [283] Brim, H., Heyndrickx, M., de Vos, P., Wilmotte, A., Springael, D., Schlegel, H.G. and Mergeay, M. (1999) Ampli¢ed rDNA restriction analysis and further genotypic characterisation of metal-resistant soil bacteria and related facultative hydrogenotrophs. Syst. Appl. Microbiol. 22, 258^268. [284] Mergeay, M., Nies, D., Schlegel, H.G., Gerits, J., Charles, P. and Van Gijsegem, F. (1985) Alcaligenes eutrophus CH34 is a facultative chemolithotroph with plasmid-bound resistance to heavy metals. J. Bacteriol. 162, 328^334. [285] Mergeay, M., Houba, C. and Gerits, J. (1978) Extrachromosomal inheritance controlling resistance to cadmium, cobalt, copper and zinc ions : evidence from curing in a Pseudomonas. Arch. Int. Physiol. Biochem. 86, 440^442. [286] Dressler, C., Kues, U., Nies, D.H. and Friedrich, B. (1991) Determinants encoding resistance to several heavy metals in newly isolated copper-resistant bacteria. Appl. Environ. Microbiol. 57, 3079^ 3085. [287] Diels, D. and Mergeay, M. (1990) DNA probe-mediated detection of resistant bacteria from soils highly poluted by heavy metals. Appl. Environ. Microbiol. 56, 1485^1491. [288] Yabuuchi, E., Kosako, Y., Yano, I., Hotta, H. and Nishiuchi, Y. (1995) Transfer of two Burkholderia and an Alcaligenes species to Ralstonia gen. nov. Proposal of Ralstonia pickettii (Ralston, Palleroni and Doudoro¡ 1973) comb. nov., Ralstonia solanacearum (Smith 1896) comb. nov. and Ralstonia eutropha (Davis 1969) comb. nov. Microbiol. Immunol. 39, 897^904. [289] Taghavi, S., Mergeay, M., Nies, D. and van der Lelie, D. (1997) Alcaligenes eutrophus as a model system for bacterial interactions with heavy metals in the environment. Res. Microbiol. 148, 536^551. [290] Nies, D.H., Mergeay, M., Friedrich, B. and Schlegel, H.G. (1987) Cloning of plasmid genes encoding resistance to cadmium, zinc, and cobalt in Alcaligenes eutrophus CH34. J. Bacteriol. 169, 4865^4868. [291] Diels, L., Faelen, M., Mergeay, M. and Nies, D.H. (1985) Mercury transposons from plasmids governing multiple resistance to heavey metals in Alcaligenes eutrophus CH34. Arch. Int. Physiol. Biochem. 93, B27^B28. [292] Taghavi, S., Mergeay, M. and van der Lelie, D. (1997) Genetic and physical maps of the Alcaligenes eutrophus CH34 megaplasmid pMOL28 and its derivative pMOL50 obtained after temperatureinduced mutagenesis and mortality. Plasmid 37, 22^34. [293] Nies, A., Nies, D.H. and Silver, S. (1989) Cloning and expression of plasmid genes encoding resistances to chromate and cobalt in Alcaligenes eutrophus. J. Bacteriol. 171, 5065^5070. [294] Nies, D.H. and Silver, S. (1989) Plasmid-determined inducible e¥ux is responsible for resistance to cadmium, zinc, and cobalt in Alcaligenes eutrophus. J. Bacteriol. 171, 896^900. [295] Nies, A., Nies, D.H. and Silver, S. (1990) Nucleotide sequence and expression of a plasmid-encoded chromate resistance determinant from Alcaligenes eutrophus. J. Biol. Chem. 265, 5648^5653. [296] Liesegang, H., Lemke, K., Siddiqui, R.A. and Schlegel, H.-G. (1993) Characterisation of the inducible nickle and cobalt resistance determinant cnr from pMOL28 of Alcaligenes eutrophus CH34. J. Bacteriol. 175, 767^778. [297] Colland, J.M., Corbisier, P., Diels, L., Dong, Q., Jeanthon, C., Mergeay, M., Taghavi, S., van der Lelie, D., Wilmotte, A. and Wuertz, S. (1994) Plasmids for heavy metal resistance in Alcaligenes

Cyaan Magenta Geel Zwart

D.K. Blencowe, A.P. Morby / FEMS Microbiology Reviews 27 (2003) 291^311

[298]

[299]

[300]

[301]

[302]

[303] [304] [305]

[306] [307]

[308] [309] [310] [311]

[312]

[313]

[314]

[315]

eutrophus CH34: Mechanisms and applications. FEMS Microbiol. Rev. 14, 405^414. Dong, Q. and Mergeay, M. (1994) Czc/cnr e¥ux: a three-component chemiosmotic antiport pathway with a 12-transmembrane-helix protein. Mol. Microbiol. 14, 185^187. Siddiqui, R.A., Benthin, K. and Schlegel, H.G. (1989) Cloning of pMOL28-encoded nickel resistance genes and expression of the genes in Alcaligenes eutrophus and Pseudomonas spp. J. Bacteriol. 171, 5071^5078. Collard, J.M., Provoost, A., Taghavi, S. and Mergeay, M. (1993) A new type of Alcaligenes eutrophus CH34 zinc resistance generated by mutations a¡ecting regulation of the cnr cobalt-nickel resistance system. J. Bacteriol. 175, 779^784. Sensfuss, C. and Schlegal, H.G. (1988) Plasmid pMOL28-encoded resistance to nickel is due to speci¢c e¥ux. FEMS Microbiol. Lett. 55, 295^298. Nies, D.H., Nies, A., Chu, L. and Silver, S. (1989) Expression and nucleotide sequence of a plasmid-determined divalent cation e¥ux system from Alcaligenes eutrophus. Proc. Natl. Acad. Sci. USA 86, 7351^7355. Nies, D.H. (1992) Resistance to cadmium, cobalt, zinc, and nickel in microbes. Plasmid 27, 17^28. Nies, D.H. and Silver, S. (1995) Ion e¥ux systems involved in bacterial metal resistances. J. Ind. Microbiol. 14, 186^199. Diels, L., Dong, Q., van der Lelie, D., Baeyens, W. and Mergeay, M. (1995) The czc operon of Alcaligenes eutrophus CH34: from resistance mechanism to the removal of heavy metals. J. Ind. Microbiol. 14, 142^153. Silver, S. (1996) Bacterial resistances to toxic metal ions ^ A review. Gene 179, 9^19. Saier Jr., M.H., Tam, R., Reizer, A. and Reizer, J. (1994) Two novel families of bacterial membrane proteins concerned with nodulation, cell division and transport. Mol. Microbiol. 11, 841^847. Silver, S. and Phung, L.T. (1996) Bacterial heavy metal resistance: New surprises. Annu. Rev. Microbiol. 50, 753^789. Nikaido, H. (1996) Multidrug e¥ux pumps of gram-negative bacteria. J. Bacteriol. 178, 5853^5859. Saris, N.-E.L. and Niva, K. (1994) Is Zn2þ transported by the mitochondrial calcium uniporter? FEBS Lett. 356, 195^198. Kunito, T., Kusano, T., Oyaizu, H., Senoo, K., Kanazawa, S. and Matsumoto, S. (1996) Cloning and sequence analysis of czc genes in Alcaligenes sp. strain CT14. Biosci. Biotechnol. Biochem. 60, 699^ 704. Kuroda, M., Hayashi, H. and Ohta, T. (1999) Chromosome-determined zinc-responsible operon czr in Staphylococcus aureus strain 912. Microbiol. Immunol. 43, 115^125. Xiong, A. and Jayaswall, R.K. (1998) Molecular characterisation of a chromosomal determinant confering resistance to zinc and cobalt ions in Staphylococcus aureus. J. Bacteriol. 180, 4024^4029. McClain, M.S., Hurley, M.C., Brieland, J.K. and Engleberg, N.C. (1996) The Legionella pneumophila hel locus encodes intracellularly induced homologs of heavy-metal ion transporters of Alcaligenes spp. Infect. Immun. 64, 1532^1540. Nies, D.H. (2003) E¥ux-mediated heavy metal resistance in prokaryotes. FEMS Microbiol. Rev. 27, 313^339.

FEMSRE 774 2-6-03

311

[316] Paulsen, I.T. and Saier Jr., M.H. (1997) A novel family of ubiquitous heavy metal ion transport proteins. J. Membr. Biol. 156, 99^ 103. [317] Singh, V.K., Xiong, A., Usgaard, T.R., Chakrabarti, S., Deora, R., Misra, T.K. and Jayaswal, R.K. (1999) ZntR is an autoregulatory protein and negatively regulates the chromosomal zinc resistance operon znt of Staphylococcus aureus. Mol. Microbiol. 33, 200^ 207. [318] Grass, G., Fan, B., Rosen, B.P., Franke, S., Nies, D.H. and Rensing, C. (2001) ZitB (YbgR), a member of the cation di¡usion facilitator family, is an additional zinc transporter in Escherichia coli. J. Bacteriol. 183, 4664^4667. [319] Lee, S.M., Grass, G., Haney, C.J., Fan, B., Rosen, B.P., Anton, A., Nies, D.H. and Rensing, C. (2002) Functional analysis of the Escherichia coli zinc transporter ZitB. FEMS Microbiol. Lett. 215, 273^278. [320] Worlock, A.J. and Smith, R.L. (2002) ZntB is a novel Zn2þ transporter in Salmonella enterica serovar Typhimurium. J. Bacteriol. 184, 4369^4373. [321] Brocklehurst, K.R. and Morby, A.P. (2000) Metal-ion tolerance in Escherichia coli : analysis of transcriptional pro¢les by gene-array technology. Microbiology 146, 2277^2282. [322] Katayama, A., Tsujii, A., Wada, A., Nishino, T. and Ishihama, A. (2002) Systematic search for zinc-binding proteins in Escherichia coli. Eur. J. Biochem. 269, 2403^2413. [323] Brown, N.L., Ford, S.J., Pridmore, R.D. and Fritzinger, D.C. (1983) Nucleotide sequence of a gene from the Pseudomonas transposon Tn501 encoding mercuric reductase. Biochemistry (Moscow) 22, 4089^4095. [324] Brown, N.L., Misra, T.K., Winnie, J.N., Schmidt, A., Sei¡, M. and Silver, S. (1986) The nucleotide sequence of the mercuric resistance operons of plasmid R100 and transposon Tn501: further evidence for mer genes which enhance the activity of the mercuric ion detoxi¢cation system. Mol. Gen. Genet. 202, 143^151. [325] Lund, P.A. and Brown, N.L. (1987) Role of the merT and merP gene products of transposon Tn501 in the induction and expression of resistance to mercuric ions. Gene 52, 207^214. [326] Lutsenko, S., Petrukhin, K., Cooper, M.J., Gilliam, C.T. and Kaplan, J.H. (1997) N-terminal domains of human copper-transporting adenosine triphosphatases (the Wilson’s and Menkes disease proteins) bind copper selectively in vivo and in vitro with stoichiometry of one copper per metal-binding repeat. J. Biol. Chem. 272, 18939^ 18944. [327] Pufahl, R.A., Singer, C.P., Peariso, K.L., Lin, S.J., Schmidt, P.J., Fahrni, C.J., Culotta, V.C., PennerHahn, J.E. and Ohalloran, T.V. (1997) Metal ion chaperone function of the soluble Cu(I) receptor Atx1. Science 278, 853^856. [328] Steele, R.A. and Opella, S.J. (1997) Structures of the reduced and mercury-bound forms of MerP, the periplasmic protein from the bacterial mercury detoxi¢cation system. Biochemistry (Moscow) 36, 6885^6895. [329] Qian, H., Sahlman, L., Eriksson, P.O., Hambraeus, C., Edlund, U. and Sethson, I. (1998) NMR solution structure of the oxidized form of MerP, a mercuric ion binding protein involved in bacterial mercuric ion resistance. Biochemistry (Moscow) 37, 9316^9322.

Cyaan Magenta Geel Zwart