Two Menkes-type atpases supply copper for photosynthesis in Synechocystis PCC 6803

Nitrogen-dependent luteolin effect on Microcystis growth and microcystin-pollution risk - Novel mechanism insights unveiled by comparative proteomics and gene expression

Phytogenic allelochemical luteolin has potential to mitigate Microcystis-dominated cyanobacterial blooms (MCBs), but its algicidal effect against toxigenic Microcystis may be impacted by natural factors, especially nitrogen (N) level in waters. This study innovatively explored N-dependent effect of luteolin on Microcystis growth and its microcystins (MCs) production/release, and elucidated underlying mechanisms from proteomics and gene expression views. Generally, at each N level, rising luteolin dose progressively inhibited Microcystis growth by inhibiting proteins syntheses and genes expression involving light-capturing, photosynthetic electron transfer, Calvin cycle and phosphorus (P) acquisition, according to comparative proteomics and gene expression. At higher luteolin dose and lower N level, Microcystis cell tended to increase microcystins (MCs) production and conservation ability, with the highest increase degree observed at 12 mg/L luteolin and 0.5 mg/L N on day 10, reaching 1.96 and 2.68 folds of luteolin-free control, respectively, but decrease MC-release as extracellular MCs content (EMC), with inhibition ratio of 72.86%, 73.57%, 74.45% and 40.58%, 45.28%, 60.00% at rising N level under 12 mg/L luteolin stress on day 10 and 16, respectively. These enabled cellular defensive response of Microcystis to stronger stress and N limitation. Under luteolin stress, higher N level more strongly up-regulated numerous processes (e.g., oxidoreductase activity, ATP binding and transmembrane transport, oxidative phosphorylation, tricarboxylic acid cycle, fatty acid biosynthesis, glycolysis/gluconeogenesis, pyruvate, amino acids metabolism, metal ion-binding, P acquisition) as compensative protective responses to progressively down-regulated photosynthetic and ribosomal processes at higher N level, thus causing faster Microcystis growth than lower N level. This study provided novel insights for N-dependent effect and mechanisms of luteolin on MCBs mitigation and MCs risk control, and guided algicidal application of luteolin in different eutrophic-degree waters.

Copper Homeostatic Mechanisms and Their Role in the Virulence of Escherichia coli and Salmonella enterica

Copper is an essential micronutrient that also exerts toxic effects at high concentrations. This review summarizes the current state of knowledge on copper handling and homeostasis systems in Escherichia coli and Salmonella enterica. We describe the mechanisms by which transcriptional regulators, efflux pumps, detoxification enzymes, metallochaperones, and ancillary copper response systems orchestrate cellular response to copper stress. E. coli and S. enterica are important pathogens of humans and animals. We discuss the critical role of copper during killing of these pathogens by macrophages and in nutritional immunity at the bacterial-pathogen-host interface. In closing, we identify opportunities to advance our understanding of the biological roles of copper in these model enteric bacterial pathogens.

A protease-mediated mechanism regulates the cytochrome c 6/plastocyanin switch in Synechocystis sp. PCC 6803

After the Great Oxidation Event (GOE), iron availability was greatly decreased, and photosynthetic organisms evolved several alternative proteins and mechanisms. One of these proteins, plastocyanin, is a type I blue-copper protein that can replace cytochrome c ₆ as a soluble electron carrier between cytochrome b ₆ f and photosystem I. In most cyanobacteria, expression of these two alternative proteins is regulated by copper availability, but the regulatory system remains unknown. Herein, we provide evidence that the regulatory system is composed of a BlaI/CopY-family transcription factor (PetR) and a BlaR-membrane protease (PetP). PetR represses petE (plastocyanin) expression and activates petJ (cytochrome c ₆), while PetP controls PetR levels in vivo. Using whole-cell extracts, we demonstrated that PetR degradation requires both PetP and copper. Transcriptomic analysis revealed that the PetRP system regulates only four genes (petE, petJ, slr0601, and slr0602), highlighting its specificity. Furthermore, the presence of petE and petRP in early branching cyanobacteria indicates that acquisition of these genes could represent an early adaptation to decreased iron bioavailability following the GOE.

Current knowledge and recent advances in understanding metabolism of the model cyanobacterium Synechocystis sp. PCC 6803

Cyanobacteria are key organisms in the global ecosystem, useful models for studying metabolic and physiological processes conserved in photosynthetic organisms, and potential renewable platforms for production of chemicals. Characterizing cyanobacterial metabolism and physiology is key to understanding their role in the environment and unlocking their potential for biotechnology applications. Many aspects of cyanobacterial biology differ from heterotrophic bacteria. For example, most cyanobacteria incorporate a series of internal thylakoid membranes where both oxygenic photosynthesis and respiration occur, while CO2 fixation takes place in specialized compartments termed carboxysomes. In this review, we provide a comprehensive summary of our knowledge on cyanobacterial physiology and the pathways in Synechocystis sp. PCC 6803 (Synechocystis) involved in biosynthesis of sugar-based metabolites, amino acids, nucleotides, lipids, cofactors, vitamins, isoprenoids, pigments and cell wall components, in addition to the proteins involved in metabolite transport. While some pathways are conserved between model cyanobacteria, such as Synechocystis, and model heterotrophic bacteria like Escherichia coli, many enzymes and/or pathways involved in the biosynthesis of key metabolites in cyanobacteria have not been completely characterized. These include pathways required for biosynthesis of chorismate and membrane lipids, nucleotides, several amino acids, vitamins and cofactors, and isoprenoids such as plastoquinone, carotenoids, and tocopherols. Moreover, our understanding of photorespiration, lipopolysaccharide assembly and transport, and degradation of lipids, sucrose, most vitamins and amino acids, and haem, is incomplete. We discuss tools that may aid our understanding of cyanobacterial metabolism, notably CyanoSource, a barcoded library of targeted Synechocystis mutants, which will significantly accelerate characterization of individual proteins.

Adaptive laboratory evolution of the fast-growing cyanobacterium Synechococcus elongatus PCC 11801 for improved solvent tolerance

Cyanobacteria hold promise as cell factories for the photoautotrophic conversion of carbon dioxide to useful chemicals. For the eventual commercial viability of such processes, cyanobacteria need to be engineered for (i) efficient channeling of carbon flux toward the product of interest and (ii) improved product tolerance, the latter being the focus of this study. We chose the recently reported, fast-growing, high light and CO₂ tolerant cyanobacterium Synechococcus elongatus PCC 11801 for adaptive laboratory evolution. In two parallel experiments that lasted over 8400 h of culturing and 100 serial passages, S. elongatus PCC 11801 was evolved to tolerate 5 g/L n-butanol or 30 g/L 2,3-butanediol representing a 100% improvement in concentrations tolerated. The evolved strains retained alcohol tolerance even after being passaged several times without the alcohol stress suggesting that the changes were permanent. Whole genome sequencing of the n-butanol evolved strains revealed mutations in a number of stress responsive genes encoding translation initiation factors, RpoB and an ABC transporter. In 2,3-butanediol evolved strains, genes for ClpC, a different ABC transporter, glyceraldehyde-3-phosphate dehydrogenase and phosphoribulokinase were found to be mutated. Furthermore, the evolved strains showed significant improvement in tolerance toward several other alcohols. Notably, the n-butanol evolved strain could tolerate up to 32 g/L ethanol, thereby making it a promising host for photosynthetic production of biofuels via metabolic engineering.

Staphylococcus aureus lacking a functional MntABC manganese import system has increased resistance to copper

S. aureus USA300 isolates utilize the copBL and copAZ gene products to prevent Cu intoxication. We created and examined a ΔcopAZ ΔcopBL mutant strain (cop-). The cop- strain was sensitive to Cu and accumulated intracellular Cu. We screened a transposon (Tn) mutant library in the cop- background and isolated strains with Tn insertions in the mntABC operon that permitted growth in the presence of Cu. The mutations were in mntA and they were recessive. Under the growth conditions utilized, MntABC functioned in manganese (Mn) import. When cultured with Cu, strains containing a mntA::Tn accumulated less Cu than the parent strain. Mn(II) supplementation improved growth when cop- was cultured with Cu and this phenotype was dependent upon the presence of MntR, which is a repressor of mntABC transcription. A ΔmntR strain had an increased Cu load and decreased growth in the presence of Cu, which was abrogated by the introduction of mntA::Tn. Over-expression of mntABC increased cellular Cu load and sensitivity to Cu. The presence of a mntA::Tn mutation protected iron-sulfur (FeS) enzymes from inactivation by Cu. The data presented are consistent with a model wherein defective MntABC results in decreased cellular Cu accumulation and protection to FeS enzymes from Cu poisoning.

Cu Homeostasis in Bacteria: The Ins and Outs

Copper (Cu) is an essential trace element for all living organisms and used as cofactor in key enzymes of important biological processes, such as aerobic respiration or superoxide dismutation. However, due to its toxicity, cells have developed elaborate mechanisms for Cu homeostasis, which balance Cu supply for cuproprotein biogenesis with the need to remove excess Cu. This review summarizes our current knowledge on bacterial Cu homeostasis with a focus on Gram-negative bacteria and describes the multiple strategies that bacteria use for uptake, storage and export of Cu. We furthermore describe general mechanistic principles that aid the bacterial response to toxic Cu concentrations and illustrate dedicated Cu relay systems that facilitate Cu delivery for cuproenzyme biogenesis. Progress in understanding how bacteria avoid Cu poisoning while maintaining a certain Cu quota for cell proliferation is of particular importance for microbial pathogens because Cu is utilized by the host immune system for attenuating pathogen survival in host cells.

Comparative and Functional Algal Genomics

Over 100 whole-genome sequences from algae are published or soon to be published. The rapidly increasing availability of these fundamental resources is changing how we understand one of the most diverse, complex, and understudied groups of photosynthetic eukaryotes. Genome sequences provide a window into the functional potential of individual algae, with phylogenomics and functional genomics as tools for contextualizing and transferring knowledge from reference organisms into less well-characterized systems. Remarkably, over half of the proteins encoded by algal genomes are of unknown function, highlighting the volume of functional capabilities yet to be discovered. In this review, we provide an overview of publicly available algal genomes, their associated protein inventories, and their quality, with a summary of the statuses of protein function understanding and predictions.

Metalloproteins in the Biology of Heterocysts

Cyanobacteria are photoautotrophic microorganisms present in almost all ecologically niches on Earth. They exist as single-cell or filamentous forms and the latter often contain specialized cells for N₂ fixation known as heterocysts. Heterocysts arise from photosynthetic active vegetative cells by multiple morphological and physiological rearrangements including the absence of O₂ evolution and CO₂ fixation. The key function of this cell type is carried out by the metalloprotein complex known as nitrogenase. Additionally, many other important processes in heterocysts also depend on metalloproteins. This leads to a high metal demand exceeding the one of other bacteria in content and concentration during heterocyst development and in mature heterocysts. This review provides an overview on the current knowledge of the transition metals and metalloproteins required by heterocysts in heterocyst-forming cyanobacteria. It discusses the molecular, physiological, and physicochemical properties of metalloproteins involved in N₂ fixation, H₂ metabolism, electron transport chains, oxidative stress management, storage, energy metabolism, and metabolic networks in the diazotrophic filament. This provides a detailed and comprehensive picture on the heterocyst demands for Fe, Cu, Mo, Ni, Mn, V, and Zn as cofactors for metalloproteins and highlights the importance of such metalloproteins for the biology of cyanobacterial heterocysts.

In vivo transposon tagging in the nonheterocystous nitrogen-fixing cyanobacterium Leptolyngbya boryana

Nitrogenase is an oxygen-vulnerable metalloenzyme that catalyzes nitrogen fixation. It largely remains unknown how nitrogenase coexists with oxygenic photosynthesis in nonheterocystous cyanobacteria, since there have been no appropriate model cyanobacteria so far. Here, we demonstrate in vivo transposon tagging in the nonheterocystous cyanobacterium Leptolyngbya boryana as a forward genetics approach. By conjugative transfer, a mini-Tn5-derived vector, pKUT-Tn5-Sm/Sp, was transferred from Escherichia coli to L. boryana cells. Of 1839 streptomycin-resistant colonies, we isolated three mutants showing aberrant diazotrophic growth. Genome resequencing identified the insertion sites of the transposon in the mutants. This in vivo transposon tagging mutagenesis of L. boryana provides a promising system to investigate molecular mechanisms to resolve the Oxygen Paradox between nitrogen fixation and oxygenic photosynthesis in cyanobacteria.

Bacterial Cu(+)-ATPases: models for molecular structure-function studies

The early discovery of the human Cu(+)-ATPases and their link to Menkes and Wilson's diseases brought attention to the unique role of these transporters in copper homeostasis. The characterization of bacterial Cu(+)-ATPases has significantly furthered our understanding of the structure, selectivity and transport mechanism of these enzymes, as well as their interplay with other elements of Cu(+) distribution networks. This review focuses on the structural-functional insights that have emerged from studies of bacterial Cu(+)-ATPases at the molecular level and how these observations have contributed to drawing up a comprehensive picture of cellular copper homeostasis.

Structural basis for copper/silver binding by theSynechocystismetallochaperone CopM

Copper homeostasis integrates multiple processes from sensing to storage and efflux out of the cell. CopM is a cyanobacterial metallochaperone, the gene for which is located upstream of a two-component system for copper resistance, but the molecular basis for copper recognition by this four-helical bundle protein is unknown. Here, crystal structures of CopM in apo, copper-bound and silver-bound forms are reported. Monovalent copper/silver ions are buried within the bundle core; divalent copper ions are found on the surface of the bundle. The monovalent copper/silver-binding site is constituted by two consecutive histidines and is conserved in a previously functionally unknown protein family. The structural analyses show two conformational states and suggest that flexibility in the first α-helix is related to the metallochaperone function. These results also reveal functional diversity from a protein family with a simple four-helical fold.

Uncovering the Transmembrane Metal Binding Site of the Novel Bacterial Major Facilitator Superfamily-Type Copper Importer CcoA

Uptake and trafficking of metals and their delivery to their respective metalloproteins are important processes. Cells need precise control of each step to avoid exposure to excessive metal concentrations and their harmful consequences. Copper (Cu) is a required micronutrient used as a cofactor in proteins. However, in large amounts, it can induce oxidative damage; hence, Cu homeostasis is indispensable for cell survival. Biogenesis of respiratory heme-Cu oxygen (HCO) reductases includes insertion of Cu into their catalytic subunits to form heme-Cu binuclear centers. Previously, we had shown that CcoA is a major facilitator superfamily (MFS)-type bacterial Cu importer required for biogenesis of cbb₃-type cytochrome c oxidase (cbb₃-Cox). Here, using Rhodobacter capsulatus, we focused on the import and delivery of Cu to cbb₃-Cox. By comparing the CcoA amino acid sequence with its homologues from other bacterial species, we located several well-conserved Met, His, and Tyr residues that might be important for Cu transport. We determined the topology of the transmembrane helices that carry these residues to establish that they are membrane embedded, and substituted for them amino acids that do not ligand metal atoms. Characterization of these mutants for their uptake of radioactive ⁶⁴Cu and cbb₃-Cox activities demonstrated that Met233 and His261 of CcoA are essential and Met237 and Met265 are important, whereas Tyr230 has no role for Cu uptake or cbb₃-Cox biogenesis. These findings show for the first time that CcoA-mediated Cu import relies on conserved Met and His residues that could act as metal ligands at the membrane-embedded Cu binding domain of this transporter.

Cu is a micronutrient that is both essential and toxic; hence, its cellular homeostasis is crucial. Respiratory cbb₃-type cytochrome c oxidases (cbb₃-Cox) are Cu-containing energy-transducing enzymes that are important for many microaerophilic processes, including photosynthesis, respiration, and bacterial pathogenesis. How Cu is incorporated into cbb₃-Cox enzymes is not well known. So far, CcoA is the only known major facilitator superfamily (MFS)-type transporter required for Cu import into the bacterial cytoplasm and for cbb₃-Cox biogenesis. This study shows that the membrane-embedded, universally conserved Met and His residues of CcoA are essential for its Cu import function and also for its role in cbb₃-Cox biogenesis, shedding light on the mechanism of function of this bacterial prototypical Cu importer.

Identification and characterization of the zosA gene involved in copper uptake in Bacillus subtilis 168

DL-Penicillamine, a copper-specific metal chelator, remarkably suppressed the growth of Bacillus subtilis 168 when added to a synthetic medium under Cu(2+) limitation. DNA microarray and screening of 2,602 knockout mutants showed that the zosA gene was de-repressed in the presence of 0.1% dl-penicillamine, and that the zosA mutant was sensitive to dl-penicillamine medium. The zosA mutant delayed the growth under Cu-limitation even without the chelator, and the sensitivity to dl-penicillamine was reversed by induction using 0.3 mM IPTG and the Pspac promoter inserted directly upstream of the zosA gene. Furthermore, the zosA mutant showed elevated tolerance of excessive Cu(2+) but not of excessive Zn(2+) added to LB and synthetic media. Homology modeling of the ZosA protein suggested that the protein can fold itself into essential domains for constituting a metal transporting ATPase. Our study suggests that zosA is a candidate gene involved in copper uptake.

Copper-transporting ATPases: The evolutionarily conserved machineries for balancing copper in living systems

Copper ATPases (Cu-ATPases) are ubiquitous transmembrane proteins using energy from ATP to transport copper across different biological membranes of prokaryotic and eukaryotic cells. As they belong to the P-ATPase family, Cu-ATPases contain a characteristic catalytic domain with an evolutionarily conserved aspartate residue phosphorylated by ATP to form a phosphoenzyme intermediate, as well as transmembrane helices containing a cation-binding cysteine-proline-cysteine/histidine/serine (CPx) motif for catalytic activation and cation translocation. In addition, most Cu-ATPases possess the N-terminal Cu-binding CxxC motif required for regulation of enzyme activity. In cells, the Cu-ATPases receive copper from soluble chaperones and maintain intracellular copper homeostasis by efflux of copper from the cell or transport of the metal into the intracellular compartments. In addition, copper pumps play an essential role in cuproprotein biosynthesis by the uptake of copper into the cell or delivery of the metal into the chloroplasts and thylakoid lumen or into the lumen of the secretory pathway, where the metal ion is incorporated into copper-dependent enzymes. In the recent years, significant progress has been made toward understanding the function and regulation of Cu-transporting ATPases in archaea, bacteria, yeast, humans, and plants, providing new insights into the specific physiological roles of these essential proteins in various organisms and revealing some conservative regulatory mechanisms of Cu-ATPase activity. In this review, the structural, biochemical, and functional properties of Cu-ATPases from phylogenetically different organisms are summarized and discussed, with particular attention given to the recent insights into the molecular biology of copper pumps in plants.

Structure and Function of Cu(I)- and Zn(II)-ATPases

Copper and zinc are micronutrients essential for the function of many enzymes while also being toxic at elevated concentrations. Cu(I)- and Zn(II)-transporting P-type ATPases of subclass 1B are of key importance for the homeostasis of these transition metals, allowing ion transport across cellular membranes at the expense of ATP. Recent biochemical studies and crystal structures have significantly improved our understanding of the transport mechanisms of these proteins, but many details about their structure and function remain elusive. Here we compare the Cu(I)- and Zn(II)-ATPases, scrutinizing the molecular differences that allow transport of these two distinct metal types, and discuss possible future directions of research in the field.

Functional and Biochemical Characterization of Cucumber Genes Encoding Two Copper ATPases CsHMA5.1 and CsHMA5.2

Plant copper P1B-type ATPases appear to be crucial for maintaining copper homeostasis within plant cells, but until now they have been studied mostly in model plant systems. Here, we present the molecular and biochemical characterization of two cucumber copper ATPases, CsHMA5.1 and CsHMA5.2, indicating a different function for HMA5-like proteins in different plants. When expressed in yeast, CsHMA5.1 and CsHMA5.2 localize to the vacuolar membrane and are activated by monovalent copper or silver ions and cysteine, showing different affinities to Cu(+) (Km ∼1 or 0.5 μM, respectively) and similar affinity to Ag(+) (Km ∼2.5 μM). Both proteins restore the growth of yeast mutants sensitive to copper excess and silver through intracellular copper sequestration, indicating that they contribute to copper and silver detoxification. Immunoblotting with specific antibodies revealed the presence of CsHMA5.1 and CsHMA5.2 in the tonoplast of cucumber cells. Interestingly, the root-specific CsHMA5.1 was not affected by copper stress, whereas the widely expressed CsHMA5.2 was up-regulated or down-regulated in roots upon copper excess or deficiency, respectively. The copper-induced increase in tonoplast CsHMA5.2 is consistent with the increased activity of ATP-dependent copper transport into tonoplast vesicles isolated from roots of plants grown under copper excess. These data identify CsHMA5.1 and CsHMA5.2 as high affinity Cu(+) transporters and suggest that CsHMA5.2 is responsible for the increased sequestration of copper in vacuoles of cucumber root cells under copper excess.

Copper Delivery to Chloroplast Proteins and its Regulation

Copper is required for photosynthesis in chloroplasts of plants because it is a cofactor of plastocyanin, an essential electron carrier in the thylakoid lumen. Other chloroplast copper proteins are copper/zinc superoxide dismutase and polyphenol oxidase, but these proteins seem to be dispensable under conditions of low copper supply when transcripts for these proteins undergo microRNA-mediated down regulation. Two ATP-driven copper transporters function in tandem to deliver copper to chloroplast compartments. This review seeks to summarize the mechanisms of copper delivery to chloroplast proteins and its regulation. We also delineate some of the unanswered questions that still remain in this field.

CopM is a novel copper-binding protein involved in copper resistance in Synechocystis sp. PCC 6803

Copper resistance system in the cyanobacterium Synechocystis sp. PCC 6803 comprises two operons, copMRS and copBAC, which are expressed in response to copper in the media. copBAC codes for a heavy-metal efflux–resistance nodulation and division (HME-RND) system, while copMRS codes for a protein of unknown function, CopM, and a two-component system CopRS, which controls the expression of these two operons. Here, we report that CopM is a periplasmic protein able to bind Cu(I) with high affinity (K_D ∼3 × 10⁻¹⁶). Mutants lacking copM showed a sensitive copper phenotype similar to mutants affected in copB, but lower than mutants of the two-component system CopRS, suggesting that CopBAC and CopM constitute two independent resistance mechanisms. Moreover, constitutive expression of copM is able to partially suppress the copper sensitivity of the copR mutant strain, pointing out that CopM per se is able to confer copper resistance. Furthermore, constitutive expression of copM was able to reduce total cellular copper content of the copR mutant to the levels determined in the wild-type (WT) strain. Finally, CopM was localized not only in the periplasm but also in the extracellular space, suggesting that CopM can also prevent copper accumulation probably by direct copper binding outside the cell.

Metals in cyanobacteria: analysis of the copper, nickel, cobalt and arsenic homeostasis mechanisms

Traces of metal are required for fundamental biochemical processes, such as photosynthesis and respiration. Cyanobacteria metal homeostasis acquires an important role because the photosynthetic machinery imposes a high demand for metals, making them a limiting factor for cyanobacteria, especially in the open oceans. On the other hand, in the last two centuries, the metal concentrations in marine environments and lake sediments have increased as a result of several industrial activities. In all cases, cells have to tightly regulate uptake to maintain their intracellular concentrations below toxic levels. Mechanisms to obtain metal under limiting conditions and to protect cells from an excess of metals are present in cyanobacteria. Understanding metal homeostasis in cyanobacteria and the proteins involved will help to evaluate the use of these microorganisms in metal bioremediation. Furthermore, it will also help to understand how metal availability impacts primary production in the oceans. In this review, we will focus on copper, nickel, cobalt and arsenic (a toxic metalloid) metabolism, which has been mainly analyzed in model cyanobacterium Synechocystis sp. PCC 6803.

Evolution of a plant-specific copper chaperone family for chloroplast copper homeostasis

Metallochaperones traffic copper (Cu(+)) from its point of entry at the plasma membrane to its destination. In plants, one destination is the chloroplast, which houses plastocyanin, a Cu-dependent electron transfer protein involved in photosynthesis. We present a previously unidentified Cu(+) chaperone that evolved early in the plant lineage by an alternative-splicing event of the pre-mRNA encoding the chloroplast P-type ATPase in Arabidopsis 1 (PAA1). In several land plants, recent duplication events created a separate chaperone-encoding gene coincident with loss of alternative splicing. The plant-specific Cu(+) chaperone delivers Cu(+) with specificity for PAA1, which is flipped in the envelope relative to prototypical bacterial ATPases, compatible with a role in Cu(+) import into the stroma and consistent with the canonical catalytic mechanism of these enzymes. The ubiquity of the chaperone suggests conservation of this Cu(+)-delivery mechanism and provides a unique snapshot into the evolution of a Cu(+) distribution pathway. We also provide evidence for an interaction between PAA2, the Cu(+)-ATPase in thylakoids, and the Cu(+)-chaperone for Cu/Zn superoxide dismutase (CCS), uncovering a Cu(+) network that has evolved to fine-tune Cu(+) distribution.

Metal ion homeostasis in Listeria monocytogenes and importance in host-pathogen interactions

Listeria monocytogenes is responsible for one of the most life-threatening food-borne infections and the leading cause of food-poisoning associated deaths in the UK. Infection may be of the unborn/newly born infant where disease may manifest as listeric abortion, stillbirth or late-onset neonatal listeriosis, while in adults, infection usually affects the central nervous system causing meningitis. Crucial to the survival of L. monocytogenes, both inside and outside the host, is its ability to acquire metals which act as cofactors for a broad range of its cellular proteins. However, L. monocytogenes must also protect itself against the innate toxicity of metals. The importance of metals in host-pathogen interactions is illustrated by the restriction of metals (including zinc and iron) in vertebrates in response to infection and the use of high levels of metals (copper and zinc) as part of the antimicrobial defences within host phagocytes. As such, L. monocytogenes is equipped with various mechanisms to tightly control its cellular metal pools and avoid metal poisoning. These include multiple DNA-binding metal-responsive transcription factors, metal-acquisition, metal-detoxification and metal-storage systems, some of which represent key L. monocytogenes virulence determinants. This review discusses current knowledge of the role of metals in L. monocytogenes infections, with a focus on the mechanisms that contribute to zinc and copper homeostasis in this organism. The requirement to precisely control cellular metal levels may impose a vulnerability to L. monocytogenes which can be exploited in antimicrobials and therapeutics.

Global transcriptional profiles of the copper responses in the cyanobacterium Synechocystis sp. PCC 6803

Copper is an essential element involved in fundamental processes like respiration and photosynthesis. However, it becomes toxic at high concentration, which has forced organisms to control its cellular concentration. We have recently described a copper resistance system in the cyanobacterium Synechocystis sp. PCC 6803, which is mediated by the two-component system, CopRS, a RND metal transport system, CopBAC and a protein of unknown function, CopM. Here, we report the transcriptional responses to copper additions at non-toxic (0.3 µM) and toxic concentrations (3 µM) in the wild type and in the copper sensitive copR mutant strain. While 0.3 µM copper slightly stimulated metabolism and promoted the exchange between cytochrome c6 and plastocyanin as soluble electron carriers, the addition of 3 µM copper catalyzed the formation of ROS, led to a general stress response and induced expression of Fe-S cluster biogenesis genes. According to this, a double mutant strain copRsufR, which expresses constitutively the sufBCDS operon, tolerated higher copper concentration than the copR mutant strain, suggesting that Fe-S clusters are direct targets of copper toxicity in Synechocystis. In addition we have also demonstrated that InrS, a nickel binding transcriptional repressor that belong to the CsoR family of transcriptional factor, was involved in heavy metal homeostasis, including copper, in Synechocystis. Finally, global gene expression analysis of the copR mutant strain suggested that CopRS only controls the expression of copMRS and copBAC operons in response to copper.

Origin and evolution of metal P-type ATPases in Plantae (Archaeplastida)

Metal ATPases are a subfamily of P-type ATPases involved in the transport of metal cations across biological membranes. They all share an architecture featuring eight transmembrane domains in pairs of two and are found in prokaryotes as well as in a variety of Eukaryotes. In Arabidopsis thaliana, eight metal P-type ATPases have been described, four being specific to copper transport and four displaying a broader metal specificity, including zinc, cadmium, and possibly copper and calcium. So far, few efforts have been devoted to elucidating the origin and evolution of these proteins in Eukaryotes. In this work, we use large-scale phylogenetics to show that metal P-type ATPases form a homogenous group among P-type ATPases and that their specialization into either monovalent (Cu) or divalent (Zn, Cd…) metal transport stems from a gene duplication that took place early in the evolution of Life. Then, we demonstrate that the four subgroups of plant metal ATPases all have a different evolutionary origin and a specific taxonomic distribution, only one tracing back to the cyanobacterial progenitor of the chloroplast. Finally, we examine the subsequent evolution of these proteins in green plants and conclude that the genes thoroughly characterized in model organisms are often the result of lineage-specific gene duplications, which calls for caution when attempting to infer function from sequence similarity alone in non-model organisms.

Differential roles for the Co(2+) /Ni(2+) transporting ATPases, CtpD and CtpJ, in Mycobacterium tuberculosis virulence

The genome of Mycobacterium tuberculosis encodes two paralogous P1 B 4 -ATPases, CtpD (Rv1469) and CtpJ (Rv3743). Both proteins showed ATPase activation by Co(2+) and Ni(2+) , and both appear to be required for metal efflux from the cell. However, using a combination of biochemical and genetic studies we found that these proteins play non-redundant roles in virulence and metal efflux. CtpJ expression is induced by Co(2+) and this protein possesses a relatively high turnover rate. A ctpJ deletion mutant accumulated Co(2+) , indicating that this ATPase controls cytoplasmic metal levels. In contrast, CtpD expression is induced by redox stressors and this protein displays a relatively low turnover rate. A ctpD mutant failed to accumulate metal, suggesting an alternative cellular function. ctpD is cotranscribed with two thioredoxin genes trxA (Rv1470), trxB (Rv1471), and an enoyl-coA hydratase (Rv1472), indicating a possible role for CtpD in the metallation of these redox-active proteins. Supporting this, in vitro metal binding assays showed that TrxA binds Co(2+) and Ni(2+) . Mutation of ctpD, but not ctpJ, reduced bacterial fitness in the mouse lung, suggesting that redox maintenance, but not Co(2+) accumulation, is important for growth in vivo.

Mechanisms of copper homeostasis in bacteria

Copper is an important micronutrient required as a redox co-factor in the catalytic centers of enzymes. However, free copper is a potential hazard because of its high chemical reactivity. Consequently, organisms exert a tight control on Cu(+) transport (entry-exit) and traffic through different compartments, ensuring the homeostasis required for cuproprotein synthesis and prevention of toxic effects. Recent studies based on biochemical, bioinformatics, and metalloproteomics approaches, reveal a highly regulated system of transcriptional regulators, soluble chaperones, membrane transporters, and target cuproproteins distributed in the various bacterial compartments. As a result, new questions have emerged regarding the diversity and apparent redundancies of these components, their irregular presence in different organisms, functional interactions, and resulting system architectures.

Investigating the role of zinc and copper binding motifs of trafficking sites in the cyanobacterium Synechocystis PCC 6803

Although zinc and copper are required by proteins with very different functions, these metals can be delivered to cellular locations by homologous metal transporters within the same organism, as demonstrated by the cyanobacterial ( Synechocystis PCC 6803) zinc exporter ZiaA and thylakoidal copper importer PacS. The N-terminal metal-binding domains of these transporters (ZiaAN and PacSN, respectively) have related ferredoxin folds also found in the metallochaperone Atx1, which delivers copper to PacS, but differ in the residues found in their M/IXCXXC metal-binding motifs. To investigate the role of the nonconserved residues in this region on metal binding, the sequence from ZiaAN has been introduced into Atx1 and PacSN, and the motifs of Atx1 and PacSN swapped. The motif sequence can tune Cu(I) affinity only approximately 3-fold. However, the introduction of the ZiaAN motif (MDCTSC) dramatically increases the Zn(II) affinity of both Atx1 and PacSN by up to 2 orders of magnitude. The Atx1 mutant with the ZiaAN motif crystallizes as a side-to-side homodimer very similar to that found for [Cu(I)2-Atx1]2 ( Badarau et al. Biochemistry 2010 , 49 , 7798 ). In a crystal structure of the PacSN mutant possessing the ZiaAN motif (PacSN(ZiaAN)), the Asp residue from the metal-binding motif coordinates Zn(II). This demonstrates that the increased Zn(II) affinity of this variant and the high Zn(II) affinity of ZiaAN are due to the ability of the carboxylate to ligate this metal ion. Comparison of the Zn(II) sites in PacSN(ZiaAN) structures provides additional insight into Zn(II) trafficking in cyanobacteria.

Crosstalk between Cu(I) and Zn(II) homeostasis via Atx1 and cognate domains

The copper metallochaperone Atx1 and the N-terminal metal-binding domain of a copper-transporting ATP-ase can form tight Zn(II)-mediated hetero-complexes in both cyanobacteria and humans. Copper and zinc homeostasis could be linked by metal binding to these CXXC-containing proteins.

Periplasmic response upon disruption of transmembrane Cu transport in Pseudomonas aeruginosa

Pseudomonas aeruginosa, an opportunistic pathogen, has two transmembrane Cu(+) transport ATPases, CopA1 and CopA2. Both proteins export cytoplasmic Cu(+) into the periplasm and mutation of either gene leads to attenuation of virulence. CopA1 is required for maintaining cytoplasmic copper levels, while CopA2 provides copper for cytochrome c oxidase assembly. We hypothesized that transported Cu(+) ions would be directed to their destination via specific periplasmic partners and disruption of transport should affect the periplasmic copper homeostasis. Supporting this, mutation of either ATPase gene led to large increments in periplasmic cuproprotein levels. Toward identifying the proteins participating in this cellular response the periplasmic metalloproteome was resolved in non-denaturing bidimensional gel electrophoresis, followed by X-ray fluorescence visualization and identification by mass-spectrometry. A single spot containing the electron shuttle protein azurin was responsible for the observed increments in cuproprotein contents. In agreement, lack of either Cu(+)-ATPase induced an increase in azu transcription. This is associated with an increase in the expression of anr and rpoS oxidative stress response regulators, rather than cueR, a copper sensing regulator. We propose that azurin overexpression and accumulation in the periplasm is part of the cellular response to cytoplasmic oxidative stress in P. aeruginosa.

Function and evolution of channels and transporters in photosynthetic membranes

Chloroplasts from land plants and algae originated from an endosymbiotic event, most likely involving an ancestral photoautotrophic prokaryote related to cyanobacteria. Both chloroplasts and cyanobacteria have thylakoid membranes, harboring pigment-protein complexes that perform the light-dependent reactions of oxygenic photosynthesis. The composition, function and regulation of these complexes have thus far been the major topics in thylakoid membrane research. For many decades, we have also accumulated biochemical and electrophysiological evidence for the existence of solute transthylakoid transport activities that affect photosynthesis. However, research dedicated to molecular identification of the responsible proteins has only recently emerged with the explosion of genomic information. Here we review the current knowledge about channels and transporters from the thylakoid membrane of Arabidopsis thaliana and of the cyanobacterium Synechocystis sp. PCC 6803. No homologues of these proteins have been characterized in algae, although similar sequences could be recognized in many of the available sequenced genomes. Based on phylogenetic analyses, we hypothesize a host origin for most of the so far identified Arabidopsis thylakoid channels and transporters. Additionally, the shift from a non-thylakoid to a thylakoid location appears to have occurred at different times for different transport proteins. We propose that closer control of and provision for the thylakoid by products of the host genome has been an ongoing process, rather than a one-step event. Some of the proteins recruited to serve in the thylakoid may have been the result of the increased specialization of its pigment-protein composition and organization in green plants.

Coproporphyrin III excretion identifies the anaerobic coproporphyrinogen III oxidase HemN as a copper target in the Cu⁺-ATPase mutant copA⁻ of Rubrivivax gelatinosus

Two genes encoding structurally similar Copper P1B -type ATPases can be identified in several genomes. Notwithstanding the high sequence and structural similarities these ATPases held, it has been suggested that they fulfil distinct physiological roles. In deed, we have shown that the Cu(+) -ATPase CtpA is required only for the activity of cuproproteins in the purple bacterium Rubrivivax gelatinosus; herein, we show that CopA is not directly required for cytochrome c oxidase but is vital for copper tolerance. Interestingly, excess copper in the copA(-) mutant resulted in a substantial decrease of the cytochrome c oxidase and the photosystem under microaerobic and anaerobic conditions together with the extrusion of coproporphyrin III. The data indicated that copper targeted the tetrapyrrole biosynthesis pathway at the level of the coproporphyrinogen III oxidase HemN and thereby affects the oxidase and the photosystem. This is the first in vivo demonstration that copper, like oxygen, affects tetrapyrrole biosynthesis presumably at the level of the SAM and [4Fe-4S] containing HemN enzyme. In light of these results and similar findings in Escherichia coli, the potential role of copper ions in the evolution of [4Fe-4S] enzymes and the Cu(+) -ATPases is discussed.

Mechanisms of metal resistance and homeostasis in haloarchaea

Haloarchaea are the predominant microflora of hypersaline econiches such as solar salterns, soda lakes, and estuaries where the salinity ranges from 35 to 400 ppt. Econiches like estuaries and solar crystallizer ponds may contain high concentrations of metals since they serve as ecological sinks for metal pollution and also as effective traps for river borne metals. The availability of metals in these econiches is determined by the type of metal complexes formed and the solubility of the metal species at such high salinity. Haloarchaea have developed specialized mechanisms for the uptake of metals required for various key physiological processes and are not readily available at high salinity, beside evolving resistance mechanisms for metals with high solubility. The present paper seeks to give an overview of the main molecular mechanisms involved in metal tolerance in haloarchaea and focuses on factors such as salinity and metal speciation that affect the bioavailability of metals to haloarchaea. Global transcriptomic analysis during metal stress in these organisms will help in determining the various factors differentially regulated and essential for metal physiology.

Redox control of copper homeostasis in cyanobacteria

Copper is essential for all living organisms but is toxic when present in excess. Therefore organisms have developed homeostatic mechanism to tightly regulate its cellular concentration. In a recent study we have shown that CopRS two-component system is essential for copper resistance in the cyanobacterium Synechocystis sp PCC 6803. This two-component regulates expression of a heavy-metal RND type copper efflux system (encoded by copBAC) as well as its own expression (in the copMRS operon) in response to an excess of copper in the media. We have also observed that both operons are induced under condition that reduces the photosynthetic electron flow and this induction depends on the presence of the copper-protein, plastocyanin. These findings, together with CopS localization to the thylakoid membrane and its periplasmic domain being able to bind copper directly, suggest that CopS could be involved in copper detection in both the periplasm and the thylakoid lumen.

Reconstruction and comparison of the metabolic potential of cyanobacteria Cyanothece sp. ATCC 51142 and Synechocystis sp. PCC 6803

Cyanobacteria are an important group of photoautotrophic organisms that can synthesize valuable bio-products by harnessing solar energy. They are endowed with high photosynthetic efficiencies and diverse metabolic capabilities that confer the ability to convert solar energy into a variety of biofuels and their precursors. However, less well studied are the similarities and differences in metabolism of different species of cyanobacteria as they pertain to their suitability as microbial production chassis. Here we assemble, update and compare genome-scale models (iCyt773 and iSyn731) for two phylogenetically related cyanobacterial species, namely Cyanothece sp. ATCC 51142 and Synechocystis sp. PCC 6803. All reactions are elementally and charge balanced and localized into four different intracellular compartments (i.e., periplasm, cytosol, carboxysome and thylakoid lumen) and biomass descriptions are derived based on experimental measurements. Newly added reactions absent in earlier models (266 and 322, respectively) span most metabolic pathways with an emphasis on lipid biosynthesis. All thermodynamically infeasible loops are identified and eliminated from both models. Comparisons of model predictions against gene essentiality data reveal a specificity of 0.94 (94/100) and a sensitivity of 1 (19/19) for the Synechocystis iSyn731 model. The diurnal rhythm of Cyanothece 51142 metabolism is modeled by constructing separate (light/dark) biomass equations and introducing regulatory restrictions over light and dark phases. Specific metabolic pathway differences between the two cyanobacteria alluding to different bio-production potentials are reflected in both models.

The CopRS two-component system is responsible for resistance to copper in the cyanobacterium Synechocystis sp. PCC 6803

Photosynthetic organisms need copper for cytochrome oxidase and for plastocyanin in the fundamental processes of respiration and photosynthesis. However, excess of free copper is detrimental inside the cells and therefore organisms have developed homeostatic mechanisms to tightly regulate its acquisition, sequestration, and efflux. Herein we show that the CopRS two-component system (also known as Hik31-Rre34) is essential for copper resistance in Synechocystis sp. PCC 6803. It regulates expression of a putative heavy-metal efflux-resistance nodulation and division type copper efflux system (encoded by copBAC) as well as its own expression (in the copMRS operon) in response to the presence of copper in the media. Mutants in this two-component system or the efflux system render cells more sensitive to the presence of copper in the media and accumulate more intracellular copper than the wild type. Furthermore, CopS periplasmic domain is able to bind copper, suggesting that CopS could be able to detect copper directly. Both operons (copMRS and copBAC) are also induced by the photosynthetic inhibitor 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone but this induction requires the presence of copper in the media. The reduced response of two mutant strains to copper, one lacking plastocyanin and a second one impaired in copper transport to the thylakoid, due to the absence of the P(I)-type ATPases PacS and CtaA, suggests that CopS can detect intracellular copper. In addition, a tagged version of CopS with a triple HA epitope localizes to both the plasma and the thylakoid membranes, suggesting that CopS could be involved in copper detection in both the periplasm and the thylakoid lumen.

The ATPases CopA and CopB both contribute to copper resistance of the thermoacidophilic archaeon Sulfolobus solfataricus

Certain heavy metal ions such as copper and zinc serve as essential cofactors of many enzymes, but are toxic at high concentrations. Thus, intracellular levels have to be subtly balanced. P-type ATPases of the P(IB)-subclass play a major role in metal homeostasis. The thermoacidophile Sulfolobus solfataricus possesses two P(IB)-ATPases named CopA and CopB. Both enzymes are present in cells grown in copper-depleted medium and are accumulated upon an increase in the external copper concentration. We studied the physiological roles of both ATPases by disrupting genes copA and copB. Neither of them affected the sensitivity of S. solfataricus to reactive oxygen species, nor were they a strict prerequisite to the biosynthesis of the copper protein cytochrome oxidase. Deletion mutant analysis demonstrated that CopA is an effective copper pump at low and high copper concentrations. CopB appeared to be a low-affinity copper export ATPase, which was only relevant if the media copper concentration was exceedingly high. CopA and CopB thus act as resistance factors to copper ions at overlapping concentrations. Moreover, growth tests on solid media indicated that both ATPases are involved in resistance to silver.

Cytosolic Ni(II) sensor in cyanobacterium: nickel detection follows nickel affinity across four families of metal sensors

Efflux of surplus Ni(II) across the outer and inner membranes of Synechocystis PCC 6803 is mediated by the Nrs system under the control of a sensor of periplasmic Ni(II), NrsS. Here, we show that the product of ORF sll0176, which encodes a CsoR/RcnR-like protein now designated InrS (for internal nickel-responsive sensor), represses nrsD (NrsD is deduced to efflux Ni(II) across the inner membrane) from a cryptic promoter between the final two ORFs in the nrs operon. Transcripts initiated from the newly identified nrsD promoter accumulate in response to nickel or cobalt but not copper, and recombinant InrS forms specific, Ni(II)-inhibited complexes with the nrsD promoter region. Metal-dependent difference spectra of Ni(II)- and Cu(I)-InrS are similar to Cu(I)-sensing CsoR and dissimilar to Ni(II)/Co(II)-sensing RcnR, consistent with factors beyond the primary coordination sphere switching metal selectivity. Competition with chelators mag-fura-2, nitrilotriacetic acid, EDTA, and EGTA estimate K_D Ni(II) for the tightest site of InrS as 2.05 (±1.5) × 10⁻¹⁴m, and weaker K_D Ni(II) for the cells' metal sensors of other types: Zn(II) co-repressor Zur, Co(II) activator CoaR, and Zn(II) derepressor ZiaR. Ni(II) transfer to InrS occurs upon addition to Ni(II) forms of each other sensor. InrS binds Ni(II) sufficiently tightly to derepress Ni(II) export at concentrations below K_D Ni(II) of the other sensors.

Novel transporter required for biogenesis of cbb3-type cytochrome c oxidase in Rhodobacter capsulatus

The acquisition, delivery, and incorporation of metals into their respective metalloproteins are important cellular processes. These processes are tightly controlled in order to prevent exposure of cells to free-metal concentrations that could yield oxidative damage. Copper (Cu) is one such metal that is required as a cofactor in a variety of proteins. However, when present in excessive amounts, Cu is toxic due to its oxidative capability. Cytochrome c oxidases (Coxs) are among the metalloproteins whose assembly and activity require the presence of Cu in their catalytic subunits. In this study, we focused on the acquisition of Cu for incorporation into the heme-Cu binuclear center of the cbb(3)-type Cox (cbb(3)-Cox) in the facultative phototroph Rhodobacter capsulatus. Genetic screens identified a cbb(3)-Cox defective mutant that requires Cu(2+) supplementation to produce an active cbb(3)-Cox. Complementation of this mutant using wild-type genomic libraries unveiled a novel gene (ccoA) required for cbb(3)-Cox biogenesis. In the absence of CcoA, the cellular Cu content decreases and cbb(3)-Cox assembly and activity become defective. CcoA shows homology to major facilitator superfamily (MFS)-type transporter proteins. Members of this family are known to transport small solutes or drugs, but so far, no MFS protein has been implicated in cbb(3)-Cox biogenesis. These findings provide novel insights into the maturation and assembly of membrane-integral metalloproteins and on a hitherto-unknown function(s) of MFS-type transporters in bacterial Cu acquisition.

IMPORTANCE

Biogenesis of energy-transducing membrane-integral enzymes, like the heme copper-containing cytochrome c oxidases, and the acquisition of transition metals, like copper, as their catalytic cofactors are vital processes for all cells. These widespread and well-controlled processes are poorly understood in all organisms, including bacteria. Defects in these processes lead to severe mitochondrial diseases in humans and poor crop yields in plants. In this study, using the facultative phototroph Rhodobacter capsulatus as a model organism, we report on the discovery of a novel major facilitator superfamily (MFS)-type transporter (CcoA) that affects cellular copper content and cbb(3)-type cytochrome c oxidase production in bacteria.

Toward a molecular understanding of metal transport by P(1B)-type ATPases

The P(1B) family of P-type ATPases couples the transport of cytoplasmic transition metals across biological membranes to the hydrolysis of ATP. These ubiquitous transporters function in maintaining cytoplasmic metal quotas and in the assembly of metalloproteins, and have been classified into subfamilies (P(1B-1)-P(1B-5)) on the basis of their transported substrates (Cu(+), Zn(2+), Cu(2+), and Co(2+)) and signature sequences in their transmembrane segments. In addition, each subgroup presents a characteristic membrane topology and specific regulatory cytoplasmic metal-binding domains. In recent years, significant major aspects of their transport mechanism have been described, including the stoichiometry of transport and the delivery of substrates to transport sites by metallochaperones. Toward understanding their structure, the metal coordination by transport sites has been characterized for Cu(+) and Zn(2+)-ATPases. In addition, atomic resolution structures have been determined, providing key insight into the elements that enable transition metal transport. Because the Cu(+)-transporting ATPases are found in humans and are linked to disease, this subfamily has been the focus of intense study. As a result, significant progress has been made toward understanding Cu(+)-ATPase function on the molecular level, using both the human proteins and the bacterial homologs, most notably the CopA proteins from Archaeoglobus fulgidus, Bacillus subtilis, and Thermotoga maritima. This chapter thus focuses on the mechanistic and structural information obtained by studying these latter Cu(+)-ATPases, with some consideration of how these aspects might differ for the other subfamilies of P(1B)-ATPases.

Cyanobacterial metallochaperone inhibits deleterious side reactions of copper

Copper metallochaperones supply copper to cupro-proteins through copper-mediated protein-protein-interactions and it has been hypothesized that metallochaperones thereby inhibit copper from causing damage en route. Evidence is presented in support of this latter role for cyanobacterial metallochaperone, Atx1. In cyanobacteria Atx1 contributes towards the supply of copper to plastocyanin inside thylakoids but it is shown here that in copper-replete medium, copper can reach plastocyanin without Atx1. Unlike metallochaperone-independent copper-supply to superoxide dismutase in eukaryotes, glutathione is not essential for Atx1-independent supply to plastocyanin: Double mutants missing atx1 and gshB (encoding glutathione synthetase) accumulate the same number of atoms of copper per cell in the plastocyanin pool as wild type. Critically, Δatx1ΔgshB are hypersensitive to elevated copper relative to wild type cells and also relative to ΔgshB single mutants with evidence that hypersensitivity arises due to the mislocation of copper to sites for other metals including iron and zinc. The zinc site on the amino-terminal domain (ZiaA(N)) of the P(1)-type zinc-transporting ATPase is especially similar to the copper site of the Atx1 target PacS(N), and ZiaA(N) will bind Cu(I) more tightly than zinc. An NMR model of a substituted-ZiaA(N)-Cu(I)-Atx1 heterodimer has been generated making it possible to visualize a juxtaposition of residues surrounding the ZiaA(N) zinc site, including Asp(18), which normally repulse Atx1. Equivalent repulsion between bacterial copper metallochaperones and the amino-terminal regions of P(1)-type ATPases for metals other than Cu(I) is conserved, again consistent with a role for copper metallochaperones to withhold copper from binding sites for other metals.