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Copper and iron are trace elements that form an indispensable part of many proteins and are crucial for the well-being of all cells. At the same time, the intracellular levels of these metals require careful regulation, as excess or deficiency may be lethal. P1B-ATPases are key players in metal homeostasis. They belong to the superfamily of P-type ATPases, transmembrane proteins present in virtually all life forms, are responsible for solute translocation across biological membranes. The goal of this thesis is to improve our understanding of the structural and functional roles of P1B-ATPases in metal homeostasis by focusing on the host-microbe interaction. The thesis first describes the importance of Cu+ distribution in the outcome of host-microbe interaction. Copper is an important element in host-microbe interactions, acting both as a catalyst in enzymes and as a potential toxin. Cu+-ATPases drive cytoplasmic Cu+ efflux and protect bacteria against metal overload. Many pathogenic and symbiotic bacteria contain multiple Cu+-ATPase genes within particular genetic environments, suggesting alternative roles for each resulting protein. This hypothesis was tested by characterizing five homologous Cu+-ATPases present in the symbiotic organism Sinorhizobium meliloti. Mutation of each gene led to different phenotypes and abnormal nodule development in the alfalfa host. Distinct responses were detected in free-living S. meliloti mutant strains exposed to metal and redox stresses. Differential gene expression was detected under Cu+, oxygen or nitrosative stress. These observations suggest that CopA1a maintains the cytoplasmic Cu+ quota and its expression is controlled by Cu+ levels. CopA1b is also regulated by Cu+ concentrations and is required during symbiosis for bacteroid maturation. CopA2-like proteins, FixI1 and FixI2, are necessary for the assembly of two different cytochrome c oxidases at different stages of bacterial life. CopA3 is a phylogenetically distinct Cu+-ATPase that does not contribute to Cu+ tolerance. It is regulated by redox stress and required during symbiosis. We postulated a model where non-redundant homologous Cu+-ATPases, operating under distinct regulation, transport Cu+ to different target proteins. In its second part, the thesis describes the novel Fe2+-ATPases and their influence in the host-microbe interaction. Little is known about iron efflux transporters in bacterial systems. Recently, the participation of Bacillus subtilis PfeT, a P1B4-ATPase, in cytoplasmic Fe2+ efflux has been proposed. We report here the distinct roles of mycobacterial P1B4-ATPases in the homeostasis of Co2+ and Fe2+. Mutation of Mycobacterium smegmatis ctpJ affects the homeostasis of both ions. Alternatively, a M. tuberculosis ctpJ mutant is more sensitive to Co2+ than Fe2+, while mutation of the homologous M. tuberculosis ctpD leads to Fe2+ sensitivity but no alterations in Co2+ homeostasis. In vitro, the three enzymes are activated by both Fe2+ and Co2+ and bind one equivalent of either ion at their transport site. However, equilibrium binding affinities and activity kinetics show that M. tuberculosis CtpD has higher affinity for Fe2+ and twice the Fe2+ stimulated activity than the CtpJs. These parameters are accompanied by a lower activation by and affinity for Co2+. Analysis of Fe2+ and Co2+ binding to CtpD by X-ray spectroscopy shows that both ions are coordinated by 5-6 O/N atoms with similar geometry. Mutagenesis studies suggest the involvement of invariant Ser, His and Glu in metal coordination. Interestingly, replacement of Cys in the conserved CPS sequence at the metal binding pocket leads to a large reduction in Fe2+ but not Co2+ binding affinity. We propose that CtpJ ATPases participate in the control of steady state Fe2+ levels. CtpD, required for M. tuberculosis virulence, is a high affinity Fe2+ transporter involved in the rapid response to iron dyshomeostasis generated upon redox stress. These studies provide significant insights into the metal selectivity, regulation, transport kinetics and functional diversity of homologous P1B-ATPases in Cu+ and Fe2+ homeostasis. Moreover, these biochemical characterizations can be integrated with the structural-functional analysis to elucidate the complex metal distribution networks.

SlyD is a protein involved in [NiFe]-hydrogenase enzyme maturation and, together with HypB and HypA proteins, contributes to the nickel delivery step. To understand the molecular details of this in vivo function, the nickel-binding activity of SlyD was investigated in vitro. SlyD is a monomeric protein that can chelate up to 7 nickel ions with an affinity in the sub-nanomolar range. By truncation and mutagenesis studies we show that the unique C-terminal metal-binding domain of this protein is required for Ni(II) binding and that the protein coordinates this metal non-cooperatively. This activity of SlyD supports the proposed in vivo role of SlyD in nickel homeostasis. In addition to nickel, SlyD can bind a variety of other types of transition metals. Therefore it was feasible that the protein contributes to homeostasis of metals other than nickel. To test this hypothesis, the metal selectivity of the protein was examined. The preference of SlyD for the metals examined could be ordered as follows, Mn(II), Fe(II) < Co(II) < Ni(II) ~ Zn(II) << Cu(I) indicating that the affinity of SlyD for the different metals follows the Irving-Williams series of metal-complex stabilities. Although the protein is unable to overcome the large thermodynamic preference in vitro for Cu(I) and exclude Zn(II) chelation, in vivo studies suggest a Ni(II)-specific function for the protein. To understand the function of SlyD as a metallochaperone, its interaction with HypB was investigated. This investigation revealed that SlyD plays a role in Ni(II) storage in E. coli and can function as a Ni(II)-donor to HypB. This study also revealed that SlyD can modulate the metal-binding as well as the GTPase activities of HypB. Based on the experimental data, a role for the HypB-SlyD complex in [NiFe]-hydrogenase biosynthesis is presented.

SlyD is a protein involved in [NiFe]-hydrogenase enzyme maturation and, together with HypB and HypA proteins, contributes to the nickel delivery step. To understand the molecular details of this in vivo function, the nickel-binding activity of SlyD was investigated in vitro. SlyD is a monomeric protein that can chelate up to 7 nickel ions with an affinity in the sub-nanomolar range. By truncation and mutagenesis studies we show that the unique C-terminal metal-binding domain of this protein is required for Ni(II) binding and that the protein coordinates this metal non-cooperatively. This activity of SlyD supports the proposed in vivo role of SlyD in nickel homeostasis. In addition to nickel, SlyD can bind a variety of other types of transition metals. Therefore it was feasible that the protein contributes to homeostasis of metals other than nickel. To test this hypothesis, the metal selectivity of the protein was examined. The preference of SlyD for the metals examined could be ordered as follows, Mn(II), Fe(II) < Co(II) < Ni(II) ~ Zn(II) << Cu(I) indicating that the affinity of SlyD for the different metals follows the Irving-Williams series of metal-complex stabilities. Although the protein is unable to overcome the large thermodynamic preference in vitro for Cu(I) and exclude Zn(II) chelation, in vivo studies suggest a Ni(II)-specific function for the protein. To understand the function of SlyD as a metallochaperone, its interaction with HypB was investigated. This investigation revealed that SlyD plays a role in Ni(II) storage in E. coli and can function as a Ni(II)-donor to HypB. This study also revealed that SlyD can modulate the metal-binding as well as the GTPase activities of HypB. Based on the experimental data, a role for the HypB-SlyD complex in [NiFe]-hydrogenase biosynthesis is presented.

Metal homeostasis in plants is regulated by diverse mechanisms that act together to maintain optimal metal ion concentrations inside the cell. P1B-ATPases are heavy metal transport ATPases that are likely to be related to these processes. The sequencing of the genome of Arabidopsis thaliana revealed the presence of eight putative P1B-ATPases, HMA1-8. The main goal in this work is to characterize of the role of P1B-ATPases in plant metal homeostasis. Toward this goal, the P1B-ATPases HMA1 and HMA6 from Arabidopsis thaliana were cloned from leaves and sequenced. Results from RT-PCR experiments show ubiquitous expression in planta of this two ATPases, except for HMA1 that does not express in roots. Upon Cu2+ exposure during growth, expression of HMA6 increases in seedlings. HMA1 expression increases when seedlings are grown in high Cu2+ and Co2+ media, and decreases when grown in high concentrations of Zn2+ and Ni2+. hma1-1 plants have smaller size and less chlorophyll content than WT plants. Growth is affected in hma1-1 seedlings when grown in Zn2+, Mn2+, Fe2+, Co2+ and Cu2+ deficient media, or when these metals are in excess. Moreover, hma1-1 plants show an increase in Zn2+, Mn2+ and Fe2+ content in whole plants compared to WT plants. Mutant plants also show increased levels of HMA3 and HMA4 transcripts (Zn2+/Cd2+/Pb2+ P1B-ATPases), upregulation of metallothioneins 1a and 2b, downregulation of metallothionein 1c, and a decrease in the phytochellatin synthases 1 and 2 transcripts, compared to WT plants. Homozygous for mutation in HMA6 seems to be lethal, given that none was recovered after screening. These results indicate HMA1 and HMA6 as essential components of plant metal homeostasis in Arabidopsis thaliana.

Group A Streptococcus (GAS) is a common pathogen of the human skin and mucosal surfaces and is capable of producing a variety of diseases. This dissertation investigates the function of a metalloregulator named MtsR in GAS physiology and disease process. An mtsR mutant was constructed and analyzed. Consistent with MtsR role in iron uptake regulation, the mtsR mutant accumulates more iron (80 ± 22.5%) than the wild type strain. Inactivation of mtsR results in constitutive transcription of the sia (Streptococcal Iron Acquisition) operon, which is negatively regulated by iron in the parent strain. We identified the promoter that controls the expression of the sia operon (Pshr) and used it as a model to study MtsR interaction with DNA. Electrophoretic mobility gel shift assays (EMSAs) demonstrated that MtsR binds to the shr upstream region specifically and in an iron and manganese dependent manner. DNase I footprint analysis revealed that MtsR protects a 69 bp segment in Pshr that includes 2 inverted repeats, overlapping the core promoter elements. A global transcriptional analysis determined that MtsR modulates the expression of 64 genes, of which 44 were upregulated and 20 were downregulated in the mtsR mutant. MtsR controls genes with diverse functions including immune evasion, colonization, dissemination, metal homeostasis, nucleic acid and amino acid metabolism, and protein stability. MtsR functions as a dual regulator as it binds to the promoters of the repressed genes ska, aroE, and nrdF.2, as well as the upstream region of the positively regulated genes mga, emm49, and pyrF. A 16 bp MtsR-binding consensus region was identified in all of the promoters that are directly regulated by MtsR. In conclusion, we have demonstrated that MtsR is a global regulator in GAS that controls the expression of vital virulence factors and genes involved in metal transport, virulence and metabolic pathways.

<p>Mechanisms of copper homeostasis are of great interest partly due to their connection to debilitating genetic and neurological disorders. The family of high-affinity copper transporters (Ctr) is responsible for extracellular copper acquisition and internalization in yeast, plants, and mammals, including human. The extracellular domain of the human high-affinity copper transporter (hCtr1) contains essential Cu-binding methionine-rich MXXM and MXM (Mets) motifs that are important for copper acquisition and transport. The hCtr1 extracellular domain also contains potential copper binding histidine (His) clusters, including a high-affinity Cu(II) ATCUN site. As of yet, extracellular His clusters have no established significance for hCtr1 function. We have made model peptides based on the extracellular copper acquisition domain of hCtr1 that is rich in His residues and Mets motifs. The peptides' Cu(I) and Cu(II) binding properties have been characterized by UV-Vis and mass spectrometry. Our findings have been extended to a mouse cell model and we show that His residues are important for hCtr1 function likely because of their contribution to strong copper-binding sites in the hCtr1 extracellular domain responsible for copper acquisition. </p> <p>Copper's pro-oxidant property is also medicinally promising if it can be harnessed to induce oxidative stress as a cancer chemotherapy strategy. Our lab has designed a photocleavable caged copper complex that can selectively release redox-active copper in response to light. The thermodynamic copper binding properties of these potential chemotherapeutics have been characterized</p> / Dissertation

The biosynthesis of [NiFe]-hydrogenase and urease in Helicobacter pylori requires several accessory proteins for proper assembly of the nickel-containing active sites. Critical to the maturation of both enzymes in H. pylori is the GTPase HypB. In this work, the metal-binding properties of H. pylori HypB (HpHypB) were investigated and a link between metal binding and the other biochemical properties of HpHypB was established. HpHypB binds stoichiometric nickel or zinc with nanomolar affinities, in partially overlapping sites located between two major GTPase motifs. Upon metal binding, the GTP hydrolysis activity and oligomeric properties of the protein are modulated. Furthermore, the stoichiometry and affinity of the nickel is altered when HpHypB is bound to nucleotide, a change not observed for zinc. Mutagenesis of the metal ligands suggest that a conserved cysteine is responsible for transducing the metal-bound state to altered GTPase activity and a conserved histidine is a required nickel ligand only in the nucleotide-bound state. Together, these results suggest that the metal-binding and GTP hydrolysis properties of HpHypB are intimately linked and may comprise a mechanism through which the [NiFe]-hydrogenase and urease maturation pathways can discriminate between Ni(II) and Zn(II). Characterization of the Escherichia coli GTPase YjiA, a member of the same GTPase family as HpHypB, demonstrated that YjiA can bind Ni(II), Zn(II), or Co(II) at a site in a similar location as in HpHypB. Metal binding also regulates the GTPase activity and oligomerization of YjiA. This finding suggests that metal-responsive GTPase activity may be a trait of this family of GTPases. Together, this work describes a unique link between the metal-binding and biochemical properties of the G3E GTPases and provides insight into the role of HpHypB in [NiFe]-hydrogenase and urease maturation.

The biosynthesis of [NiFe]-hydrogenase and urease in Helicobacter pylori requires several accessory proteins for proper assembly of the nickel-containing active sites. Critical to the maturation of both enzymes in H. pylori is the GTPase HypB. In this work, the metal-binding properties of H. pylori HypB (HpHypB) were investigated and a link between metal binding and the other biochemical properties of HpHypB was established. HpHypB binds stoichiometric nickel or zinc with nanomolar affinities, in partially overlapping sites located between two major GTPase motifs. Upon metal binding, the GTP hydrolysis activity and oligomeric properties of the protein are modulated. Furthermore, the stoichiometry and affinity of the nickel is altered when HpHypB is bound to nucleotide, a change not observed for zinc. Mutagenesis of the metal ligands suggest that a conserved cysteine is responsible for transducing the metal-bound state to altered GTPase activity and a conserved histidine is a required nickel ligand only in the nucleotide-bound state. Together, these results suggest that the metal-binding and GTP hydrolysis properties of HpHypB are intimately linked and may comprise a mechanism through which the [NiFe]-hydrogenase and urease maturation pathways can discriminate between Ni(II) and Zn(II). Characterization of the Escherichia coli GTPase YjiA, a member of the same GTPase family as HpHypB, demonstrated that YjiA can bind Ni(II), Zn(II), or Co(II) at a site in a similar location as in HpHypB. Metal binding also regulates the GTPase activity and oligomerization of YjiA. This finding suggests that metal-responsive GTPase activity may be a trait of this family of GTPases. Together, this work describes a unique link between the metal-binding and biochemical properties of the G3E GTPases and provides insight into the role of HpHypB in [NiFe]-hydrogenase and urease maturation.

La frataxine est une protéine mitochondriale bien conservée de la bactérie à l’homme. La déficience de la frataxine chez l’homme entraine une maladie neurodégénérative grave, appelée Ataxie de Friedreich. Cette protéine a été découverte dans les années 90s et depuis sa fonction physiologique exacte n’est toujours pas connue. La frataxine joue un rôle important dans la biosynthèse des centres Fe-S dans l’homéostasie du fer et/ou dans la protection contre le stress oxydant. Dans cette thèse, nous nous intéressons aux interactions entre la protéine et d’autres molécules, comme certains métaux mitochondriaux ou protéines pour mieux comprendre la fonction de la frataxine dans la cellule. Lors de ce travail, la frataxine de levure (Yfh1) a été synthétisée par la technique de l’ADN recombinant, puis purifiée pour les études physico-chimiques. La flavohémoglobine (Yhb1)qui joue le rôle important dans la détoxification de NO (un agent du stress oxydatif et nitrosatif) a été aussi exprimée et purifiée selon le même principe. Ensuite, nous avons étudié la thermodynamique et la cinétique de la complexation de Yfh1 par les métaux mitochondriaux comme Fe, Cu, Mn, Zn, ainsi qu’avec les protéines impliquées dans le système antioxydant comme les superoxydes dismutases, CuZnSOD et MnSOD, et la flavohémoglobine. Ces résultats montrent tout d’abord que Yfh1 interagit avec tous les métaux mitochondriaux,néanmoins elle présente une meilleure affinité pour le cuivre et le manganèse. Par la suite, nous mettons en évidence le rôle remarquable de la frataxine dans le système antioxydant. Nous attribuons ainsi à la frataxine un rôle de protéine multifonctionnelle : « régulateur » dans le métabolisme des métaux. / The frataxin is a mitochondrial protein which is highly conserved during the evolution. The deficiency of frataxinin human induces a neurodegenerative disease: Friedreich’s ataxia. This protein was discovered in the nineties.However, its functions are always opened questions. It has been shown that frataxin participates in the assemblyof Fe-S cluster, as well as the iron homeostasis and cellular antioxidant system. The interactions between frataxinand others molecules, such as metals or proteins, are necessary for a better understanding of protein’s functions.In this work, we synthesized a yeast frataxin homologue (Yfh1) by DNA recombinant technique, and thenpurified it for cell free studies. Yeast flavohemoglobin (Yhb1), which is responsible for the detoxification of NO(an oxidative and nitrosative stress agent), was also isolated. We started by determining the thermodynamics andkinetics of the physiological interaction between Yfh1 and mitochondrial metals, such as Fe, Cu, Mn and Zn, aswell as the interaction with the gatekeepers in the anti-oxidative stress such as superoxide dismutases, CuZnSOD& MnSOD, and Yhb1. We underline here, in the first part the unspecific interaction of Yfh1 with mitochondrialmetals, and more especially the higher affinity of Yfh1 for copper and manganese than for iron. We also confirmthe remarkable participation of Yfh1 in the antioxidant system. Based on these observations, we assume thatfrataxin plays the role of a “regulator” in metal metabolism.