Metal reservoirs & intracellular fluxes : characterization of three chaperone proteins contributing to zinc homeostasis in Cupriavidus metallidurans
Final Report Abstract
Zinc is a borderline metal that does not change its redox state under physiological conditions. The divalent zinc ions are essential for all forms of life, even those that do not need iron. This project investigated zinc homeostasis in the metal-resistant model organism Cupriavidus metallidurans strain CH34, which belongs to the bea-proteobacteria. The bacterium is able to maintain its zinc homeostasis from nM to mM Zn(II) concentrations in the growth medium, and in the presence of large concentrations of other metal cations that might compete with zinc. Central to this ability is a flow equilibrium of metal uptake and efflux processes, which maintains the steady state of the cytoplasmic concentrations of zinc and other metals. Although formally a futile cycle, the transport processes adjust the cytoplasmic concentrations of individual metal cations and the composition of the overall metal bouquet. While metal import can be mediated by various uptake systems with broad substrate specificity, metal efflux systems were assigned to one or two target ions. Metal-binding components of the cytoplasm interacted with these transport processes and two metal-binding GTPases (CobW2, CobW3) were directors of all these processes. While pulse-chase experiments studied the interaction of C. metallidurans with Zn(II) in the range of up to 40 min, transcriptomic and proteomic measurements determined those in the first minutes and few hours, respectively. At very low zinc concentrations, Zn(II) could be partially substituted by cobalt ions. Co(II) may for instance metalate a GTP cyclohydrolase that initiates folate biosynthesis. The zinc importer ZupT, the two GTPases and the Co(II) efflux system DmeF mediate this cross-road of Co(II) and Zn(II) homeostasis. The respective genes are under control of the zinc uptake regulator Zur of the Fur family. With increasing zinc availability, Co(II) is no longer used as Zn(II) substitute. The efflux system ZntA interacts with the zinc importers to form the flow equilibrium. ZntA is under control of the MerR-type regulator ZntR and also a cadmium efflux system. When the Cd(II) concentration becomes too high to allow efficient export by ZntA, the efflux system CadR supports ZntA. When, on the other hand, the Zn(II) concentration becomes too high, the efflux system CdfX helps ZntA. Survival at even higher zinc concentration is allowed by the transenvelope efflux complex CzcCBA, which exports Zn(II), Cd(II) and Co(II) from the periplasm to the outside. Action of CzcCBA is supported by additional efflux systems of the inner membrane, CzcD and CzcP, and periplasmic components. Overall, our studies provide a deep insight into multiple metal homeostasis in a metalresistant bacterium under a variety of metal concentrations. This knowledge can be used to understand similar processes in other bacteria with a much simpler outfit of genes involved in metal homeostasis, including pathogenic species.
Publications
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Behind the Shield of Czc: ZntR Controls Expression of the Gene for the Zinc-Exporting P-Type ATPase ZntA inCupriavidus metallidurans. Journal of Bacteriology, 203(11).
Schulz, Vladislava; Schmidt-Vogler, Christopher; Strohmeyer, Phillip; Weber, Stefanie; Kleemann, Daniel; Nies, Dietrich H. & Herzberg, Martin
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Chemical Constraints for Transition Metal Cation Allocation. Advances in Environmental Microbiology, 21-52. Springer International Publishing.
Nies, Dietrich H.
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How is a Zinc Ion Correctly Allocated to a Zinc-dependent Protein?. Advances in Environmental Microbiology, 579-660. Springer International Publishing.
Nies, Dietrich H.
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Importance of RpoD- and Non-RpoD-Dependent Expression of Horizontally Acquired Genes in Cupriavidus metallidurans. Microbiology Spectrum, 10(2).
Große, Cornelia; Grau, Jan; Große, Ivo & Nies, Dietrich H.
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Loss of Mobile Genomic Islands in Metal-Resistant, Hydrogen-Oxidizing Cupriavidus metallidurans. Applied and Environmental Microbiology, 88(4).
Große, Cornelia; Kohl, Thomas A.; Niemann, Stefan; Herzberg, Martin & Nies, Dietrich H.
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Interplay between Two-Component Regulatory Systems Is Involved in Control of Cupriavidus metallidurans Metal Resistance Genes. Journal of Bacteriology, 205(4).
Große, Cornelia; Scherer, Judith; Schleuder, Grit & Nies, Dietrich H.
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A flow equilibrium of zinc in cells of Cupriavidus metallidurans. Journal of Bacteriology, 206(5).
Nies, Dietrich H.; Schleuder, Grit; Galea, Diana & Herzberg, Martin
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Antisense transcription is associated with expression of metal resistance determinants in Cupriavidus metallidurans CH34. Metallomics, 16(12).
Große, Cornelia; Grau, Jan; Herzberg, Martin & Nies, Dietrich H.
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Linking the transcriptome to physiology: response of the proteome of Cupriavidus metallidurans to changing metal availability. Metallomics, 16(12).
Galea, Diana; Herzberg, Martin; Dobritzsch, Dirk; Fuszard, Matt & Nies, Dietrich H.
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Protecting the Achilles heel: three FolE_I-type GTP-cyclohydrolases needed for full growth of metal-resistant Cupriavidus metallidurans under a variety of conditions. Journal of Bacteriology, 206(2).
Schulz, Vladislava; Galea, Diana; Herzberg, Martin & Nies, Dietrich H.
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The efflux system CdfX exports zinc that cannot be transported by ZntA in Cupriavidus metallidurans. Journal of Bacteriology, 206(11).
Schulz, Vladislava; Galea, Diana; Schleuder, Grit; Strohmeyer, Philipp; Große, Cornelia; Herzberg, Martin & Nies, Dietrich H.
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The metal-binding GTPases CobW2 and CobW3 are at the crossroads of zinc and cobalt homeostasis in Cupriavidus metallidurans. Journal of Bacteriology, 206(8).
Galea, Diana; Herzberg, Martin & Nies, Dietrich H.
