The zinc repository of Cupriavidus metallidurans

Abstract

Zinc is a central player in the metalloproteomes of prokaryotes and eukaryotes. We used a bottom-up quantitative proteomic approach to reveal the repository of the zinc pools in the proteobacterium Cupriavidus metallidurans. About 60% of the theoretical proteome of C. metallidurans was identified, quantified, and the defect in zinc allocation was compared between a ΔzupT mutant and its parent strain. In both strains, the number of zinc-binding proteins and their binding sites exceeded that of the zinc ions per cell, indicating that the totality of the zinc proteome provides empty binding sites for the incoming zinc ions. This zinc repository plays a central role in zinc homeostasis in C. metallidurans and probably also in other organisms.

The biological chemistry of the transition metal “transportome” of Cupriavidus metallidurans

“…7 are indicated. The numbers of proteins in the cell of the plasmid-free C. metallidurans strain AE104 and its ∆zupT mutant are from 9 . The numbers in green indicate up-regulation in AE104 compared to CH34, or in ∆zupT compared to AE104, number is red down-regulation.…”

“…metallidurans possesses the genes for 18 TonB-dependent outer membrane proteins, six of them were found in the proteome 9 . Three of these six proteins were again down-regulated in the ∆zupT mutant of strain AE104 (Table 5) but up-regulated in strain AE104 under conditions of metal starvation 14 : Rmet_0837, Rmet_1118, and Rmet_5373 encoding Fiu-, YncD-and FepA-like proteins, respectively.…”

“…Via this mechanism, and to prevent import into the cytoplasm, Cu(I) is: (i) oxidized by CopA/CueO/PcoA to the less toxic Cu(II); (ii) exported by CusCBA systems; (iii) sequestered by CusF and related proteins or accepted by these proteins from copper-exporters and passed on to CusCBA systems; (iv) sequestered/accepted by other periplasmic copper chaperones for delivery as cofactor to client proteins. Interestingly, synthesis of the Cu-Zn SodC in C. metallidurans also requires prior import of the zinc into the cytoplasm to deliver this ion efficiently to this periplasmic protein 9,94 . C. metallidurans contains a variety of possible metal-binding chaperones as part of the Czc system, e.g.…”

“…This indicates that CzcP is only able to reach some cytoplasmic zinc speciations or zinc pools while the P IB2 -type ATPases such as ZntA are able to reach all zinc species for removal and consequently detoxification. Since it is important for efficient zinc supply to zincdependent proteins if the ion was imported by ZupT or other importers, this indicates the presence of at least two, or perhaps three, zinc pools or speciations in the cytoplasm: loosely bound zinc ions that are imported by the other transport systems and can be removed by CzcP, and more tightly bound zinc imported by ZupT, which may need ZntA for export from the cytoplasm 9,94,129 .…”

“…Its genome contains 6717 protein-encoding genes located on a main chromosome, a second chromosome or "chromid", and two large plasmids named pMOL28 and pMOL30 to honor the laboratory in Belgium that isolated this strain 3 . More than half of the predicted proteins were quantified and identified in a bottom-up proteomic approach 9 .…”