A Copper Relay System Involving Two Periplasmic Chaperones Drives cbb₃-Type Cytochrome c Oxidase Biogenesis in Rhodobacter capsulatus

Abstract

PccA and SenC are periplasmic copper chaperones required for the biogenesis of cbb3-type cytochrome c oxidase (cbb3-Cox) in Rhodobacter capsulatus at physiological Cu concentrations. However, both proteins are dispensable for cbb3-Cox assembly when the external Cu concentration is high. PccA and SenC bind Cu using Met and His residues and Cys and His residues as ligands, respectively, and both proteins form a complex during cbb3-Cox biogenesis. SenC also interacts directly with cbb3-Cox, as shown by chemical cross-linking. Here we determined the periplasmic concentrations of both proteins in vivo and analyzed their Cu binding stoichiometries and their Cu(I) and Cu(II) binding affinity constants (KD) in vitro. Our data show that both proteins bind a single Cu atom with high affinity. In vitro Cu transfer assays demonstrate Cu transfer both from PccA to SenC and from SenC to PccA at similar levels. We conclude that PccA and SenC constitute a Cu relay system that facilitates Cu delivery to cbb3-Cox.

The Cu chaperone CopZ is required for Cu homeostasis in Rhodobacter capsulatus and influences cytochrome cbb3 oxidase assembly

“…An alternative explanation is that Cu is transferred from both CopA and CcoI to dedicated periplasmic Cu chaperones, as has been shown for E. coli CopA that transfers Cu directly to CusF (Padilla‐Benavides et al , ). In the case of R. capsulatus two periplasmic chaperones, PccA and SenC, link Cu export via CcoI to cbb 3 ‐Cox assembly (Lohmeyer et al , ; Trasnea et al , ; ), although which one is the direct acceptor remains to be determined. The constraints of CopA and CcoI to interact with only dedicated Cu chaperones in the periplasm could be important for maintaining homeostasis between cuproprotein assembly and controlling Cu toxicity.…”

“…Cytoplasmic Cu is exported back to the periplasm by the P 1B ‐type ATPase CcoI (Koch et al , ; Ekici et al , ). In the periplasm, Cu is transferred to cbb 3 ‐Cox via a periplasmic relay system involving the periplasmic Cu chaperones PccA (a PCuAC‐homologue) and SenC (a Sco1‐homologue) (Kulajta et al , ; Lohmeyer et al , ; Trasnea et al , ; ). Similar to the phenotype of the Δ ccoA strain, the very low cbb 3 ‐Cox activity of either senC ‐ or pccA ‐deletion strains can be rescued by increasing the Cu concentrations in the growth medium (Trasnea et al , ).…”

Genome wide transcriptomic analysis of the soil ammonia oxidizing archaeon Nitrososphaera viennensis upon exposure to copper limitation

“…This could also be true for N. viennensis as the cytochrome oxidase in Thaumarchaeota is classified as type aa 3 [46,47]. Whether or not Cu needs to be transported into the cell before incorporation (as for cbb 3 oxidase in the bacterium Rhodobacter capsulatus [48,49]) or whether this takes place in the (pseudo-)periplasm (as in the model for cytochrome aa 3 oxidase in Paracoccus denitrificans [50]) is unclear.…”

Biochemical pathway for the biosynthesis of the CuA center in bacterial cytochrome c oxidase

“…The B. diazofficiens pcuC gene was uncovered in a microarray-assisted screen for copper starvation-inducible genes by Serventi et al [41] who showed that a pcuC mutant had zero cytochrome c oxidase activity (aa 3 -type) and completely lacked the CoxA and CoxB subunits. Furthermore, the preference of PcuC for Cu 1+ was confirmed [34,41,42]. PcuC is now known to be present in a wide range of prokaryotes, primarily in Gram-negative aerobes (Table 1).…”