The ScoI homologue SenC is a copper binding protein that interacts directly with the cbb3-type cytochrome oxidase in Rhodobacter capsulatus

Sco proteins are widespread assembly factors for the Cu-A centre of aa(3)-type cytochrome oxidases in eukaryotic and prokaryotic organisms. However, Sco homologues are also found in bacteria like Rhodobacter capsulatus which lack aa3-type cytochrome oxidases and instead use a cbb(3)-type cytochrome oxidase (cbb(3) Cox) without a CuA centre as a terminal oxidase. In the current study, we have analyzed the role of Sco (SenC) during cbb(3) Cox assembly in R. capsulatus. In agreement with earlier works, we found a strong cbb(3) Cox defect in the absence of SenC that impairs the steady-state stability of the CcoN, CcoO and CcoP core subunits, without the accumulation of detectable assembly intermediates. In vivo cross-linking results demonstrate that SenC is in close proximity to the CcoP and CcoH subunits of cbb(3) Cox, suggesting that SenC interacts directly with cbb(3) Cox during its assembly. SenC binds copper and the cbb(3) Cox assembly defect in the absence of SenC can be rescued by the addition of least 0.5 mu M Cu. Neither copper nor SenC influenced the transcription of the ccoNOQP operon encoding for cbb(3) Cox. Transcription of senC itself was also not influenced by Cu unless the putative Cu-export ATPase Ccol was absent. As Ccol is specifically required for the cbb(3) Cox assembly, these data provide a direct link between Cu delivery to cbb(3) Cox and SenC function. (c) 2012 Elsevier B.V. All rights reserved.