The roles of Rhodobacter sphaeroides copper chaperones PCuAC and Sco (PrrC) in the assembly of the copper centers of the aa3-type and the cbb3-type cytochrome c oxidases

The alpha proteobacter Rhodobacter sphaeroides accumulates two cytochrome c oxidases (CcO) in its cytoplasmic membrane during aerobic growth: a mitochondrial-like aa(3)-type CcO containing a di-copper Cu-A center and mono-copper Cu-B, plus a cbb(3)-type CcO that contains Cu-B but lacks Cu-A. Three copper chaperones are located in the periplasm of R. sphaeroides, PCuAC, PrrC (Sco) and Cox11. Cox11 is required to assemble Cu-B of the aa(3)-type but not the cbb(3)-type CcO. PrrC is homologous to mitochondrial Sco1; Sco proteins are implicated in Cu-A assembly in mitochondria and bacteria, and with Cu-B assembly of the cbb(3)-type CcO. PCuAC is present in many bacteria, but not mitochondria. PCuAC of Therm us thermophilus metallates a Cu-A center in vitro, but its in vivo function has not been explored. Here, the extent of copper center assembly in the aa(3)- and cbb(3)-type CcOs of R. sphaeroides has been examined in strains lacking PCuAC, PrrC, or both. The absence of either chaperone strongly lowers the accumulation of both CcOs in the cells grown in low concentrations of Cu2+. The absence of PrrC has a greater effect than the absence of PCuAC and PCuAC appears to function upstream of PrrC. Analysis of purified aa(3)-type CcO shows that PrrC has a greater effect on the assembly of its Cu-A than does PCuAC, and both chaperones have a lesser but significant effect on the assembly of its Cu-B even though Cox11 is present. Scenarios for the cellular roles of PCuAC and PrrC are considered. The results are most consistent with a role for PrrC in the capture and delivery of copper to Cu-A of the aa(3)-type CcO and to Cu-B of the cbb(3)-type CcO, while the predominant role of PCuAC may be to capture and deliver copper to PrrC and Cox11. This article is part of a Special Issue entitled: Biogenesis/Assembly of Respiratory Enzyme Complexes. (C) 2012 Elsevier B.V. All rights reserved.