CuA is a dinuclear copper site within the soluble domain of subunit II (Cox2) of bacterial and eukaryotic cytochrome c oxidases (CcOs), whose function is to convey electrons from a soluble cytochrome c to the catalytic heme a3-CuB centre of CcO. The proper assembly of the CuA site is essential for the catalytic machinery of a functional oxidase. In prokaryotes two protein families have been proposed to be involved in CuA site formation, with a key role in the delivery of metal ions to the CuA site. The first includes proteins that are able to bind Cu(I) through methionine and histidine residues arranged in a highly conserved H(M)X(10)MX(21)HXM motif 5 (referred to as periplasmic CuA chaperone, PCu(A)C). The second consists of the Sco proteins, whose mechanism of action in CuA assembly as thioredoxins or metallochaperones is still debated. These proteins (PCuAC and Sco) are often found in the same bacterial operon, and most of the identified operons that encode Sco also contain a gene for Cox2. PMID:18758441

This superfamily represents PCu(A)C, a periplasmic copper chaperone. It selectively inserts Cu(I) ions into subunit II of Thermus thermophilus ba3 oxidase to generate a native Cu(A) site. Its role may be to capture and transfer copper to two other copper chaperones, PrrC and Cox11, which in turn deliver Cu(I) to cytochrome c oxidase PMID:22248670.

INTERPRO:IPR007410, PFAM:PF04314,DOI:10.1038/nchembio.110