Copper metallochaperone essential for the synthesis and maturation of cytochrome c oxidase subunit II (MT-CO2/COX2). Involved in transporting copper to the Cu(A) site on MT-CO2/COX2. Also acts as a thiol-disulfide oxidoreductase to regulate the redox state of the cysteines in SCO1 during maturation of MT-CO2/COX2. Homodimer. Interacts with COA6. Found in a complex with TMEM177, COX20, COA6, MT-CO2/COX2, COX18 and SCO1. Interacts with TMEM177 in a COX20-dependent manner. Interacts with COX20 in a MT-CO2/COX2- and COX18-dependent manner. Interacts with COX16. Belongs to the SCO1/2 family.