Involved in the assembly of cytochrome c oxidase. Imported into the mitochondria via the mitochondrial MIA40-ERV1 machinery. The twin Cx9C motifs are involved in the recognition by the mitochondrial MIA40-ERV1 disulfide relay system and the subsequent transfer of disulfide bonds by dithiol/disulfide exchange reactions to the newly imported protein. Belongs to the PET191 family.