COX17 is a copper metallochaperone involved in the assembly of cytochrome c oxidase (respiratory chain complex IV, CIV). It binds two copper ions and delivers them to the metallochaperones SCO1 and SCO2. These co-chaperone the copper to the Cu(A) site on cytochrome c oxidase subunit II (MT-CO2/COX2). COX17 also passes copper to the metallochaperone COX11, which relays it to the Cu(B) site on cytochrome c oxidase subunit I (MT-CO1/COX1).

Cytochrome c oxidase is the terminal component of the mitochondrial respiratory chain and catalyses electron transfer from reduced cytochrome c to oxygen. The complex is heteromeric, with three catalytic subunits encoded by mitochondrial genes and multiple structural subunits encoded by nuclear genes. The COX17 gene is nuclear, but its protein is not a structural subunit. It is thought to be involved in recruiting copper to mitochondria for incorporation into the COX apoenzyme. UniProt places it in the mitochondrial intermembrane space and the cytoplasm, and assigns it to the COX17 family.

HGNC classifies COX17 among the mitochondrial respiratory chain complex assembly factors. Earlier names refer to it as the yeast COX17 homologue, reflecting its origin in S. cerevisiae studies. The human protein shares 92% amino acid sequence identity with mouse and rat Cox17. The gene is no longer considered a candidate gene for COX deficiency, and a pseudogene, COX17P, lies on chromosome 13.