Involved in the maturation of the mitochondrial respiratory chain complex IV subunit MT-CO2/COX2. Thereby, may regulate early steps of complex IV assembly. Mitochondrial respiratory chain complex IV or cytochrome c oxidase is the component of the respiratory chain that catalyzes the transfer of electrons from intermembrane space cytochrome c to molecular oxygen in the matrix and as a consequence contributes to the proton gradient involved in mitochondrial ATP synthesis. May also be required for efficient formation of respiratory supercomplexes comprised of complexes III and IV. Interacts with COA1 (PubMed:22356826). Found in a complex with TMEM177, COX20, MT-CO2/COX2, COX18, SCO1 and SCO2 (PubMed:29154948). Interacts with MT-CO2/COX2 and SCO2 (PubMed:25959673). Interacts with SCO1 (PubMed:26160915). Interacts with COX20 in a MT-CO2/COX2- and COX18-dependent manner (PubMed:29154948, PubMed:28330871). Interacts with COX16 (PubMed:29381136). The disease is caused by variants affecting the gene represented in this entry. Belongs to the cytochrome c oxidase subunit 6B family. Extended N-terminus. Contaminating sequence. cytochrome c oxidase assembly factor 6 homolog (S. cerevisiae) (COA6)