Complex IV (CIV) is a copper-heme oxidase that couples electron transfer from cytochrome c to oxygen with proton extrusion across the inner membrane to contribute to the proton gradient required for ATP generation. This entry includes fungal mitochondrial complex IV assembly factor Cox20 [1] and its homologues (also known as FAM36A in metazoa [2]. Human CIV is formed by three catalytic core subunits (COX1/2/3). COX20 has been found to form a complex with SCO1, SCO2, and newly synthesized COX2. It may act as a chaperone in the early steps of COX2 maturation [3].

1: Identification of Cox20p, a novel protein involved in the maturation and assembly of cytochrome oxidase subunit 2. Hell K, Tzagoloff A, Neupert W, Stuart RA; J Biol Chem. 2000;275:4571-4578. PMID:10671482

2: A mutation in the FAM36A gene, the human ortholog of COX20, impairs cytochrome c oxidase assembly and is associated with ataxia and muscle hypotonia. Szklarczyk R, Wanschers BF, Nijtmans LG, Rodenburg RJ, Zschocke J, Dikow N, van den Brand MA, Hendriks-Franssen MG, Gilissen C, Veltman JA, Nooteboom M, Koopman WJ, Willems PH, Smeitink JA, Huynen MA, van den Heuvel LP; Hum Mol Genet. 2013;22:656-667. PMID:23125284

3: Human COX20 cooperates with SCO1 and SCO2 to mature COX2 and promote the assembly of cytochrome c oxidase. Bourens M, Boulet A, Leary SC, Barrientos A; Hum Mol Genet. 2014;23:2901-2913. PMID:24403053