The fungal cytochrome c oxidase subunit VIIa, encoded by the gene COX9, is a subunit of the cytochrome c oxidase (CcO, also called complex IV or CIV), the terminal oxidase in the mitochondrial electron transport chain which drives oxidative phosphorylation. CcO is a multi-chain transmembrane protein complex located in the inner membrane of mitochondria and the cell membrane of prokaryotes. It catalyzes the reduction of O2 and simultaneously pumps protons across the membrane. The number of subunits varies from three to five in bacteria and up to 14 in mammalian mitochondria. Subunits I, II, and III of mammalian CcO are encoded within the mitochondrial genome and the remaining 11 subunits are encoded within the nuclear genome. The VIIa subunit is the fungal homolog to subunit VIc in higher eukaryotes. It is a single-pass membrane protein and its specific function remains unclear.
Jiyao W et al.(2023). "The conserved domain database in 2023.",