SURF1 superfamily. Surf1/Shy1 has been implicated in the posttranslational steps of the biogenesis of the mitochondrially-encoded Cox1 subunit of cytochrome c oxidase (complex IV). Cytochrome c oxidase (complex IV), the terminal electron-transferring complex of the respiratory chain, is an assemblage of nuclear and mitochondrially-encoded subunits. Its assembly is mediated by nuclear encoded assembly factors, one of which is Surf1/Shy1. Mutations in human Surf1 are a major cause of Leigh syndrome, a severe neurodegenerative disorder.