The SCO (an acronym for Synthesis of Cytochrome c Oxidase) family is involved in biogenesis of respiratory and photosynthetic systems. Members of this family are required for the proper assembly of cytochrome c oxidase (COX). They contain a metal binding motif, typically CXXXC, which is located in a flexible loop. In yeast the SCO1 protein is specifically required for a post-translational step in the accumulation of subunits 1 and 2 of cytochrome c oxidase (COXI and COX-II) []. It is a mitochondrion-associated cytochrome c oxidase assembly factor, and a membrane-anchored protein possessing a soluble domain with a TRX fold []. The SCOP homologue in Bacillus subtilis is also required for the expression of cytochrome c oxidase []. It has been proposed that Sco1 specifically delivers copper to the CuA site, a dinuclear copper centre, of the COX II subunit. More recently, it has been argued that the redox sensitivity of the copper binding properties of Sco1 implies that it participates in signaling events rather than functioning as a chaperone that transfers copper to COX II [, ].The purple nonsulphur photosynthetic eubacterium Rhodobacter capsulatus is a versatile organism that can obtain cellular energy by several means, including the capture of light energy for photosynthesis as well as the use of light-independent respiration, in which molecular oxygen serves as a terminal electron acceptor. The SenC protein is required for optimal cytochrome c oxidase activity in aerobically grown R. capsulatus cells and is involved in the induction of structural polypeptides of the light-harvesting and reaction centre complexes [].Mutations in human Sco1 and Sco2 cause fatal infantile hepatoencephalomyopathy and cardioencephalomyopathy, respectively. Both disorders are associated with severe COX deficiency in affected tissues [].
