Roles of the ccoGHIS gene products in the biogenesis of the cbb(3)-type cytochrome c oxidase

In many bacteria the ccoGHIS cluster, located immediately downstream of the structural genes (ccoNOQP) of cytochrome cbb(3) oxidase, is required for t he biogenesis of this enzyme. Genetic analysis of ccoGHIS in Rhodobacter Ca psulatus demonstrated that ccoG, ccoH, ccoI and ccoS are expressed independ ently of each other, and do not form a simple operon. Absence of CcoG, whic h has putative (4Fe-4S) cluster binding motifs, does not significantly affe ct cytochrome cbb(3) oxidase activity. However, CcoH and CcoI are required for normal steady-state amounts of the enzyme. CcoI is highly homologous to ATP-dependent metal ion transporters, and appears to be involved in the ac quisition of copper for cytochrome cbb(3) oxidase, since a CcoI-minus pheno type could be mimicked by copper ion starvation of a wild-type strain. Rema rkably, the small protein CcoS, with a putative single transmembrane span, is essential for the incorporation of the redox-active prosthetic groups (h eme b, heme b(3) and Cu) into the cytochrome cbb(3) oxidase. Thus, the ccoC HIS products are involved in several steps during the maturation of the cyt ochrome cbb(3) oxidase. (C) 2000 Academic Press.