Roles of the ccoGHIS gene products in the biogenesis of the cbb3-type cytochrome c oxidase

Abstract

In many bacteria the ccoGHIS cluster, located immediately downstream of the structural genes (ccoNOQP) of cytochrome cbb3 oxidase, is required for the biogenesis of this enzyme. Genetic analysis of ccoGHIS in Rhodobacter capsulatus demonstrated that ccoG, ccoH, ccoI and ccoS are expressed independently of each other, and do not form a simple operon. Absence of CcoG, which has putative (4Fe-4S) cluster binding motifs, does not significantly affect cytochrome cbb3 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 acquisition of copper for cytochrome cbb3 oxidase, since a CcoI-minus phenotype could be mimicked by copper ion starvation of a wild-type strain. Remarkably, the small protein CcoS, with a putative single transmembrane span, is essential for the incorporation of the redox-active prosthetic groups (heme b, heme b3 and Cu) into the cytochrome cbb3 oxidase. Thus, the ccoGHIS products are involved in several steps during the maturation of the cytochrome cbb3 oxidase. (C) 2000 Academic Press.