The cbb3-type cytochrome c oxidase from Rhodobacter sphaeroides, a proton-pumping heme-copper oxidase

Rhodobacter sphaeroides expresses a bb3-type quinol oxidase, and two cytochrome c oxidases: cytochrome aa3 and cytochrome cbb3. We report here the characterization of the genes encoding this latter oxidase. The ccoNOQP gene cluster of R. sphaeroides contains four open reading frames with high similarity to all ccoNOQP/fixNOQP gene clusters reported so far. CcoN has the six highly conserved histidines proposed to be involved in binding the low spin heme, and the binuclear center metals. ccoO and ccoP code for membrane bound mono- and diheme cytochromes c. ccoQ codes for a small hydrophobic protein of unknown function. Upstream from the cluster there is a conserved Fnr/FixK-like box which may regulate its expression. Analysis of a R. sphaeroides mutant in which the ccoNOQP gene cluster was inactivated confirms that this cluster encodes the cbb3-type oxidase previously purified. Analysis of proton translocation in several strains shows that cytochrome cbb3 is a proton pump. We also conclude that cytochromes cbb3 and aa3 are the only cytochrome c oxidases in the respiratory chain of R. sphaeroides.