Biogenesis of cbb3-type cytochrome c oxidase in Rhodobacter capsulatus

The cbb3-type cytochrome c oxidases (cbb3-Cox) constitute the second most abundant cytochrome c oxidase (Cox) group after the mitochondrial-like aa3-type Cox. They are present in bacteria only, and are considered to represent a primordial innovation in the domain of Eubacteria due to their phylogenetic distribution and their similarity to nitric oxide (NO) reductases. They are crucial for the onset of many anaerobic biological processes, such as anoxygenic photosynthesis or nitrogen fixation. In addition, they are prevalent in many pathogenic bacteria, and important for colonizing low oxygen tissues. Studies related to cbb3-Cox provide a fascinating paradigm for the biogenesis of sophisticated oligomeric membrane proteins. Complex subunit maturation and assembly machineries, producing the c-type cytochromes and the binuclear heme b3-CuB center, have to be coordinated precisely both temporally and spatially to yield a functional cbb3-Cox enzyme. In this review we summarize our current knowledge on the structure, regulation and assembly of cbb3-Cox, and provide a highly tentative model for cbb3-Cox assembly and formation of its heme b3-CuB binuclear center. This article is part of a Special Issue entitled: Biogenesis/Assembly of Respiratory Enzyme Complexes. ► Structure-function, regulation and biogenesis of cbb3-type Cox are reviewed. ► A multistep assembly pathway of the subunits of this membrane enzyme is discussed. ► A model for formation of the heme b3-CuB center of this enzyme is proposed.