Ytka (Ctak) And Yozb (Ctam) Function In The Biogenesis Of Cytochrome C Oxidase In Bacillus Subtilis

Cytochrome c oxidase in the respiratory chain of bacteria and mitochondria couples the reduction of molecular oxygen to form water with the generation of a transmembrane proton gradient. Bacillus subtilis has two heme A-containing heme-copper oxidases: the menaquinol oxidase cytochrome aa(3) and the cytochrome c oxidase cytochrome caa(3). By screening three collections of mutants for defective cytochrome c oxidase, we found the genes for two, new membrane-bound assembly factors in B. subtilis: ytkA and yozB (renamed ctaK and ctaM, respectively). CtaK is a lipoprotein without sequence similarity to any protein of known function. We show that CtaK functions together with Sco1 (YpmQ) in a pathway, leading to the assembly of the Cu-A center in cytochrome caa(3) and seems to be a functional analogue to proteins of the periplasmic Cu-A chaperone family (PCuAC). CtaM is required for the activity of both cytochrome caa(3) and cytochrome aa(3) and dispensable for the insertion of heme A into these oxidases. The orthologous Bacillus anthracis protein and the distantly related Staphylococcus aureus CtaM complemented CtaM deficiency in B. subtilis, establishing a common function of CtaM in these bacteria. As the overall result of our work, 12 different proteins are known to function in the biosynthesis of cytochrome c oxidase in B. subtilis.