CtaG is required for formation of active cytochrome c oxidase in Bacillus subtilis

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Abstract
The Gram-positive bacteriumBacillus subtiliscontains two respiratory oxidases of the haem-copper superfamily: cytochromeaa3, which is a quinol oxidase, and cytochromecaa3, which is a cytochromecoxidase. Cytochromecoxidase uniquely contains a di-copper centre, CuA.B. subtilisCtaG is a membrane protein encoded by the same gene cluster as that which encodes the subunits of cytochromecoxidase. The role ofB. subtilisCtaG and orthologous proteins present in many other Gram-positive bacteria has remained unexplored. The sequence of CtaG is unrelated to that of CtaG/Cox11p of proteobacteria and eukaryotic cells. This study shows thatB. subtilisCtaG is essential for the formation of active cytochromecaa3but is not required for assembly of the core subunits I and II with haem in the membrane and it has no role in the synthesis of active cytochromeaa3.B. subtilisYpmQ, a homologue to Sco1p of eukaryotic cells, is also a membrane-bound cytochromecoxidase-specific assembly factor. Properties of CtaG- and YpmQ-deficient mutants were compared. Cells lacking YpmQ showed a low cytochromecoxidase activity and this defect was suppressed by the supplementation of the growth medium with copper ions. It has previously been proposed that YpmQ/Sco1p is involved in synthesis of the CuAcentre. The results of this study are consistent with this proposal but the exact role of YpmQ in assembly of cytochromecoxidase remains to be elucidated.