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

¹ Department of Cell and Organism Biology, Lund University, Sölvegatan 35, SE-22362 Lund, Sweden
² Department of Biological Chemistry, University of Copenhagen, Solvgade 83, DK-1307 Copenhagen K, Denmark

Correspondence
Lars Hederstedt
Lars.Hederstedt{at}cob.lu.se

The Gram-positive bacterium Bacillus subtilis contains two respiratory oxidases of the haem-copper superfamily: cytochrome aa₃, which is a quinol oxidase, and cytochrome caa₃, which is a cytochrome c oxidase. Cytochrome c oxidase uniquely contains a di-copper centre, Cu_A. B. subtilis CtaG is a membrane protein encoded by the same gene cluster as that which encodes the subunits of cytochrome c oxidase. The role of B. subtilis CtaG 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 that B. subtilis CtaG is essential for the formation of active cytochrome caa₃ but 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 cytochrome aa₃. B. subtilis YpmQ, a homologue to Sco1p of eukaryotic cells, is also a membrane-bound cytochrome c oxidase-specific assembly factor. Properties of CtaG- and YpmQ-deficient mutants were compared. Cells lacking YpmQ showed a low cytochrome c oxidase 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 Cu_A centre. The results of this study are consistent with this proposal but the exact role of YpmQ in assembly of cytochrome c oxidase remains to be elucidated.

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