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Assembling Cytochrome c

Cytochrome c is a small heme protein that is an essential component of oxidation. The maturation of bacterial cytochrome c occurs in the periplasm, where the apoprotein is co-valently linked to a heme group via reduction of two cysteines in the protein's heme binding motif. CcmH (cytochromes c maturation protein H) is one of the proteins that participate in thioreduction in this maturation pathway.

CcmH adopts a peculiar three-helix bundle fold.

In this Paper of the Week, Adele Di Matteo and colleagues present the 1.7 Å crystal structure of the soluble periplasmic domain of CcmH from Pseudomonas aeruginosa. The domain adopts a peculiar three-helix bundle fold that involves an unusual arrangement of active site cysteine residues that is different from that of all other thiol-oxidoreductases reported so far. From their structure and related functional data, the authors propose that cytochrome c biogenesis occurs in an assembly-line fashion in which reduced CcmH specifically recognizes, binds to, and reduces oxidized apocytochrome c via the formation of a mixed disulfide complex.

FOOTNOTES

See referenced article, J. Biol. Chem. 2007, 282, 27012-27019

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