Dispensable residues in the active site of the cytochrome c biogenesis protein CcmH

Robertson, Ian B.; Stevens, Julie M.; Ferguson, Stuart J.

doi:10.1016/j.febslet.2008.07.052

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Volume 582, Issue 20 , Pages 3067-3072, 3 September 2008

Dispensable residues in the active site of the cytochrome c biogenesis protein CcmH

Edited by Peter Brzezinski

Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom

Received 12 June 2008; received in revised form 27 July 2008; accepted 28 July 2008. published online 05 August 2008.

Abstract

CcmH functions in the assembly of c-type cytochromes in the Escherichia coli periplasm. The conserved cysteine pair in the N-terminal of its two membrane-anchored periplasmic domains is thought to reduce the CXXCH motif of cytochromes c. The recent structure of Pseudomonas aeruginosa CcmH identified conserved residues that might be functionally important. We replaced with alanine the active-site cysteines of E. coli CcmH, as well as R42, S54, R63, and tested the effects on cytochrome c production anaerobically and aerobically. Unexpectedly, replacement of the conserved non-cysteine active-site residues had little effect, whilst the cysteines were required under aerobic, but not anaerobic, conditions. We confirmed that removal of the C-terminal tetratricopeptide-like domain does not, surprisingly, abolish assembly of cytochromes c.

Abbreviations: Ccm, cytochrome c maturation, TPR, tetratricopeptide repeat

Keywords: Cytochrome c maturation, CcmH, Thiol-disulphide oxidoreductase