title: Dispensable residues in the active site of the cytochrome c biogenesis protein CcmH.
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.
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK.
authors.forename: Ian B
authors.initials: IB
authors.lastname: Robertson
authors.forename: Julie M
authors.initials: JM
authors.lastname: Stevens
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Ferguson
mesh_terms: D000332:Aerobiosis; D000409:Alanine / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D017124:Conserved Sequence; D003545:Cysteine / Q000235:genetics / Q000378:metabolism; D045304:Cytochromes c / Q000096:biosynthesis*; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary
chemical_list: D001425:Bacterial Outer Membrane Proteins; C451399:CcmH protein, E coli; D029968:Escherichia coli Proteins; D045304:Cytochromes c; D003545:Cysteine; D000409:Alanine