A dedicated haem lyase is required for the maturation of a novel bacterial cytochrome c with unconventional covalent haem binding.
In bacterial c-type cytochromes, the haem cofactor is covalently attached via two cysteine residues organized in a haem c-binding motif. Here, a novel octa-haem c protein, MccA, is described that contains only seven conventional haem c-binding motifs (CXXCH), in addition to several single cysteine residues and a conserved CH signature. Mass spectrometric analysis of purified MccA from Wolinella succinogenes suggests that two of the single cysteine residues are actually part of an unprecedented CX15CH sequence involved in haem c binding. Spectroscopic characterization of MccA identified an unusual high-potential haem c with a red-shifted absorption maximum, not unlike that of certain eukaryotic cytochromes c that exceptionally bind haem via only one thioether bridge. A haem lyase gene was found to be specifically required for the maturation of MccA in W. succinogenes. Equivalent haem lyase-encoding genes belonging to either the bacterial cytochrome c biogenesis system I or II are present in the vicinity of every known mccA gene suggesting a dedicated cytochrome c maturation pathway. The results necessitate reconsideration of computer-based prediction of putative haem c-binding motifs in bacterial proteomes.
Hartshorne
Robert S
RS
School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK.
Kern
Melanie
M
Meyer
Björn
B
Clarke
Thomas A
TA
Karas
Michael
M
Richardson
David J
DJ
Simon
Jörg
J
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001665:Binding Sites; D045304:Cytochromes c / Q000378:metabolism*; D006418:Heme / Q000378:metabolism*; D008190:Lyases / Q000737:chemistry / Q000302:isolation & purification / Q000502:physiology*; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D016968:Wolinella / Q000201:enzymology*
D006418:Heme; D045304:Cytochromes c; D008190:Lyases