Extracytoplasmic prosthetic group ligation to apoproteins: maturation of c ‐type cytochromes

Summary In all organisms, haem is post‐translationally and covalently attached to c apocytochromes to produce c holocytochromes via a process called c ‐type cytochromes maturation, which involves numerous components. In bacteria it was not clear which of these components catalyses the extracytoplasmic haem–apocytochrome ligation per se . In this issue of Molecular Microbiology , Feissner and colleagues report that a single polypeptide from Helicobacter pylori , corresponding to the fusion of two proteins found in other organisms, performs haem ligation to a coexpressed Bordetella pertussis apocytochrome c in an Escherichia coli mutant lacking its own cytochrome c maturation proteins. This simple experimental system pinpoints the components catalysing extracytoplasmic covalent haem ligation and raises intriguing issues about the requirements for delivery of haem and apocytochrome c substrates to produce c holocytochromes.