AnEscherichia coli ccm(cytochromecmaturation) deletion strain substantially expressesHydrogenobacter thermophiluscytochromec552in the cytoplasm: availability of haem influences cytochromec552maturation

Abstract

The maturation of Hydrogenobacter thermophilus cytochrome c₅₅₂ in the cytoplasm of Escherichia coli is unique among bacterial c-type cytochromes. It is now shown to be matured in a strain lacking the whole set of ccm (cytochrome c maturation) genes that are normally required for c-type cytochrome biogenesis in E. coli. As this cytochrome is thermostable we propose that the apocytochrome c₅₅₂ has sufficient tertiary structure to allow the haem to slot into its binding pocket, which in turn triggers the spontaneous covalent attachment between apocytochrome c₅₅₂ and haem. The ccm deletion strain of E. coli, derived from a strain that synthesizes elevated levels of endogenous c-type cytochromes, also produces larger amounts of cytoplasmic H. thermophilus cytochrome c₅₅₂ than a reference strain. This implies that elevated production of c-type cytochromes is not a consequence of high activity of ccm genes but rather an enhanced ability to supply haem, a view that is supported by the increase in thermophilic cytochrome c₅₅₂ biogenesis that occurs in a reference strain following supplementation of growth media with δ-aminolevulinic acid.