An Escherichia coli ccm (cytochrome c maturation) deletion strain substantially expresses Hydrogenobacter thermophilus cytochrome c552 in the cytoplasm: availability of haem influences cytochrome c552 maturation

Abstract

The maturation of Hydrogenobacter thermophilus cytochrome c 552 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 c 552 has sufficient tertiary structure to allow the haem to slot into its binding pocket, which in turn triggers the spontaneous covalent attachment between apocytochrome c 552 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 c 552 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 c 552 biogenesis that occurs in a reference strain following supplementation of growth media with δ-aminolevulinic acid.