title: Low-spin heme A in the heme A biosynthetic protein CtaA from Bacillus subtilis.
abstract: Synthesis of heme A from heme B (protoheme IX) most likely occurs in two steps with heme O as an intermediate. Bacillus subtilis CtaB, an integral membrane protein, functions in farnesylation of heme B to form heme O. CtaA, also a membrane protein, is required for heme A synthesis from heme O and appears to be a monooxygenase and/or a dehydrogenase. Wild-type ctaA and ctaB expressed together from plasmids in B. subtilis resulted in CtaA containing equimolar amounts of low-spin heme B and heme A; this form of CtaA was named cyt ba-CTA. A mutant ctaB gene was identified and characterised. It encodes a truncated CtaB polypeptide. Wild-type ctaA and the mutant ctaB gene on plasmids resulted in CtaA containing mainly low-spin heme B; this variant was named cyt b-CTA. The heme B component in cyt ba-CTA and cyt b-CTA showed identical properties; a mid-point redox potential of +85 mV, an EPR g(max) signal at 3.7, and a split alpha-band light absorption peak. The heme A component in cyt ba-CTA showed a mid-point potential of +242 mV, an EPR g(max) signal at 3.5, and the alpha-band light absorption peak at 585 nm. It is suggested that the CtaA protein contains two heme binding sites, one for heme B and one for substrate heme. The heme B would play a role in electron transfer, i.e. function as a cytochrome, in the monooxygenase and/or dehydrogenase reaction catalysed by CtaA whereas heme O/heme A would be substrate/product.
authors.affiliation: Department of Microbiology, Lund University, Sweden.
authors.forename: B
authors.initials: B
authors.lastname: Svensson
authors.forename: K K
authors.initials: KK
authors.lastname: Andersson
authors.forename: L
authors.initials: L
authors.lastname: Hederstedt
mesh_terms: D001412:Bacillus subtilis / Q000201:enzymology*; D001426:Bacterial Proteins; D001483:Base Sequence; D017936:Cytochrome a Group / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D003573:Cytochrome b Group / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics*; D004578:Electron Spin Resonance Spectroscopy; D006418:Heme / Q000096:biosynthesis / Q000737:chemistry*; D008565:Membrane Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids / Q000737:chemistry / Q000235:genetics; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D013057:Spectrum Analysis / Q000379:methods; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; C090098:CtaA protein, bacteria; D017936:Cytochrome a Group; D003573:Cytochrome b Group; D008565:Membrane Proteins; D011994:Recombinant Proteins; D006418:Heme