title: Comparing the substrate specificities of cytochrome c biogenesis Systems I and II: bioenergetics.
abstract: c-Type cytochromes require specific post-translational protein systems, which vary in different organisms, for the characteristic covalent attachment of heme to the cytochrome polypeptide. Cytochrome c biogenesis System II, found in chloroplasts and many bacteria, comprises four subunits, two of which (ResB and ResC) are the minimal functional unit. The ycf5 gene from Helicobacter pylori encodes a fusion of ResB and ResC. Heterologous expression of ResBC in Escherichia coli lacking its own biogenesis machinery allowed us to investigate the substrate specificity of System II. ResBC is able to attach heme to monoheme c-type cytochromes c(550) from Paracoccus denitrificans and c(552) from Hydrogenobacter thermophilus, both normally matured by System I. The production of holocytochrome is enhanced by the addition of exogenous reductant. Single-cysteine variants of these cytochromes were not efficiently matured by System II, but System I was able to produce detectable amounts of AXXCH variants; this adds to evidence that there is no obligate requirement for a disulfide-bonded intermediate for the latter c-type cytochrome biogenesis system. In addition, System II was able to mature an AXXAH-containing variant into a b-type cytochrome, with implications for both heme supply to the periplasm and substrate recognition by System II.
authors.affiliation: Department of Biochemistry, University of Oxford, Oxford, UK.
authors.forename: Alan D
authors.initials: AD
authors.lastname: Goddard
authors.forename: Julie M
authors.initials: JM
authors.lastname: Stevens
authors.forename: Arnaud
authors.initials: A
authors.lastname: Rondelet
authors.forename: Elena
authors.initials: E
authors.lastname: Nomerotskaia
authors.forename: James W A
authors.initials: JW
authors.lastname: Allen
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Ferguson
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism; D045304:Cytochromes c / Q000096:biosynthesis* / Q000235:genetics; D004734:Energy Metabolism; D029968:Escherichia coli Proteins / Q000378:metabolism; D016480:Helicobacter pylori / Q000235:genetics; D006418:Heme / Q000378:metabolism; D009097:Multienzyme Complexes / Q000378:metabolism*; D010231:Paracoccus denitrificans / Q000201:enzymology; D011499:Protein Processing, Post-Translational / Q000502:physiology; D013379:Substrate Specificity
chemical_list: D001425:Bacterial Outer Membrane Proteins; C451399:CcmH protein, E coli; D003574:Cytochrome c Group; D029968:Escherichia coli Proteins; D009097:Multienzyme Complexes; D006418:Heme; D045304:Cytochromes c; C022302:cytochrome C-552; C031732:cytochrome C-550