title: Quinol-cytochrome c oxidoreductase and cytochrome c4 mediate electron transfer during selenate respiration in Thauera selenatis.
abstract: Selenate reductase (SER) from Thauera selenatis is a periplasmic enzyme that has been classified as a type II molybdoenzyme. The enzyme comprises three subunits SerABC, where SerC is an unusual b-heme cytochrome. In the present work the spectropotentiometric characterization of the SerC component and the identification of redox partners to SER are reported. The mid-point redox potential of the b-heme was determined by optical titration (E(m) + 234 +/- 10 mV). A profile of periplasmic c-type cytochromes expressed in T. selenatis under selenate respiring conditions was undertaken. Two c-type cytochromes were purified ( approximately 24 and approximately 6 kDa), and the 24-kDa protein (cytc-Ts4) was shown to donate electrons to SerABC in vitro. Protein sequence of cytc-Ts4 was obtained by N-terminal sequencing and liquid chromatography-tandem mass spectrometry analysis, and based upon sequence similarities, was assigned as a member of cytochrome c(4) family. Redox potentiometry, combined with UV-visible spectroscopy, showed that cytc-Ts4 is a diheme cytochrome with a redox potential of +282 +/- 10 mV, and both hemes are predicted to have His-Met ligation. To identify the membrane-bound electron donors to cytc-Ts4, growth of T. selenatis in the presence of respiratory inhibitors was monitored. The specific quinol-cytochrome c oxidoreductase (QCR) inhibitors myxothiazol and antimycin A partially inhibited selenate respiration, demonstrating that some electron flux is via the QCR. Electron transfer via a QCR and a diheme cytochrome c(4) is a novel route for a member of the DMSO reductase family of molybdoenzymes.
authors.affiliation: School of Biosciences, Centre for Biocatalysis, University of Exeter, Stocker Road, Exeter EX4 4QD, United Kingdom.
authors.forename: Elisabeth C
authors.initials: EC
authors.lastname: Lowe
authors.forename: Sarah
authors.initials: S
authors.lastname: Bydder
authors.forename: Robert S
authors.initials: RS
authors.lastname: Hartshorne
authors.forename: Hannah L U
authors.initials: HL
authors.lastname: Tape
authors.forename: Elizabeth J
authors.initials: EJ
authors.lastname: Dridge
authors.forename: Charles M
authors.initials: CM
authors.lastname: Debieux
authors.forename: Konrad
authors.initials: K
authors.lastname: Paszkiewicz
authors.forename: Ian
authors.initials: I
authors.lastname: Singleton
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Lewis
authors.forename: Joanne M
authors.initials: JM
authors.lastname: Santini
authors.forename: David J
authors.initials: DJ
authors.lastname: Richardson
authors.forename: Clive S
authors.initials: CS
authors.lastname: Butler
mesh_terms: D000968:Antimycin A / Q000737:chemistry; D003574:Cytochrome c Group / Q000737:chemistry*; D003580:Cytochromes / Q000737:chemistry; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000737:chemistry*; D004583:Electrons; D006873:Hydroquinones / Q000737:chemistry*; D008689:Methacrylates / Q000737:chemistry; D008954:Models, Biological; D008956:Models, Chemical; D008958:Models, Molecular; D010084:Oxidation-Reduction; D012643:Selenium / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D020628:Thauera / Q000378:metabolism*; D013844:Thiazoles / Q000737:chemistry
chemical_list: D003574:Cytochrome c Group; D003580:Cytochromes; D006873:Hydroquinones; D008689:Methacrylates; D013844:Thiazoles; C034186:cytochrome C4; D000968:Antimycin A; C030517:myxothiazol; D003576:Electron Transport Complex IV; D012643:Selenium
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