title: The quinone-binding site of Acidithiobacillus ferrooxidans sulfide: quinone oxidoreductase controls both sulfide oxidation and quinone reduction.
abstract: Sulfide:quinone oxidoreductase (SQR) is a peripheral membrane enzyme that catalyzes the oxidation of sulfide and the reduction of ubiquinone. Ubiquinone binds to a conserved hydrophobic domain and shuttles electrons from a noncovalent flavin adenine dinucleotide cofactor to the membrane-bound quinone pool. Utilizing the structure of decylubiquinone bound to Acidithiobacillus ferrooxidans SQR, we combined site-directed mutagenesis and kinetic approaches to analyze quinone binding. SQR can reduce both benzoquinones and naphthoquinones. The alkyl side-chain of ubiquinone derivatives enhances binding to SQR but limits the enzyme turnover. Pentachlorophenol and 2-n-heptyl-4-hydroxyquinoline-N-oxide are potent inhibitors of SQR with apparent inhibition constants (Ki) of 0.46 μmol·L(-1) and 0.58 μmol·L(-1), respectively. The highly conserved amino acids surrounding the quinone binding site play an important role in quinone reduction. The phenyl side-chains of Phe357 and Phe391 sandwich the benzoquinone head group and are critical for quinone binding. Importantly, conserved amino acids that define the ubiquinone-binding site also play an important role in sulfide oxidation/flavin reduction.
authors.affiliation: Membrane Protein Disease Research Group, Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada.|Membrane Protein Disease Research Group, Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada.
authors.forename: Yanfei
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Membrane Protein Disease Research Group, Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada.|Membrane Protein Disease Research Group, Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada.
authors.forename: Ali
authors.initials: A
authors.lastname: Qadri
authors.affiliation: Membrane Protein Disease Research Group, Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada.|Membrane Protein Disease Research Group, Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada.
authors.forename: Joel H
authors.initials: JH
authors.lastname: Weiner
mesh_terms: D042763:Acidithiobacillus / Q000737:chemistry*; D016227:Benzoquinones / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D010084:Oxidation-Reduction; D011808:Quinone Reductases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D013440:Sulfides / Q000737:chemistry / Q000378:metabolism*
chemical_list: D016227:Benzoquinones; D013440:Sulfides; C004532:quinone; D011808:Quinone Reductases
keywords: Quinone reduction; affinité de liaison; binding affinity; inhibiteurs de quinones; midpoint potential; potentiel de point milieu; quinone inhibitors; réduction de la quinone