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Zhang Y, Qadri A, Weiner JH. The quinone-binding site ofAcidithiobacillus ferrooxidanssulfide: quinone oxidoreductase controls both sulfide oxidation and quinone reduction. Biochem Cell Biol 2016; 94:159-66. [DOI: 10.1139/bcb-2015-0097] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
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−1and 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.
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Affiliation(s)
- Yanfei Zhang
- 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
| | - Ali Qadri
- 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
| | - Joel H. Weiner
- 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
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