title: Structure-activity characterization of sulfide:quinone oxidoreductase variants.
abstract: Sulfide:quinone oxidoreductase (SQR) is a peripheral membrane protein that catalyzes the oxidation of sulfide species to elemental sulfur. The enzymatic reaction proceeds in two steps. The electrons from sulfides are transferred first to the enzyme cofactor, FAD, which, in turn, passes them onto the quinone pool in the membrane. Several wild-type SQR structures have been reported recently. However, the enzymatic mechanism of SQR has not been fully delineated. In order to understand the role of the catalytically essential residues in the enzymatic mechanism of SQR we produced a number of variants of the conserved residues in the catalytic site including the cysteine triad of SQR from the acidophilic, chemolithotrophic bacterium Acidithiobacillus ferrooxidans. These were structurally characterized and their activities for each reaction step were determined. In addition, the crystal structures of the wild-type SQR with sodium selenide and gold(I) cyanide have been determined. Previously we proposed a mechanism for the reduction of sulfides to elemental sulfur involving nucleophilic attack of Cys356 on C(4A) atom of FAD. Here we also consider an alternative anionic radical mechanism by direct electron transfer from Cys356 to the isoalloxazine ring of FAD.
authors.affiliation: Department of Biochemistry, School of Translational Medicine, Faculty of Medicine and Dentistry, University of Alberta, 4-020J Katz Centre for Pharmacy and Health Research, Edmonton, Alberta, Canada T6G 2H7.
authors.forename: Maia M
authors.initials: MM
authors.lastname: Cherney
authors.forename: Yanfei
authors.initials: Y
authors.lastname: Zhang
authors.forename: Michael N G
authors.initials: MN
authors.lastname: James
authors.forename: Joel H
authors.initials: JH
authors.lastname: Weiner
mesh_terms: D042763:Acidithiobacillus / Q000378:metabolism*; D018360:Crystallography, X-Ray; D005182:Flavin-Adenine Dinucleotide / Q000378:metabolism; D006862:Hydrogen Sulfide / Q000378:metabolism; D010084:Oxidation-Reduction; D011808:Quinone Reductases / Q000737:chemistry* / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D005182:Flavin-Adenine Dinucleotide; D011808:Quinone Reductases; C073412:sulfide quinone reductase; D006862:Hydrogen Sulfide