title: Crystal structure and desulfurization mechanism of 2'-hydroxybiphenyl-2-sulfinic acid desulfinase.
abstract: The desulfurization of dibenzothiophene in Rhodococcus erythropolis is catalyzed by two monooxygenases, DszA and DszC, and a desulfinase, DszB. In the last step of this pathway, DszB hydrolyzes 2'-hydroxybiphenyl-2-sulfinic acid into 2-hydroxybiphenyl and sulfite. We report on the crystal structures of DszB and an inactive mutant of DszB in complex with substrates at resolutions of 1.8A or better. The overall fold of DszB is similar to those of periplasmic substrate-binding proteins. In the substrate complexes, biphenyl rings of substrates are recognized by extensive hydrophobic interactions with the active site residues. Binding of substrates accompanies structural changes of the active site loops and recruits His(60) to the active site. The sulfinate group of bound substrates forms hydrogen bonds with side chains of Ser(27), His(60), and Arg(70), each of which is shown by site-directed mutagenesis to be essential for the activity. In our proposed reaction mechanism, Cys(27) functions as a nucleophile and seems to be activated by the sulfinate group of substrates, whereas His(60) and Arg(70) orient the syn orbital of sulfinate oxygen to the sulfhydryl hydrogen of Cys(27) and stabilize the negatively charged reaction intermediate. Cys, His, and Arg residues are conserved in putative proteins homologous to DszB, which are presumed to constitute a new family of desulfinases.
authors.affiliation: Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyoku, Tokyo 113-8657.
authors.forename: Woo Cheol
authors.initials: WC
authors.lastname: Lee
authors.forename: Takashi
authors.initials: T
authors.lastname: Ohshiro
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Matsubara
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Izumi
authors.forename: Masaru
authors.initials: M
authors.lastname: Tanokura
mesh_terms: D000085:Acetates / Q000737:chemistry; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001120:Arginine / Q000378:metabolism; D001665:Binding Sites; D018360:Crystallography, X-Ray; D005990:Glycerol / Q000737:chemistry; D006639:Histidine / Q000378:metabolism; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D008969:Molecular Sequence Data; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D011485:Protein Binding; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012240:Rhodococcus / Q000201:enzymology; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000378:metabolism; D013379:Substrate Specificity; D013441:Sulfinic Acids / Q000737:chemistry*; D013455:Sulfur / Q000378:metabolism*; D013876:Thiophenes / Q000737:chemistry / Q000378:metabolism; D014867:Water / Q000737:chemistry
chemical_list: D000085:Acetates; D013441:Sulfinic Acids; D013876:Thiophenes; D014867:Water; D012694:Serine; D006639:Histidine; D013455:Sulfur; D001120:Arginine; D050862:Oxidoreductases Acting on Sulfur Group Donors; D005990:Glycerol; C016366:dibenzothiophene