title: S K-edge X-ray absorption spectroscopic investigation of the Ni-containing superoxide dismutase active site: new structural insight into the mechanism.
abstract: Superoxide dismutases protect cells from the toxic effects of reactive oxygen species derived from superoxide. Nickel-containing superoxide dismutases (NiSOD), found in Streptomyces species and in cyanobacteria, are distinct from Mn-, Fe-, or Cu/Zn-containing SODs in amino acid sequence and metal ligand environment. Sulfur K-edge X-ray absorption spectroscopic investigations were carried out for a series of mono- and binuclear Ni model compounds with varying sulfur ligation, and for oxidized and reduced NiSOD to elucidate the types of Ni-S interactions found in the two oxidation states. The S K-edge XAS spectra clearly indicate the presence of Ni(III)-bound terminal thiolate in the oxidized enzyme and the absence of such coordination to Ni(II) in the peroxide-reduced enzyme. This striking change in the S ligation for Ni with redox suggests that, upon peroxide reduction, an electron is transferred to the Ni(III) site and the terminal thiolate becomes protonated, providing an efficient mechanism for proton-coupled electron transfer.
authors.affiliation: Department of Chemistry, Stanford University, Stanford, California 94305, USA.
authors.forename: Robert K
authors.initials: RK
authors.lastname: Szilagyi
authors.forename: Peter A
authors.initials: PA
authors.lastname: Bryngelson
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Maroney
authors.forename: Britt
authors.initials: B
authors.lastname: Hedman
authors.forename: Keith O
authors.initials: KO
authors.lastname: Hodgson
authors.forename: Edward I
authors.initials: EI
authors.lastname: Solomon
mesh_terms: D001665:Binding Sites; D009532:Nickel / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D013052:Spectrometry, X-Ray Emission / Q000379:methods; D013302:Streptomyces / Q000201:enzymology; D013482:Superoxide Dismutase / Q000737:chemistry* / Q000378:metabolism
chemical_list: D009532:Nickel; D013482:Superoxide Dismutase