title: Reductive activation and structural rearrangement in superoxide reductase: a combined infrared spectroscopic and computational study.
abstract: Superoxide reductases (SOR) are a family of non-heme iron enzymes that limit oxidative stress by catalysing the reduction of superoxide to hydrogen peroxide and, thus, represent model systems for the detoxification of reactive oxygen species. In several enzymes of this type, reductive activation of the active site involves the reversible dissociation of a glutamate from the proposed substrate binding site at the iron. In this study we have employed IR spectroscopic and theoretical methods to gain insights into redox-linked structural changes of 1Fe-type superoxide reductases, focusing on the enzyme from the archaeon Ignicoccus hospitalis. Guided by crystal structure data and complemented by spectra calculation for an active site model, the main IR difference signals could be assigned. These signals reflect redox-induced structural changes in the first coordination sphere of the iron centre, adjacent loop and helical regions, and more remote β-sheets. By comparison with the spectra obtained for the E23A mutant of Ignicoccus hospitalis SOR, it is shown that glutamate E23 dissociates reversibly from the ferrous iron during reductive activation of the wild type enzyme. Moreover, this process is found to trigger a global conformational transition of the protein that is strictly dependent on the presence of E23. Similar concerted structural changes can be inferred from the IR spectra of related SORs such as that from Archaeoglobus fulgidus, indicating a widespread mechanism. A possible functional role of this process in terms of synergistic effects during reductive activation of the homotetrameric enzyme is proposed.
authors.affiliation: Technische Universität Berlin, Institut für Chemie, Sekr. PC14, Straße des 17. Juni 135, 10623 Berlin, Germany. marius.horch@gmx.de ingo.zebger@tu-berlin.de.
authors.forename: M
authors.initials: M
authors.lastname: Horch
authors.forename: A F
authors.initials: AF
authors.lastname: Pinto
authors.forename: T
authors.initials: T
authors.lastname: Utesch
authors.forename: M A
authors.initials: MA
authors.lastname: Mroginski
authors.forename: C V
authors.initials: CV
authors.lastname: Romão
authors.forename: M
authors.initials: M
authors.lastname: Teixeira
authors.forename: P
authors.initials: P
authors.lastname: Hildebrandt
authors.forename: I
authors.initials: I
authors.lastname: Zebger
mesh_terms: D003198:Computer Simulation; D004789:Enzyme Activation; D008956:Models, Chemical; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000648:ultrastructure*; D011487:Protein Conformation; D013055:Spectrophotometry, Infrared / Q000379:methods*
chemical_list: D010088:Oxidoreductases; C121849:superoxide reductase