title: New spectroscopic and electrochemical insights on a class I superoxide reductase: evidence for an intramolecular electron-transfer pathway.
abstract: SORs (superoxide reductases) are enzymes involved in bacterial resistance to reactive oxygen species, catalysing the reduction of superoxide anions to hydrogen peroxide. So far three structural classes have been identified. Class I enzymes have two iron-centre-containing domains. Most studies have focused on the catalytic iron site (centre II), yet the role of centre I is poorly understood. The possible roles of this iron site were approached by an integrated study using both classical and fast kinetic measurements, as well as direct electrochemistry. A new heterometallic form of the protein with a zinc-substituted centre I, maintaining the iron active-site centre II, was obtained, resulting in a stable derivative useful for comparison with the native all-iron from. Second-order rate constants for the electron transfer between reduced rubredoxin and the different SOR forms were determined to be 2.8 × 10⁷ M⁻¹ · s⁻¹ and 1.3 × 10⁶ M⁻¹ · s⁻¹ for SORFe(IIII)-Fe(II) and for SORFe(IIII)-Fe(III) forms respectively, and 3.2 × 10⁶ M⁻¹ · s⁻¹ for the SORZn(II)-Fe(III) form. The results obtained seem to indicate that centre I transfers electrons from the putative physiological donor rubredoxin to the catalytic active iron site (intramolecular process). In addition, electrochemical results show that conformational changes are associated with the redox state of centre I, which may enable a faster catalytic response towards superoxide anion. The apparent rate constants calculated for the SOR-mediated electron transfer also support this observation.
authors.affiliation: REQUIMTE/CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal.
authors.forename: Filipe
authors.initials: F
authors.lastname: Folgosa
authors.forename: Cristina M
authors.initials: CM
authors.lastname: Cordas
authors.forename: Joana A
authors.initials: JA
authors.lastname: Santos
authors.forename: Alice S
authors.initials: AS
authors.lastname: Pereira
authors.forename: José J G
authors.initials: JJ
authors.lastname: Moura
authors.forename: Pedro
authors.initials: P
authors.lastname: Tavares
authors.forename: Isabel
authors.initials: I
authors.lastname: Moura
mesh_terms: D016969:Desulfovibrio vulgaris / Q000201:enzymology / Q000378:metabolism; D004563:Electrochemistry; D004579:Electron Transport; D007501:Iron / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D017382:Reactive Oxygen Species; D012416:Rubredoxins / Q000737:chemistry / Q000378:metabolism; D013482:Superoxide Dismutase / Q000737:chemistry / Q000378:metabolism; D013481:Superoxides / Q000737:chemistry / Q000378:metabolism
chemical_list: D017382:Reactive Oxygen Species; D012416:Rubredoxins; D013481:Superoxides; D007501:Iron; D010088:Oxidoreductases; C121849:superoxide reductase; D013482:Superoxide Dismutase