title: DFT investigation of the molybdenum cofactor in periplasmic nitrate reductases: structure of the Mo(V) EPR-active species.
abstract: The periplasmic nitrate reductase NAP belongs to the DMSO reductase family that regroups molybdoenzymes housing a bis-molybdopterin cofactor as the active site. Several forms of the Mo(V) state, an intermediate redox state in the catalytic cycle of the enzyme, have been evidenced by EPR spectroscopy under various conditions, but their structure and catalytic relevance are not fully understood. On the basis of structural data available from the literature, we built several models that reproduce the first coordination sphere of the molybdenum cofactor and used DFT methods to make magneto-structural correlations on EPR-detected species. "High-g" states, which are the most abundant Mo(V) species, are characterized by a low-anisotropy g tensor and a high g(min) value. We assign this signature to a six-sulfur coordination sphere in a pseudotrigonal prismatic geometry with a partial disulfide bond. The "very high-g" species is well described with a sulfido ion as the sixth ligand. The "low-g" signal can be successfully associated to a Mo(V) sulfite-oxidase-type active site with only one pterin moiety coordinated to the molybdenum ion with an oxo or sulfido axial ligand. For all these species we investigate their catalytic activity using a thermodynamic point of view on the molybdenum coordination sphere. Beyond the periplasmic nitrate reductase case, this work provides useful magneto-structural correlations to characterize EPR-detected species in mononuclear molybdoenzymes.
authors.affiliation: Unité de Bioénergétique et Ingénierie des Protéines, UMR 7281, Centre National de la Recherche Scientifique, Institut de Microbiologie de la Méditerranée, and Aix-Marseille University, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France. fbiaso@imm.cnrs.fr
authors.forename: Frédéric
authors.initials: F
authors.lastname: Biaso
authors.forename: Bénédicte
authors.initials: B
authors.lastname: Burlat
authors.forename: Bruno
authors.initials: B
authors.lastname: Guigliarelli
mesh_terms: D003067:Coenzymes / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D008667:Metalloproteins / Q000737:chemistry*; D008958:Models, Molecular; D000090006:Molybdenum Cofactors; D009565:Nitrate Reductases / Q000737:chemistry*; D010084:Oxidation-Reduction; D019897:Periplasm / Q000201:enzymology*; D011621:Pteridines / Q000737:chemistry*
chemical_list: D003067:Coenzymes; D008667:Metalloproteins; D000090006:Molybdenum Cofactors; D009565:Nitrate Reductases; D011621:Pteridines; C022261:molybdopterin