title: Electrochemical evidence that pyranopterin redox chemistry controls the catalysis of YedY, a mononuclear Mo enzyme.
abstract: A long-standing contradiction in the field of mononuclear Mo enzyme research is that small-molecule chemistry on active-site mimic compounds predicts ligand participation in the electron transfer reactions, but biochemical measurements only suggest metal-centered catalytic electron transfer. With the simultaneous measurement of substrate turnover and reversible electron transfer that is provided by Fourier-transformed alternating-current voltammetry, we show that Escherichia coli YedY is a mononuclear Mo enzyme that reconciles this conflict. In YedY, addition of three protons and three electrons to the well-characterized "as-isolated" Mo(V) oxidation state is needed to initiate the catalytic reduction of either dimethyl sulfoxide or trimethylamine N-oxide. Based on comparison with earlier studies and our UV-vis redox titration data, we assign the reversible one-proton and one-electron reduction process centered around +174 mV vs. standard hydrogen electrode at pH 7 to a Mo(V)-to-Mo(IV) conversion but ascribe the two-proton and two-electron transition occurring at negative potential to the organic pyranopterin ligand system. We predict that a dihydro-to-tetrahydro transition is needed to generate the catalytically active state of the enzyme. This is a previously unidentified mechanism, suggested by the structural simplicity of YedY, a protein in which Mo is the only metal site.
authors.affiliation: Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom;
authors.forename: Hope
authors.initials: H
authors.lastname: Adamson
authors.affiliation: School of Chemistry, Monash University, Clayton, VIC 3800, Australia;
authors.forename: Alexandr N
authors.initials: AN
authors.lastname: Simonov
authors.affiliation: Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada.
authors.forename: Michelina
authors.initials: M
authors.lastname: Kierzek
authors.affiliation: Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Rothery
authors.affiliation: Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada.
authors.forename: Joel H
authors.initials: JH
authors.lastname: Weiner
authors.affiliation: School of Chemistry, Monash University, Clayton, VIC 3800, Australia;
authors.forename: Alan M
authors.initials: AM
authors.lastname: Bond
authors.affiliation: Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom; alison.parkin@york.ac.uk.
authors.forename: Alison
authors.identifier: http://orcid.org/0000-0003-4715-7200
authors.initials: A
authors.lastname: Parkin
mesh_terms: D002384:Catalysis; D020134:Catalytic Domain; D004563:Electrochemistry; D029968:Escherichia coli Proteins / Q000737:chemistry*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry*; D011622:Pterins / Q000737:chemistry*
chemical_list: D029968:Escherichia coli Proteins; D011622:Pterins; C490076:pyranopterin; D010088:Oxidoreductases; C495992:YedY protein, E coli
keywords: Fourier-transformed alternating-current voltammetry; YedY; mononuclear molybdenum enzyme; protein film electrochemistry; pyranopterin