title: Structure of the molybdenum site in YedY, a sulfite oxidase homologue from Escherichia coli.
abstract: YedY from Escherichia coli is a new member of the sulfite oxidase family of molybdenum cofactor (Moco)-containing oxidoreductases. We investigated the atomic structure of the molybdenum site in YedY by X-ray absorption spectroscopy, in comparison to human sulfite oxidase (hSO) and to a Mo(IV) model complex. The K-edge energy was indicative of Mo(V) in YedY, in agreement with X- and Q-band electron paramagnetic resonance results, whereas the hSO protein contained Mo(VI). In YedY and hSO, molybdenum is coordinated by two sulfur ligands from the molybdopterin ligand of the Moco, one thiolate sulfur of a cysteine (average Mo-S bond length of ∼2.4 Å), and one (axial) oxo ligand (Mo═O, ∼1.7 Å). hSO contained a second oxo group at Mo as expected, but in YedY, two species in about a 1:1 ratio were found at the active site, corresponding to an equatorial Mo-OH bond (∼2.1 Å) or possibly to a shorter Mo-O(-) bond. Yet another oxygen (or nitrogen) at a ∼2.6 Å distance to Mo in YedY was identified, which could originate from a water molecule in the substrate binding cavity or from an amino acid residue close to the molybdenum site, i.e., Glu104, that is replaced by a glycine in hSO, or Asn45. The addition of the poor substrate dimethyl sulfoxide to YedY left the molybdenum coordination unchanged at high pH. In contrast, we found indications that the better substrate trimethylamine N-oxide and the substrate analogue acetone were bound at a ∼2.6 Å distance to the molybdenum, presumably replacing the equatorial oxygen ligand. These findings were used to interpret the recent crystal structure of YedY and bear implications for its catalytic mechanism.
authors.affiliation: Institut für Experimentalphysik, Freie Universität Berlin, Berlin, Germany.
authors.forename: Kajsa G V
authors.initials: KG
authors.lastname: Havelius
authors.forename: Stefan
authors.initials: S
authors.lastname: Reschke
authors.forename: Sebastian
authors.initials: S
authors.lastname: Horn
authors.forename: Alexander
authors.initials: A
authors.lastname: Döring
authors.forename: Dimitri
authors.initials: D
authors.lastname: Niks
authors.forename: Russ
authors.initials: R
authors.lastname: Hille
authors.forename: Carola
authors.initials: C
authors.lastname: Schulzke
authors.forename: Silke
authors.initials: S
authors.lastname: Leimkühler
authors.forename: Michael
authors.initials: M
authors.lastname: Haumann
mesh_terms: D020134:Catalytic Domain; D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli / Q000737:chemistry / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000737:chemistry*; D006801:Humans; D008982:Molybdenum / Q000737:chemistry*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry*; D050876:Sulfite Oxidase / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D029968:Escherichia coli Proteins; D008982:Molybdenum; D010088:Oxidoreductases; C495992:YedY protein, E coli; D050876:Sulfite Oxidase