title: Study on dioxygen reduction by mutational modifications of the hydrogen bond network leading from bulk water to the trinuclear copper center in bilirubin oxidase.
abstract: The hydrogen bond network leading from bulk water to the trinuclear copper center in bilirubin oxidase is constructed with Glu463 and water molecules to transport protons for the four-electron reduction of dioxygen. Substitutions of Glu463 with Gln or Ala were attributed to virtually complete loss or significant reduction in enzymatic activities due to an inhibition of the proton transfer steps to dioxygen. The single turnover reaction of the Glu463Gln mutant afforded the highly magnetically interacted intermediate II (native intermediate) with a broad g=1.96 electron paramagnetic resonance signal detectable at cryogenic temperatures. Reactions of the double mutants, Cys457Ser/Glu463Gln and Cys457Ser/Glu463Ala afforded the intermediate I (peroxide intermediate) because the type I copper center to donate the fourth electron to dioxygen was vacant in addition to the interference of proton transport due to the mutation at Glu463. The intermediate I gave no electron paramagnetic resonance signal, but the type II copper signal became detectable with the decay of the intermediate I. Structural and functional similarities between multicopper oxidases are discussed based on the present mutation at Glu463 in bilirubin oxidase.
authors: Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan.
authors: Hirotoshi
authors: H
authors: Morishita
authors: Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan.
authors: Daisuke
authors: D
authors: Kurita
authors: Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan.
authors: Kunishige
authors: K
authors: Kataoka
authors: Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan. Electronic address: tsakurai@se.kanazawa-u.ac.jp.
authors: Takeshi
authors: T
authors: Sakurai
mesh_terms: D001665:Binding Sites; D003300:Copper / Q000737:chemistry*; D004789:Enzyme Activation; D018698:Glutamic Acid / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D006860:Hydrogen Bonding; D016297:Mutagenesis, Site-Directed / Q000379:methods*; D010084:Oxidation-Reduction; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000737:chemistry* / Q000235:genetics; D011485:Protein Binding; D013329:Structure-Activity Relationship; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D018698:Glutamic Acid; D003300:Copper; D006859:Hydrogen; D044925:Oxidoreductases Acting on CH-CH Group Donors; C042401:bilirubin oxidase
keywords: Bilirubin oxidase; Dioxygen reduction; Hydrogen bond network; Multicopper oxidase