title: Novel thioether bond revealed by a 1.7 A crystal structure of galactose oxidase.
abstract: Galactose oxidase is an extracellular enzyme secreted by the fungus Dactylium dendroides. It is monomeric, with a relative molecular mass of 68,000, catalyses the stereospecific oxidation of a broad range of primary alcohol substrates and possesses a unique mononuclear copper site essential for catalysing a two-electron transfer reaction during the oxidation of primary alcohols to corresponding aldehydes. Recent evidence arguing against a Cu(III)-Cu(I) couple implies the existence of a second redox-active site proposed to involve pyrroloquinoline quinone or a tyrosine radical. We now report the crystal structure of galactose oxidase at 1.7 A resolution. This reveals a unique structural feature at the copper site with a novel thioether bond linking Cys 228 and Tyr 272 in a stacking interaction with Trp 290. We propose that these molecular components stabilize the protein free-radical species essential for catalysis and thus provide a 'built-in' secondary cofactor. This feature may represent a new mechanism for mediating electron transfer in metalloenzymes in the absence of exogenous cofactors.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Leeds, UK.
authors.forename: N
authors.initials: N
authors.lastname: Ito
authors.forename: S E
authors.initials: SE
authors.lastname: Phillips
authors.forename: C
authors.initials: C
authors.lastname: Stevens
authors.forename: Z B
authors.initials: ZB
authors.lastname: Ogel
authors.forename: M J
authors.initials: MJ
authors.lastname: McPherson
authors.forename: J N
authors.initials: JN
authors.lastname: Keen
authors.forename: K D
authors.initials: KD
authors.lastname: Yadav
authors.forename: P F
authors.initials: PF
authors.lastname: Knowles
mesh_terms: D001665:Binding Sites; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003300:Copper / Q000737:chemistry; D003460:Crystallization; D005609:Free Radicals; D005658:Fungi / Q000201:enzymology; D005692:Galactose Oxidase / Q000737:chemistry*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011487:Protein Conformation; D014443:Tyrosine; D014961:X-Ray Diffraction
chemical_list: D005609:Free Radicals; D014443:Tyrosine; D003300:Copper; D005692:Galactose Oxidase