title: A tryptophan neutral radical in the oxidized state of versatile peroxidase from Pleurotus eryngii: a combined multifrequency EPR and density functional theory study.
abstract: Versatile peroxidases are heme enzymes that combine catalytic properties of lignin peroxidases and manganese peroxidases, being able to oxidize Mn(2+) as well as phenolic and non-phenolic aromatic compounds in the absence of mediators. The catalytic process (initiated by hydrogen peroxide) is the same as in classical peroxidases, with the involvement of 2 oxidizing equivalents and the formation of the so-called Compound I. This latter state contains an oxoferryl center and an organic cation radical that can be located on either the porphyrin ring or a protein residue. In this study, a radical intermediate in the reaction of versatile peroxidase from the ligninolytic fungus Pleurotus eryngii with H(2)O(2) has been characterized by multifrequency (9.4 and 94 GHz) EPR and assigned to a tryptophan residue. Comparison of experimental data and density functional theory theoretical results strongly suggests the assignment to a tryptophan neutral radical, excluding the assignment to a tryptophan cation radical or a histidine radical. Based on the experimentally determined side chain orientation and comparison with a high resolution crystal structure, the tryptophan neutral radical can be assigned to Trp(164) as the site involved in long-range electron transfer for aromatic substrate oxidation.
authors.affiliation: Department of Chemistry, University of Siena, 53100 Siena, Italy. pogni@unisi.it
authors.forename: Rebecca
authors.initials: R
authors.lastname: Pogni
authors.forename: M Camilla
authors.initials: MC
authors.lastname: Baratto
authors.forename: Christian
authors.initials: C
authors.lastname: Teutloff
authors.forename: Stefania
authors.initials: S
authors.lastname: Giansanti
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Ruiz-Dueñas
authors.forename: Thomas
authors.initials: T
authors.lastname: Choinowski
authors.forename: Klaus
authors.initials: K
authors.lastname: Piontek
authors.forename: Angel T
authors.initials: AT
authors.lastname: Martínez
authors.forename: Friedhelm
authors.initials: F
authors.lastname: Lendzian
authors.forename: Riccardo
authors.initials: R
authors.lastname: Basosi
mesh_terms: D002384:Catalysis; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D006861:Hydrogen Peroxide / Q000737:chemistry*; D008345:Manganese / Q000378:metabolism; D008962:Models, Theoretical; D016877:Oxidants / Q000737:chemistry; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000737:chemistry* / Q000378:metabolism*; D020076:Pleurotus / Q000201:enzymology*; D014364:Tryptophan
chemical_list: D005609:Free Radicals; D016877:Oxidants; D008345:Manganese; D014364:Tryptophan; D006861:Hydrogen Peroxide; D010544:Peroxidases