A tryptophan neutral radical in the oxidized state of versatile peroxidase from Pleurotus eryngii: a combined multifrequency EPR and density functional theory study.
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.
Pogni
Rebecca
R
Department of Chemistry, University of Siena, 53100 Siena, Italy. pogni@unisi.it
Baratto
M Camilla
MC
Teutloff
Christian
C
Giansanti
Stefania
S
Ruiz-Dueñas
Francisco J
FJ
Choinowski
Thomas
T
Piontek
Klaus
K
Martínez
Angel T
AT
Lendzian
Friedhelm
F
Basosi
Riccardo
R
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
D005609:Free Radicals; D016877:Oxidants; D008345:Manganese; D014364:Tryptophan; D006861:Hydrogen Peroxide; D010544:Peroxidases