title: Tryptophan-based radical in the catalytic mechanism of versatile peroxidase from Bjerkandera adusta.
abstract: Versatile peroxidase (VP) from Bjerkandera adusta is a structural hybrid between lignin (LiP) and manganese (MnP) peroxidase. This hybrid combines the catalytic properties of the two above peroxidases, being able to oxidize typical LiP and MnP substrates. The catalytic mechanism is that of classical peroxidases, where the substrate oxidation is carried out by a two-electron multistep reaction at the expense of hydrogen peroxide. Elucidation of the structures of intermediates in this process is crucial for understanding the mechanism of substrate oxidation. In this work, the reaction of H(2)O(2) with the enzyme in the absence of substrate has been investigated with electron paramagnetic resonance (EPR) spectroscopy. The results reveal an EPR signal with partially resolved hyperfine structure typical of an organic radical. The yield of this radical is approximately 30%. Progressive microwave power saturation measurements indicate that the radical is weakly coupled to a paramagnetic metal ion, suggesting an amino acid radical in moderate distance from the ferryl heme. A tryptophan radical was identified as a protein-based radical formed during the catalytic mechanism of VP from Bjerkandera adusta through X-band and high-field EPR measurements at 94 GHz, aided by computer simulations for both frequency bands. A close analysis of the theoretical model of the VP from Bjerkandera sp. shows the presence of a tryptophan residue near to the heme prosthetic group, which is solvent-exposed as in the case of LiP and other VPs. The catalytic role of this residue in a long-range electron-transfer pathway is discussed.
authors.affiliation: Department of Chemistry, University of Siena, via Aldo Moro, 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: Stefania
authors.initials: S
authors.lastname: Giansanti
authors.forename: Christian
authors.initials: C
authors.lastname: Teutloff
authors.forename: Jorge
authors.initials: J
authors.lastname: Verdin
authors.forename: Brenda
authors.initials: B
authors.lastname: Valderrama
authors.forename: Friedhelm
authors.initials: F
authors.lastname: Lendzian
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Lubitz
authors.forename: Rafael
authors.initials: R
authors.lastname: Vazquez-Duhalt
authors.forename: Riccardo
authors.initials: R
authors.lastname: Basosi
mesh_terms: D001487:Basidiomycota / Q000201:enzymology*; D002384:Catalysis; D020134:Catalytic Domain; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D005609:Free Radicals / Q000737:chemistry; D008958:Models, Molecular; D010544:Peroxidases / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D014364:Tryptophan / Q000737:chemistry*
chemical_list: D005609:Free Radicals; D014364:Tryptophan; D010544:Peroxidases; C042858:lignin peroxidase; C051129:manganese peroxidase