First Dye-Decolorizing Peroxidase from an Ascomycetous Fungus Secreted by Xylaria grammica

Background: Fungal DyP-type peroxidases have so far been described exclusively for basidiomycetes. Moreover, peroxidases from ascomycetes that oxidize Mn(2+) ions are yet not known. Methods: We describe here the physicochemical, biocatalytic, and molecular characterization of a DyP-type peroxidase (DyP, EC 1.11.1.19) from an ascomycetous fungus. Results: The enzyme oxidizes classic peroxidase substrates such as 2,6-DMP but also veratryl alcohol and notably Mn(2+) to Mn(3+) ions, suggesting a physiological function of this DyP in lignin modification. The K(M) value (49 µM) indicates that Mn(2+) ions bind with high affinity to the XgrDyP protein but their subsequent oxidation into reactive Mn(3+) proceeds with moderate efficiency compared to MnPs and VPs. Mn(2+) oxidation was most effective at an acidic pH (between 4.0 and 5.0) and a hypothetical surface exposed an Mn(2+) binding site comprising three acidic amino acids (two aspartates and one glutamate) could be localized within the hypothetical XgrDyP structure. The oxidation of Mn(2+) ions is seemingly supported by four aromatic amino acids that mediate an electron transfer from the surface to the heme center. Conclusions: Our findings shed new light on the possible involvement of DyP-type peroxidases in lignocellulose degradation, especially by fungi that lack prototypical ligninolytic class II peroxidases.