First Dye-Decolorizing Peroxidase from an Ascomycetous Fungus Secreted by <i>Xylaria grammica</i>

• Main Authors: Virginia Kimani, René Ullrich, Enrico Büttner, Robert Herzog, Harald Kellner, Nico Jehmlich, Martin Hofrichter, Christiane Liers
• Format: Article
• Language: English
• Published: MDPI AG 2021-09-01
• Series: Biomolecules
• Subjects: dye-decolorizing peroxidase; <i>Xylaria grammica</i>; ascomycete; Mn²⁺ oxidation; Mn²⁺ binding site
• Online Access: https://www.mdpi.com/2218-273X/11/9/1391
• ISSN: 2218-273X

Background: Fungal DyP-type peroxidases have so far been described exclusively for basidiomycetes. Moreover, peroxidases from ascomycetes that oxidize Mn²⁺ 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 Mn²⁺ to Mn³⁺ ions, suggesting a physiological function of this DyP in lignin modification. The K_M value (49 µM) indicates that Mn²⁺ ions bind with high affinity to the <i>Xgr</i>DyP protein but their subsequent oxidation into reactive Mn³⁺ proceeds with moderate efficiency compared to MnPs and VPs. Mn²⁺ oxidation was most effective at an acidic pH (between 4.0 and 5.0) and a hypothetical surface exposed an Mn²⁺ binding site comprising three acidic amino acids (two aspartates and one glutamate) could be localized within the hypothetical <i>Xgr</i>DyP structure. The oxidation of Mn²⁺ 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.