Phenol oxidation by DyP-type peroxidases in comparison to fungal and plant peroxidases

Over the last years, novel peroxidases secreted by lignocellulose-degrading agaricomycetes have been discovered. Among them, the so-called DyP-type peroxidases (DyPs) that are secreted under conditions close to nature (i.e. in wood cultures) are of particular interest, since they are able to oxidize diverse substrates including veratryl alcohol, non-phenolic lignin model dimers as well as recalcitrant phenols and dyes. In spite of their unique protein structure and their catalytic versatility, the estimation of the redox potential of this new peroxidase group is still pending. To solve this problem, we used a catalytic approach developed by Ayala et al., 2007 [21], which is based on the Marcus equation and the determination of the redox thermodynamics between heme-peroxidase compound II and the resting state enzyme. Five fungal DyPs (among them four wild-type enzymes and one recombinant protein) were tested regarding phenol oxidation in comparison to other well-studied plant and fungal peroxidases (soybean peroxidase, SBP, Coprinopsis cinerea peroxidase, CiP, lignin peroxidase of Phanerochaete chrysosporium, LiP). DyP-type peroxidases have a high affinity for phenols and can oxidize even recalcitrant representatives such as p-nitrophenol. Based on this “phenol oxidation method”, their redox potential was estimated to range between 1.10 ± 0.02 and 1.20 ± 0.1 V, which is between the values calculated for high-redox potential LiP (1.26 ± 0.17 V) and low-redox potential, phenol-oxidizing plant (0.93 ± 0.04 V for SBP) and fungal (1.06 ± 0.07 V for CiP) peroxidases.