Molecular characterization of a novel peroxidase isolated from the ligninolytic fungus Pleurotus eryngii

A haem peroxidase different from other microbial, plant and animal peroxida ses is described. The enzyme is secreted as two isoforms by dikaryotic Pleu rotus eryngii in peptone-containing liquid medium. The corresponding gene, which presents 15 introns and encodes a 361-amino-acid protein with a 30-am ino-acid signal peptide, was isolated as two alleles corresponding to the t wo isoforms. The alleles differ in three amino acid residues and in a seven nucleotide deletion affecting a single metal response element in the promo ter. When compared with Phanerochaete chrysosporium peroxidases, the new en zyme appears closer to lignin peroxidase (LIP) than to Mn-dependent peroxid ase (MnP) isoenzymes (58-60% and 55% identity respectively). The molecular model built using crystal structures of three fungal peroxidases as templat es, also showed high structural affinity with LIP (C-alpha-distance 1.2 Ang strom). However, this peroxidase includes a Mn2+ binding site formed by thr ee acidic residues (E36, E40 and D175) near the haem internal propionate, w hich accounts for the ability to oxidize Mn2+. Its capability to oxidize ar omatic substrates could involve interactions with aromatic residues at the edge of the haem channel. Another possibility its long-range electron trans fer, e.g. from W164, which occupies the same position of LIP W171 recently reported as involved in the catalytic cycle of LIP.