Characterization of a novel laccase from Melanocarpus albomyces

Laccases are multi-copper containing enzymes, which catalyze the oxidation of a variety of organic and inorganic substrates coupled to the reduction of molecular oxygen to water with the one-electron oxidation mechanism. Laccase-based mediated pulp bleaching systems have been developed and tested in pilot-scale. The ability of laccases to oxidize lignin is currently exploited in activation of fibre surfaces for bonding, grafting or glueing applications. It is essential for many applications to discover laccases, which work at relatively high pHs and elevated temperatures. We report here on a novel laccase from the ascomycete Melanocarpus albomyces with very interesting properties. The enzyme had a pH optimum measured with quaiacol at a neutral pH range and significant activity still at pH 8. The laccase showed very good thermostability, retaining full activity for two hours at 60°C. The gene encoding the M albomyces laccase was isolated and sequenced. The length of the open reading frame of the M. albomyces laccase was 623 amino acid residues. The amino acid sequence had high homology to other ascomycete laccases. Heterologous expression of the M albomyces laccase was carried out in Trichoderma reesei with high yields. The laccase was crystallized with all four coppers present, and the crystal structure was determined at 2.4 A resolution. The M albomyces laccase combined with NHA mediator showed good delignification efficiency on kraft pulp.