Hoi-Shan Kwan, Kin-Sing Wong, Valdeir Arantes and Jack N. Saddler
School of Life Sciences, the Chinese University of Hong Kong, Shatin, Hong Kong
Laccases from basidiomycetes, and their laccase-mediator systems (LMSs), are versatile biocatalysts for “green” applications. We determined the genome sequence of Shiitake mushroom Lentinula edodes and clone and express recombinant laccases in Pichia pastoris. We purified and characterised two allelic recombinant laccases, multi-copper oxidases that catalyse the oxidation of phenolic compounds using molecular oxygen as oxidant. With mediators, substrate specificity of laccases relaxes can oxidize substrates with high redox potential. The laccase Lcc1A and its LMSs were the most efficient in biodegradation of synthetic dyes and polyaromatic hydrocarbons, and could improve the enzymatic saccharification of steam-pretreated softwoods by 37% to 46%. The laccases can be used as “accessory” enzymes, when added to a typical cellulase enzyme mixture, enhanced the hydrolysis of cellulose in pretreated softwoods. We tested the supplementation of the recombinant laccase and mediators to a cellulase cocktail to hydrolyze steam pretreated lignocellulosic substrates. The optimised LMS enhanced the hydrolysis of pretreated softwoods but not agricultural residues or hardwoods. The enzyme-mediator mixtures were further tested to hydrolyze different steam pretreated softwoods (to obtain ≥ 70% hydrolysis). We demonstrated the “green” applications of recombinant L. edodes laccases and provided new enzyme recipes for efficient bioconversion of softwoods.