Fungal polysaccharide monooxygenases: new players in the decomposition of cellulose

Abstract

Traditionally, the models of fungal cellulose hydrolysis have included the actions of endo- and exo-cleaving hydrolytic enzymes, with some involvement of nonspecific cellulose hydrolysis by radical-based oxidative reactions. Only recently, the GH61 glycosyl hydrolases have been demonstrated to be copper-containing enzymes – polysaccharide monooxygenases (PMOs) – internally cleaving cellulose molecules in an oxidative way in synergy with cellobiose dehydrogenase and other cellulolytic enzymes. PMOs can be found in most genomes of ascomycetous and basidiomycetous fungi, including plant pathogens, litter decomposers, white-rot and brown-rot fungi and mycorrhizal fungi. Although their real importance in lignocellulose decomposition is still unknown, their high expression level in the presence of lignocelluloses and substantial synergistic enhancement of cellulose hydrolysis in cooperation with other cellulolytic enzymes seems to indicate their active involvement in cellulose hydrolysis. In a recent report, polysaccharide monooxygenase genes have been reported from litter metatranscriptomes, and their involvement in litter decomposition thus seems likely.