Sources, properties, and modification of lignocellulolytic enzymes for biomass degradation

Discussion on lignocellulolytic enzymes in this chapter is mainly concerned with enzymes produced by filamentous fungi, which display a broad array of hydrolytic enzymes including cellulases, hemicellulases, and a suite of oxidative enzymes serving diverse functions in lignocellulose degradation. The carbohydrate-active enzymes (CAZymes) are classified into families of Glycoside Hydrolases (GHs), Glycosyl Transferases (GTs), Polysaccharide Lyases (PLs), Carbohydrate Esterases (CEs), and Auxiliary Activities (AAs) based on similarities in their amino-acid sequence. Some of their key properties, genetic modification, and production strategies are discussed here and elsewhere in the book. Among the challenges in working toward economically sustainable enzymatic hydrolysis of lignocellulose for cost-effective production of biofuels and other products is lowering the price of the enzymes and reducing the enzyme load required for hydrolysis. The latter is currently being addressed, for example, by attempts to improve the thermotolerance and catalytic activity of the key enzymes such as CBHI (Cel7A). A more recent line of research is exploring novel enzymes and nonhydrolytic proteins assisting in biomass degradation and designing substrate-tailored enzyme mixtures exposed by secretome displays and genome sequence analysis.