Cellulose-degrading enzymes: key players in biorefinery development

Saccharification recalcitrance significantly limits the conversion of lignocellulosic biomass to valuable end products. The intricate arrangement between cell wall matrix polysaccharides, proteins, and lignin makes the cell wall structure a challenging substrate for carbohydrase and ligninase accessibility. Cellulose valorization from biomass or via conversion into valuable bioproducts, including bioethanol, is a strategic pathway for the economic viability and full implementation of lignocellulose biorefineries. The enzymatic hydrolysis of cellulose into sugar monomers has emerged as the most efficient biomass conversion technology. Synergistic degradation of cellulosic biomass components is achieved using a consortium of enzymes, including cellulases, lytic polysaccharide monooxygenases, and cellobiose dehydrogenases combined with proteins, such as swollenins and expansins. The immobilization of cellulose-degrading enzymes with an appropriate matrix requires careful examination to achieve successful cellulose breakdown. Genetic modification of filamentous fungi provides an avenue to generate strains with high enzyme production. This review focuses on the mechanisms of action of cellulose-degrading enzymes and their contribution to improving bioethanol production from plant biomass and discusses technologies and strategies aimed at reducing costs for lignocellulosic biorefineries.