β-Glucosidases

beta-Glucosidases (3.2.1.21) are found in all domains of living organisms, where they play essential roles in the removal of nonreducing terminal glucosyl residues from saccharides and glycosides. beta-Glucosidases function in glycolipid and exogenous glycoside metabolism in animals, defense, cell wall lignification, cell wall beta-glucan turnover, phytohormone activation, and release of aromatic compounds in plants, and biomass conversion in microorganisms. These functions lead to many agricultural and industrial applications. beta-Glucosidases have been classified into glycoside hydrolase (GH) families GH1, GH3, GH5, GH9, and GH30, based on their amino acid sequences, while other beta-glucosidases remain to be classified. The GH1, GH5, and GH30 beta-glucosidases fall in GH Clan A, which consists of proteins with (beta/alpha)(8)-barrel structures. In contrast, the active site of GH3 enzymes comprises two domains, while GH9 enzymes have (alpha/alpha)(6) barrel structures. The mechanism by which GH1 enzymes recognize and hydrolyze substrates with different specificities remains an area of intense study.