Identification and Characterization of Two Endogenous β-Glucosidases from the Termite Coptotermes formosanus

Coptotermes formosanus is a well-known wood-feeding termite that can degrade lignocellulose polysaccharides efficiently with its unique multi-enzyme catalysis system. β-glucosidase (BG) is one of the important cellulases in its enzyme system. However, there may present multiple endogenous BGs in termite digestive system for various properties and functions. This study aims to characterize two BG homologs and reveal their potential coordinative effect. In this study, two endogenous BG homologs (CfGlu1B and CfGlu1C) from C. formosanus showed different substrate specificity. CfGlu1B favors cellobiose while CfGlu1C favors sucrose. Besides, CfGlu1C exhibited higher alkali resistance than CfGlu1B. Kinetic analysis revealed that CfGlu1B enzyme's activity toward p-NP-β-D-glucopyranoside (p-NPG) was higher than that of CfGlu1C, and the difference mainly attributes to the turnover number (K cat). In addition, the activity assay showed significant synergistic action of CfGlu1B and CfGlu1C in degrading D-lactosum. For effect of metals, Cu(2+) inhibited both enzymes and Ca(2+) increased the activity of CfGlu1C but not CfGlu1B. Site-directed mutagenesis analysis indicated that both enzymes lost activities when residues E190 of CfGlu1B and E168 of CfGlu1C were mutated to alanine, respectively, which were essential active centers of the GHF1 enzymes. Moreover, mutation H252N increased the activity of enzyme CfGlu1C by 2.1-fold. This study implies interesting possibilities for better practical biotechnological use in green energy production.