A novel thermophilic β-glucosidase from Caldicellulosiruptor bescii: Characterization and its synergistic catalysis with other cellulases

Bacterial β-glucosidase (BGL), as a major component of the cellulase system, is a rate limiting factor during enzymatic hydrolysis of cellulose. In an effort to obtain thermostable BGLs desirable for application in the conversion of cellulose to glucose, we report a novel recombinant BGL from the thermophile Caldicellulosiruptor bescii (CbBgl1A). CbBgl1A could cleave a range of cellooligosaccharides and aryl-β-glycosides and showed a substrate preference for 4-nitrophenyl β-d-glucopyranoside (pNPGlc) with a kcat/Km value of 84.0 s−1 mM−1. The difference in catalysis efficiency for cellobiose with pNPGlc was mainly caused by the weak binding ability as analyzed by kinetic assay and molecular modeling. The enzyme could tolerate a high concentration of glucose with a Ki value of 113.8 mM. CbBgl1A synergistically works with several endo- or exoglucanases. The highest synergy value of 2.6 was obtained for the hydrolysis of regenerated amorphous cellulose using a combination of cellobiohydrolase CbCbh48A from C. bescii and CbBgl1A at a molar ratio of 1:5, where the complete conversion of oligosaccharides to glucose was obtained in 2 h.