Purification and characterization of beta-glucosidase from Weissella cibaria 37

A gene encoding beta-glucosidase was cloned from Weissella cibaria 37, an isolate from human feces. Sequence analysis showed that the gene could encode a protein of 415 amino acids in length, and the translated amino acid sequence showed homology (34-31%) with glycosyl hydrolase family 1 beta-glucosidases. The gene was overexpressed in E. coli BL21(DE3) using pET26b(+) and a 50 kDa protein was overproduced, which matched well with the calculated size of the enzyme, 49,950.87 Da. Recombinant beta-glucosidase was purified by using a his-tag affinity column. The purified beta-glucosidase had an optimum pH and a temperature of 5.5 and 45oC, respectively. Among the metal ions (5mM concentration), Ca2+ slightly increased the activity (108.2%) whereas Cu2+ (46.1%) and Zn2+ (56.7%) reduced the activity. Among the enzyme inhibitors (1 mM concentration), SDS was the strongest inhibitor (16.9%), followed by pepstatin A (45.2%). The Km and Vmax values of purified enzyme were 4.04 mM and 0.92 micromol/min, respectively, when assayed using pNPG (p-nitrophenyl-beta- D-glucopyranoside) as the substrate. The enzyme liberated reducing sugars from carboxymethyl cellulose (CMC).