Abstract
In this study, a previously cloned β-glucosidase gene, umbgl3B, was heterologously expressed in Escherichia coli, and the biochemical properties of the purified enzyme were characterized. The recombinant enzyme was stable over a wide range of pH values (5.0–9.0) and below 30 °C. It displayed optimum enzymatic activity at pH 6.5 at 40 °C, under condition similar to that in the rabbit cecum, suggesting an active role of the native enzyme in vivo. The recombinant β-glucosidase Umbgl3B showed high activity to aryl β-D-glucosides and low activity to cellooligosaccharides, with a polymerization degree of less than 5. The enzyme had no activity toward long cellooligosaccharides or polysaccharides. The aspartic acid residue, D772, of the wild-type Umbgl3B was predicted as a nucleophile. Mutant D772A was constructed. It showed less than 1/10,000 activity of the wild-type enzyme, but had the same properties, suggesting that residue D772 plays a key role in the enzyme’s activity.
