Heterologous expression and enzymatic characterization of .BETA.-glucosidase from the drywood-eating termite, Neotermes koshunensis

Abstract

A β-glucosidase cDNA from the termite, Neotermes koshunensis, was successfully overexpressed in Escherichia coli, and the product was purified to homogeneity by affinity purification against His-tags. The molecular weight of the recombinant enzyme was 60 kDa. The expressed β-glucosidase preferentially hydrolyzed laminaribiose and cellobiose rather than synthetic substrates such as p-nitrophenolic compounds. The Km value of cellobiose was 3.8 mM and Vmax was 220 U (μmol of glucose/min)/mg. The optimum pH and thermostability were 5.0 and 45°C, respectively. These enzymatic characters are mostly consistent with the partially-purified β-glucosidase from the salivary glands of N. koshunensis. However, the specific activity of the recombinant enzyme was 156.7 U/mg, which is almost 3-folds of that of the partially purified β-glucosidase of N. koshunensis. Owing to the successful expression of the termite β-glucosidase in E. coli, it may provide an opportunity of termite β-glucosidase for further improvement of the enzymatic properties for potential industrial applications with the aid of bioengineering.