Fusion of beta glucosidase (BglA) to endoglucanase (Cel5L), enhanced their activities and thermostability

Abstract

Beta-glucosidase gene (BglA) from Thermotoga maritima was fused to C- terminus of the catalytic domain of Cel5L from Clsotridium thermocellum with a linker sequence between the two domains. Fusion construct Cel5L-BglA was expressed in E. coli. The cellulase and the beta glucosidase activities in the fusion construct increased 2.0 and 1.8 fold, respectively as compared to their activities in free states. The component enzyme activities in the fusion were stable at 80 ^oC for 2 h. The optimum temperatures for endoglucanase and beta glucosidase activities of the fusion construct were found to be 70 and 90 ^oC, respectively under the assay conditions used. Optimum pH for endoglucanase activity was found to be 6.0, while for β-glucosidase activity optimum pH was 5.0. The HPLC analysis of the hydrolysates showed that the bifunctional enzyme Cel5L-BglA can efficiently hydrolyze CMC, producing glucose as the major end product.