CONSTRUCTION AND CHARACTERIZATION OF A CHIMERIC BETA-GLUCOSIDASE

The amino acid sequences of beta-glucosidases from Cellvibrio gilvus and Agrobacterium tumefaciens show significant similarity in most of the parts. However, the pH/temperature optima and stabilities of the two enzymes are quite different. C. gilvus beta-glucosidase exhibits an optimum pH of 6.2-6.4 and temperature of 35 degrees C, whereas the corresponding values for A. tumefaciens are 7.2-7.4 and 60 degrees C respectively. To analyse these properties further, a chimeric beta-glucosidase was constructed by replacing a segment from the C-terminal region of C. gilvus beta-glucosidase gene with that of A. tumefaciens. The partially purified chimeric enzyme was characterized with respect to pH/temperature activity and stability and substrate affinity. Our results suggest that C-terminal segment(s) might be important in beta-glucosidase specificity, and shuffling of even a small segment of gene in this region might significantly alter or improve the enzymic properties such as thermal stability.