Characteristics of chimeric enzymes constructed between Thermotoga maritima and Agrobacterium tumefaciens β-glucosidases: Role of C-terminal domain in catalytic activity

The importance of C-terminal domain of β-glucosidase (family 3 glycosidase) from Thermotoga maritima, a hyper-thermophilic bacterium was investigated by gene shuffling. The amino acid sequences of β-glucosidases from T. maritima and A. tumefaciens share high degree of homology (approximately 40%). However, despite such a high homology, both enzymes exhibited quite distinct characteristics in terms of their pH and temperature profile and substrate specificities. To investigate the functional role of the C-terminal domains of T. maritima and A. tumefaciens β-glucosidases, three chimeric genes were constructed by shuffling at three selected regions. Out of the three chimeric enzymes, only two (Tm533/626At and Tm630/727At) were catalytically active. Parental and the chimeric enzymes were subsequently characterized for the substrate specificities and their response towards pH and temperature. Our results revealed that C-terminal domain was catalytically important. The study clearly establishes the significance of gene shuffling in probing the structure and function relationship in hyper-thermophilic bacterium and evolving enzymes with altered features.