The construction of Thermotoga maritima endoglucanase Cel12B fused with CBD and the characterization of chimeric enzyme
海栖热袍菌内切葡聚糖酶Cel12B与木聚糖酶XynA CBD结构域融合基因的构建、表达及融合酶性质分析

Thermotoga maritima is strictly anaerobic and extremely thermophilic bacteria. The endoglucanase found in T. maritima showed extremely high thermostability and considerable potential in industrial application. Endoglucanase (Tm) Cel12B is extracellular enzyme. Tm Cel12B did not contain a cellulose-binding domain (CBD)and lacked activity on crystalline cellulose. Tm XynA is composed of catalytic domain (CD) and cellulose-binding domain (CBD). As such, the gene of CBD from Tm XynA was fused at the carboxyl-terminus of Tm Cel12B and recombinant plasmid pET-20b- Cel 12B- CBD was obtained. The recombinant plasmid pET-20b- Cel 12 B- CBD was transformed to E. coli JM109 (DE3), induced by IPTG. The properties of chimeric enzyme were determined. The chimeric enzyme displayed pH activity and stability profiles similar to those of parental enzyme with optimal pH 5.8. The optimal activity of the chimera was observed at 100 degrees C and the enzyme kept 87% of original enzyme activity after incubated at 90 degrees C for 2h. A notable feature on substrate specificity is that the chimeric enzyme has the capacity to hydrolases crystalline cellulose.