Monday, April 29, 2013
Exhibit Hall
Endoglucanase is an important component in the cellulase enzymatic system. The great efforts have been made to discover novel endoglucanases with high activity and outstanding stability, especially from extremophiles. In this study, a novel β-1,4- endoglucanase was cloned from Dictyoglomus thermophilum, which was the first endoglucanase reported from this organism and designated as Cel5H for being a member of glycoside hydrolase family 5. The purified endoglucanase from recombinant Escherichia coli showed highly hydrolytic activities on carboxylmethyl cellulose with a broad optimal temperature of 50-85°C and the optimum pH of 5.0. Furthermore, this enzyme was thermostable with a half-life of 336 h at 75°C and lost less than 20% of enzymatic activity after 135 days incubation at 50°C. To enhance the performance of the thermophilic endoglucanase, chimeric enzymes including Cel5H and syncretic cellulose binding module (CBM) were construted. The CBMs from different sources at different locations (N- or C- terminus of the catalytic domain) were investigated. The results showed that all the CBMs were effective. In addition, Cel5H was highly tolerant to high salt concentration although the organism was not salt-tolerant bacterium. To explore the mechanism of salt-tolerance, three-dimensional structure of Cel5H was developed by homology modeling methods and surface electrostatic analysis was performed.It is hypothesized to be good candidates for lionic liquid resistant cellulases in the pretreatment due to its ability to accommodate high salinity environments. This endoglucanase appears to have tremendous commercial potential.