改造嗜熱菌株之纖維素水解酶與甘露糖水解酶並研究其酵素特性以及分解纖維素產生生質能之應用

Abstract

Clostridium thermocellum endoglucanase CelT hydrolyzes internal β-1,4-glucosidic linkages along the cellulose chains to release shorter fragments. The CelT consists of a family-9 catalytic domain of the glycoside hydrolases, and a dockerin domain responsible for cellulosome assembly, but lacks a cellulose-binding domain, which is often found with family 9 catalytic domains. This study is focused on improving cellulolytic efficiency of CelT. The family-3 cellulose binding domain (CBD) from C. thermocellum cel9I was fused to the catalytic domain of CelT to generate CelT-CBD fusion protein. CelT-CBD is more active toward insoluble celluloses than the CelT (devoid of the region encoding the dockerin domain). The result indicates that the construction of a fusion protein using CBD from another thermophilic endoglucanase represents a possible strategy for obtaining higher activity toward insoluble cellulose substrates. In the case of the CelT-CBD catalyzed hydrolysis of phosphoric acid-swollen cellulose (PASC), the soluble sugars were released at a 4-fold higher rate to compared with wild type CelT. Due to the heterogeneity in the composition and the structure of the plant cell wall, a wide range of enzymes is required for the biodegradation of these polysaccharides. Previous studies also showed that cellulosomal enzymes work synergistically for efficient lignocelluloses degradation. To improve efficiently of plant cell wall degradation, the synergistic interactions of endoglucanse (CelT△doc) and β-mannanase (ManCthe0032△doc) were determined on the degradation of rice straw biomass. The results showed an increased rate of reducing sugar production by the addition of CelT△doc and ManCthe0032△doc when comparing to the sum of the individual activities of the corresponding enzymes.