Improved Lignocellulose Degradation Efficiency by Fusion of β-Glucosidase, Exoglucanase, and Carbohydrate-Binding Module from Caldicellulosiruptor saccharolyticus

Jilin Xia, Yu Yu, Huimin Chen, Jia Zhou, Zhongbiao Tan, Shuai He, Xiaoyan Zhu, Hao Shi, Pei Liu, Muhammad Bilal, Xiangqian Li

Abstract


Bifunctional cellulases with β-glucosidase (Bgl1), exoglucanase (Exo5), and carbohydrate-binding modules (CBMs) from Caldicellulosiruptor saccharolyticus were fused to yield several recombinant plasmids, Bgl1-CBM-Exo5, Bgl1-2CBM-Exo5, and Bgl1-3CBM-Exo5. The fused enzymes possessed both β-glucosidase and exoglucanase activities and were used to improve the degradation efficiency of lignocellulosic biomass. The optimal temperature of Bgl1-3CBM-Exo5 was 70 °C, which was the same as Bgl1, and the optimal temperature of the other two enzymes was 80 °C, which was the same as Exo5. The optimal pH of fused enzymes was 4 to 5, the same as Exo5, but the optimal pH of Bgl1 was 5.5. Compared with Bgl1-CBM-Exo5 and Bgl1-2CBM-Exo5, the hydrolysis efficiency of Bgl1-3CBM-Exo5 on sodium carboxymethyl cellulose (CMC-Na) was increased by 67% and 50%, respectively. The activities of these enzymes on CMC-Na were increased by 128 to 192% when 10 mM MnCl2 was added. Filter paper, microcrystalline cellulose (MCC), steam-pretreated rice straw, rice straw, and wheat straw were efficiently degraded by these fused enzymes. Specific activities of the fusion enzymes on MCC reached 34.4 to 76.4 U/μmol. The results indicated that bifunctional cellulases fused with CBMs were functional on cellulosic biomass, and CBMs contributed to further deconstruction of MCC and other natural substrates.

Keywords


β-glucosidase; Exoglucanase; Fusion enzymes; CBM; Caldicellulosiruptor saccharolyticus

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