白蚁及其共生菌来源的4种木质纤维素酶的共表达

Co-expression of lignocellulase from termite and their endosymbionts

摘要:

天然的木质纤维素材料含有纤维素、半纤维素和木质素等成分。降解天然木质纤维素底物时，需要木质纤维素酶共同作用。近年在木质纤维素酶的相互协同作用方面的研究引起人们的关注，成为一个新的研究热点，文中使用两个不同的共表达载体pETDuet-1和pRSFDuet-1，在大肠杆菌中共表达了白蚁及其肠道微生物来源的β-葡萄糖苷酶、内切β-1,4-葡聚糖酶、漆酶和木聚糖酶这4种木质纤维素酶，经过SDS-PAGE分析得到了与理论值一致的蛋白条带，同时经过酶活验证，这4种蛋白都具有酶活性。以磷酸处理的微晶纤维素 (PASC) 为底物，测定了共表达酶粗酶液与单独表达酶混合液的协同作用因子，从还原糖的产量上经计算共表达的粗酶液比单独表达酶的混合液对PASC的降解协同作用提高44%；以滤纸和磷酸处理的玉米芯为底物，测定降解协同作用，分别提高了34%和20%。结果表明，共表达酶的降解效率要高于混合的单组分酶液降解效率的总和。

Abstract:

Natural lignocellulosic materials contain cellulose, hemicellulose, and lignin. Cellulose hydrolysis to glucose requires a series of lignocellulases. Recently, the research on the synergistic effect of lignocellulases has become a new research focus. Here, four lignocellulase genes encoding β-glucosidase, endo-1,4-β-glucanase, xylanase and laccase from termite and their endosymbionts were cloned into pETDuet-1 and pRSFDuet-1 and expressed in Escherichia coli. After SDS-PAGE analysis, the corresponding protein bands consistent with the theoretical values were observed and all the proteins showed enzyme activities. We used phosphoric acid swollen cellulose (PASC) as substrate to measure the synergistic effect of crude extracts of co-expressing enzymes and the mixture of single enzyme. The co-expressed enzymes increased the degradation efficiency of PASC by 44% compared with the single enzyme mixture; while the degradation rate increased by 34% and 20%, respectively when using filter paper and corn cob pretreated with phosphoric acid as substrates. The degradation efficiency of the co-expressed enzymes was higher than the total efficiency of the single enzyme mixture.