嗜热子囊菌JCM12803来源的双功能木聚糖/纤维素酶

A novel bifunctional xylanase/cellulase TcXyn10A from Thermoascus crustaceus JCM12803

摘要:

纤维素和木聚糖的充分利用对于生物燃料的生产是非常重要的。文中利用PCR的方法从嗜热子囊菌Thermoascus crustaceus JCM12803中克隆到一个新颖的双功能木聚糖/纤维素酶基因Tcxyn10a，并将其在毕赤酵母Pichia pastoris GS115中实现高效异源表达。经过蛋白纯化和酶学性质研究分析，TcXyn10A的最适pH值和最适温度分别为5.0和65?70 ℃，能够在酸性至碱性 (pH 3.0?11.0) 条件下和60 ℃下保持稳定；对榉木木聚糖、小麦阿拉伯木聚糖、羧甲基纤维素钠和地衣多糖均有降解活性，比活分别为(1 480±26) U/mg、(2 055±28) U/mg、(7.4±0.2) U/mg和 (10.9±0.4) U/mg；同源建模结构以及分子对接试验表明，双功能酶TcXyn10A只含有单一催化结构域，且木聚糖底物与纤维素底物共用一条催化通道。文中为探索双功能酶结构与其功能的关系提供了很好的素材。

Abstract:

Efficient utilization of cellulose and xylan is of importance in the bioethanol industry. In this study, a novel bifunctional xylanase/cellulase gene, Tcxyn10a, was cloned from Thermoascus crustaceus JCM12803, and the gene product was successfully overexpressed in Pichia pastoris GS115. The recombinant protein was then purified and characterized. The pH and temperature optima of TcXyn10A were determined to be 5.0 and 65?70 °C, respectively. The enzyme retained stable under acid to alkaline conditions (pH 3.0?11.0) or after 1-h treatment at 60 °C. The specific activities of TcXyn10A towards beechwood xylan, wheat arabinoxylan, sodium carboxymethyl cellulose and lichenan were (1 480±26) U/mg, (2 055±28) U/mg, (7.4±0.2) U/mg and (10.9±0.4) U/mg, respectively. Homologous modeling and molecular docking analyses indicated that the bifunctional TcXyn10A has a single catalytic domain, in which the substrate xylan and cellulose shared the same binding cleft. This study provides a valuable material for the study of structure and function relationship of bifunctional enzymes.