GH11家族木聚糖酶底物选择性分子机制探究及半理性设计提高木聚糖酶对水不溶底物的活性

木聚糖酶可将富含木聚糖的农业生物质转化为高附加值的益生元低聚木糖，产生巨大的经济和环境效益。大部分木聚糖酶对水不溶木聚糖（WIX）催化活性较低，木质纤维素需要经过额外的预处理以增加木聚糖的溶解度，提高酶对底物的可及性。但是，复杂的预处理会增加生产成本并带来环境污染。挖掘对WIX具有高选择性和高活性的酶资源，是解决这一问题实现木聚糖绿色转化的基础。然而，木糖酶对WIX高选择性的结构基础并不清楚。本课题对前期获得的底物选择性完全不同的高活性木聚糖酶Xyn11A和Xyn11B比较研究，解析Xyn11A 与WIX的作用过程，探究Xyn11A和Xyn11B对WIX选择差异性的结构基础，揭示GH11家族木聚糖酶对WIX底物选择性分子机制。并指导Xyn11B定向改造，保留其高酶活并提高其对WIX选择性。项目实施可为开发高WIX选择性高活性木聚糖酶资源提供理论支撑和技术借鉴，为实现木聚糖绿色转化奠定基础。

Xylanase can hydrolyses the xylan-rich agricultural biomass to release valua-added xylooligosaccharides with prebiotic properties that yield economic and environmental advantages. Most known xylanases displayed low activity toward water-insoluble xylan (WIX), so that lignocellulose needs to be pretreated to increase the solubility of xylan and improve enzyme accessibility and digestibility to the substrate. Undoubtedly, complex pretreatment leads to great increment of xylan biotransformation and severe environmental pollution. Therefore, mining novel xylanases with high selectivity and high activity toward WIX is promising strategy for solving this problem and realizing the green conversion of xylan. However, the structural basis for the high selectivity toward WIX of xylanase remains as to be investigated, as well as the resources of xylanase with high activity and high WIX selectivity are still in lacked. In this project, two xylanases Xyn11A and Xyn11B, with different substrate selectivity, would be compared and analyzed for the interaction with WIX, and the structural basis for the high selectivity towards WIX would be explored and the mechanism of substrate selectivity of GH11 family xylanase would be revealed. Guided by the mechanism of substrate selectivity, the catalysis improvement of Xyn11B toward insoluble xylan could be designed by semi-rational approach. And we could obtain a mutant of Xyn11B with high activity and high substrate selectivity toward WIX. The implementation of the project can provide strategy for developing xylanase resources with high WIX selectivity and high activity and realizing green conversion of xylan based on theory and technology.