中文摘要：

为提高米曲霉11家族中温木聚糖酶AoXyn11A的热稳定性,将AoXyn11A与源于Thermomyces lanuginosus的耐热木聚糖酶XynA进行三维结构比对分析,发现XynA的α-螺旋与β9-折叠之间存在一个二硫键;基于分子动力学模拟预测结果,利用定点突变技术在AoXyn11A的相应位置引入二硫键（Cys^108-Cys^152）,获得突变酶AoXyn11AT;分别将AoXyn11A及其突变酶基因在大肠杆菌BL21（DE3）中表达,经纯化,获得重组AoXyn11A和AoXyn11AT,并分析比较温度对其酶活性的影响。结果显示,重组AoXyn11AT的最适温度为60℃,比重组AoXyn11A提高了5℃;其在50℃下的半衰期t1/2^50为71 min,较重组AoXyn11A（t1/2^50=25 min）提高了近2倍。研究表明二硫键对提高AoXyn11A的热稳定性有重要作用。

英文摘要：

To improve the thermostability of the family 11 xylanase AoXyn11 A from Aspergillus oryzae,homology alignment and analysis of the three dimensional structures between thermostable xylanase Xyn A from Thermomyces lanuginosus and Ao Xyn11 A were carried out. Resultantly,a disulfide bridge was located between the α-helix and β9 sheet of Xyn A while none in AoXyn11 A.Based on the prediction by molecular dynamics simulation,a disulfide bridge（Cys^108-Cys^152） was introduced into the corresponding region（α-helix region） of AoXyn11 A by site-directed mutagenesis. The mutant xylanase,AoXyn11 AT,was obtained. Then,the AoXyn11A- and AoXyn11AT-encoding genes were separately expressed in Escherichia coli BL21（DE3）. After purification,the effects of temperature on xylanase activity of the recombinant AoXyn11 A and AoXyn11 ATwere analyzed and compared. The temperature optimum（Topt） of the recombinant AoXyn11 ATwas 60 ℃,which was 5 ℃ higher than that of the recombinant AoXyn11 A. The half-life of the recombinant Ao Xyn11 ATat 50 ℃（t1/2^50） was 71 min,which was about 3-fold than that（25min） of the recombinant Ao Xyn11 A. This study demonstrated that the disulfide bridge played an important role in thermostability improvement of the xylanase Ao Xyn11 A.