中文摘要：

倍半萜合酶家族催化单一底物法尼基焦磷酸形成近300多种链式、单环、双环和三环倍半萜烯、醇,进一步的加工修饰产生种类更加繁多的倍半萜衍生物。详细了解倍半萜合酶产物特异性性决定机制将会为倍半萜合酶的理性设计,定向生成新型化合物打下基础。本研究利用定点突变技术,对紫穗槐二烯合酶RxR基序及相关的D300位点进行了点突变,发现保守基序中R262K单点突变后其酶促反应主产物为（3R）-（E）-nerolidol,而R262L突变使酶失去活性,R264K突变则对产物比例无影响,显示保守基序中第一个精氨酸在活性中心疏水环境的维持中非常关键。D300突变结果显示此氨基酸对酶的活性维持非常必要,结合R262突变结果,推测R262和D300间的非键相互作用对酶活性的维持起重要作用。由于RxR基序在倍半萜合酶家族中非常保守,因此其作用是否具有普遍性值得进一步验证。

英文摘要：

Sesquiterpene synthases catalyze linear precursor farnesyl diphosphate into more than 300 kinds of linear ,monocyclic ,dicyclic or tricylic ring sesquiterpenes w hich numbers will largely increase by succedent modifications .Deeply understanding the mechanism of product specificity of sesquiterpene synthase will lay the foundation of enzyme rational designing for new type of compounds production .In this research ,conserved RxR motif and D300 in amorpa4 ,11diene synthase were mutated to investigate the role of them in enzyme product specificity .The first conserved amino acid R262 mutation to lysine resulted in an enzyme mainly produces （3R）（E）nerolidol and mutation to leucine caused enzyme deactivated ,while the same mutation at the second conserved R264 has no influence on product specificity .These＆amp;nbsp;findings suggest that R262 play a critical role in the reaction center hydrophobic circumstance maintaining .Together with the finding that mutation at D300 causes enzyme deactivated ,we can infer that the nonbond interaction between R262 and D300 may be essential for the enzyme activity .As RXR motif is very conservative in sesquiterpene synthases ,these findings worth to be tested in other sesquiterpene synthases .