环糊精葡葡萄糖基转移酶热稳定性的研究

Thermostability study of cyclodextrin glycosyltransferase

环糊精葡萄糖基转移酶(CGTase;EC 2.4.1.19)是一种重要的环糊精生产工业用酶,该转移酶能进行环化、偶合、歧化、水解4种反应。环糊精广泛的用于食品、医药、化妆品、农业和化学工业等生产领域,为了提高环糊精的产量,需要CGTase具有更高的热稳定性。合理的设计耐热蛋白已经成为研究热点。在本文中,首次使用分子动力学模拟研究CGTase热稳定性,以补充实验上不易获得的原子能级和时间相关的信息。使用同源建模方法构建环糊精葡糖基转移酶及其突变体的三维结构,研究氨基酸的突变对CGTase酶耐热性的影响,用CHARMM能量计算CGTase及其突变体的能量与酶蛋白热稳定性之间的关系。证明:氨基酸残基经过突变,突变型比野生型含带电残基更多。相应的,在蛋白天然结构中突变型CGTase中,盐桥数量增加了10%。这些电荷之间、非极性残基之间的非共价键作用力的增强,提高了突变体的刚性,降低了突变体蛋白质分子的总能量,最后增加突变体蛋白质的耐热性。

Cyclodextrin glycosyltransferase（CGTase;EC 2.4.1.19） is an important industrial enzyme in the production of cyclodcxtrins,the enzyme possesses cyclization,coupling,disproportionation and hydrolytic activities.CDs have been widely applied in food,pharmaceutical,cosmetic,agricultural and chemical industries.In order to improve CD production,more thermostable and thermoactive CGTases are desirable.Rational designing of thermostable variants of mesophilic proteins is well motivated.In this work,molecular dynamics simulations were performed to study thermal stabilization of CGTase protein.MD provides atomic level and time-dependent information which are not easily obtained by experiments.The 3D structure of CGTase and its mutant were modeled by homology modeling.The influence of amino acids mutation on protein thermostability and the relationship between the energy and the thermostability of the CGTase and its mutant were studied by CHARMM energy.The results show that the mutant contains more charged residues than that of wild-type by mutation of amino acids,accordingly,the natural structure of the mutant CGTase has more salt-bridges.The increase of the non-covalent bond force between charges and residues and decrease of the total energy and flexibility of the protein resulted in the increase of the thermostability.