基于理性设计提高产微球茎菌AG1琼胶酶的热稳定性

Improving Thermal Stability of Microbulbifer sp. AG1 Agarase Based on Rational Design

目的:对产微球茎菌AG1的琼胶酶基因进行理性化设计,获得酶热稳定性高的突变酶。方法:利用PoP鄄MuSiC在线分析工具对AG1的琼胶酶序列进行分析,选择提高酶热稳定性的突变位点,利用重叠延伸PCR技术获得突变体基因,并对突变酶进行诱导表达、纯化及性质鉴定。结果:通过筛选获得琼胶酶热稳定性高的突变体D136N。在60℃下处理1 h,该突变酶保持87%的残余活力,而野生型为19%的残余活力,说明突变体D136N具有较好的热稳定性。酶的三维结构模拟显示,野生型Asp136与Asn255形成两个氢键,与Tyr282形成一个氢键;突变后的Asn136和Asn255形成3个氢键,与Tyr282形成一个氢键,还与Ala134形成了一个氢键,突变酶的136位氨基酸与周围氨基酸形成更多的氢键。结论:通过理性化设计获得产微球茎菌AG1琼胶酶热稳定性高的突变体D136N,对改善酶的性质,扩大琼胶酶的应用范围,以及研究琼胶酶结构与功能关系具有重要意义。

Objective:This study was aimed to improve the thermal stability of agarase from Microbulbifer sp.AG1 by rational design.Methods:According to the analysis of PoPMuSiC online analytical tool,the mutation site where the stability of agarase could be improved was selected.The mutant gene was obtained by means of overlapping extension PCR.After induction,expression and purification,the mutant enzyme was characterized.Results:The mutant D136N with improved thermostability was obtained after screening.After incubation at 60℃for 1 h,the mutant could maintain about 87%of residual activity,while the wild-type agarase could retain 19%of residual activity.The mutant enzyme D136N had a better thermal stability.Three-dimensional modeling showed that Asp136 formed two hydrogen bonds with Asn255 and one hydrogen bond with Tyr282 in the wild-type agarase.In the mutated enzyme,Asn136 formed three hydrogen bonds with Asn255,one hydrogen bond with Tyr282,and one hydrogen bond with Ala134.Therefore,the amino acid site of 136 was able to form more hydrogen bonds with its surrounding amino acid residues in the mutant of D136N.Conclusion:The mutant D136N with improved thermostability was obtained by the rational design.It is important to improve the enzymatic properties,to expand the application of agarase,and to study the relationship between the structure and function of agarase.