Pseudomonas geniculata D-甘露糖异构酶的热稳定性改造及发酵优化

Thermal Stability Modification and Fermentation Optimization of Pseudomonas geniculata D-mannose Isomerase

为了提高重组弯曲假单胞菌(Pseudomonas geniculata)D-甘露糖异构酶的热稳定性,对其进行了定点突变,获得了热稳定性提高了75%的突变体C126A/E402W。并进一步探讨了3-L发酵罐不同诱导温度对重组大肠杆菌菌体生长及产酶的影响。结果表明:重组大肠杆菌最优3-L发酵罐培养诱导温度为25℃。在此条件下得到的最高酶活为2535197 U/mL,总蛋白浓度约为50 g/L。为了探索该重组菌株表达量较高的原因,进一步进行了蛋白质解折叠/重折叠的研究。研究发现,蛋白质重折叠速率慢有助于其正确折叠,可溶性表达量更高;蛋白质重折叠速率过快可能导致蛋白质在表达过程中错误折叠并形成大量包涵体,表达量低。

In order to improve the thermostability of Pseudomonas geniculata D-mannose isomerase,A mutant C126A/E402W with a 75%increase in thermal stability was obtained by site-directed mutagenesis.Furthermore,the effects of different induction temperatures of 3-L fermenters on the growth and enzyme production of recombinant Escherichia coli were investigated.The results showed that the optimum induction temperature of the recombinant Escherichia coli 3-L fermenter was 25℃.The highest enzyme activity obtained under these conditions was 2535197 U/mL and the total protein concentration reached 50 g/L.In order to explore the reason for the high expression level of the recombinant D-mannose isomerase,further studies on protein unfolding/refolding were conducted.The study found that the slow rate of protein refolding helps its correct folding,and the soluble expression is higher.The protein refolding rate is too fast,which may cause the protein to fold incorrectly during expression and form a large number of inclusion bodies with low expression.