Sortase A介导的(S)-羰基还原酶Ⅱ寡聚体高效立体选择性转化(S)-苯基乙二醇

Sortase A-mediated oligomers of (S)-carbonyl reductase Ⅱ suitable for biotransformation of (S)-phenyl-1,2-ethanediol

【目的】以金黄色葡萄球菌(Staphylococcus aureus)的sortase A为"分子订书机",用于(S)-羰基还原酶Ⅱ分子之间的连接,获得催化功能与稳定性增强的氧化还原酶寡聚体,高效催化2-羟基苯乙酮,合成(S)-苯基乙二醇。【方法】从S.aureus基因组中克隆sortase A基因,在大肠杆菌中表达,通过镍柱和凝胶层析纯化重组酶,获得纯酶sortase A。通过基因工程手段在(S)-羰基还原酶Ⅱ的C末端添加GGGGSLPETGG序列,蛋白纯化获得(S)-羰基还原酶Ⅱ-GGGGSLPETGG,摸索了sortase A催化(S)-羰基还原酶Ⅱ-GGGGSLPETGG的分子连接,形成(S)-羰基还原酶Ⅱ寡聚体的最佳条件,并研究了寡聚体酶学性质及生物转化(S)-苯基乙二醇的效率。【结果】(S)-羰基还原酶Ⅱ寡聚体比酶活力为38.5 U/mg,比原始型(S)-羰基还原酶Ⅱ提高了6倍,最适反应温度为50°C,最适pH为6.0,在50°C放置1 h后酶活仍旧保持90%以上;蛋白质变性实验结果显示,(S)-羰基还原酶Ⅱ寡聚体的变性温度为60.1°C,比原始酶提高了10°C;生物转化结果显示(S)-羰基还原酶Ⅱ寡聚体在3 h内完全转化5 g/L 2-羟基苯乙酮,产生光学纯度为100%的(S)-苯基乙二醇,相比于重组大肠杆菌(S)-羰基还原酶Ⅱ全细胞催化时间缩短了16倍。【结论】本研究首次将sortase A应用于氧化还原酶的分子连接,显著提高了酶的催化效率和热稳定性,表明sortase在手性催化中有很大的潜在应用价值。

[Objective] To obtain oligomers of（S）-carbonyl reductase Ⅱ with strong activity and stability, we used sortase A from Staphylococcus aureus as molecular ＂stapler＂ to conjugate（S）-carbonyl reductase Ⅱ. The（S）-carbonyl reductase Ⅱ oligomers efficiently catalyzed the biotransformation of 2-hydroxyacetophenone to（S）-1-phenyl-1,2-ethanediol. [Methods] We cloned sortase A gene from S. aureus genome and expressed it in Escherichia coli. The recombinant enzyme was purified through Ni-affinity and gel filtration chromatography. Meanwhile, we added GGGGSLPETGG to C terminus of（S）-carbonyl reductase Ⅱ using genetic techniques, and purified recombinant SCRⅡ-GGGGSLPETGG to homogeneity. We determined the optimal reaction conditions of sortase A-mediated ligation of（S）-carbonyl reductase Ⅱ to oligomers. The enzyme characteristics of the generated oligomers were studied. And the oligomers-catalyzed biotransformation efficiency of（S）-1-phenyl-1,2-ethanediol was further detected. [Results] Oligomers showed a specific activity of 38.5 U/mg, 6-fold increase compared to（S）-carbonyl reductase Ⅱ. The optimal temperature and pH of ligation reaction by oligomers were 35 °C and 6.0 respectively. The relative activity was maintained over 90% at 50 °C for 1 hour. Denaturation test showed that the denaturation temperature of oligomers was 60.1 °C, 10 °C higher than that of（S）-carbonyl reductase Ⅱ. Biotransformation results indicated that oligomers completely transformed 5 g/L 2-hydroxyacetophenone within 3 hours to generate（S）-1-phenyl-1,2-ethanediol with an optical purity of 100%. With oligomers, we reduced transformation duration for 16 folds compared to that of recombinant E. coli-（S）-carbonyl reductase Ⅱ cells. [Conclusion] This work first described sortase A-mediated the ligation of oxidoreductase and significantly improved catalytic efficiency and thermal stability of enzyme, suggesting sortase had great potential application in chiral synthesis.