- Single-Point Mutant Inverts the Stereoselectivity of a Carbonyl Reductase toward β-Ketoesters with Enhanced Activity
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Enzyme stereoselectivity control is still a major challenge. To gain insight into the molecular basis of enzyme stereo-recognition and expand the source of antiPrelog carbonyl reductase toward β-ketoesters, rational enzyme design aiming at stereoselectivity inversion was performed. The designed variant Q139G switched the enzyme stereoselectivity toward β-ketoesters from Prelog to antiPrelog, providing corresponding alcohols in high enantiomeric purity (89.1–99.1 % ee). More importantly, the well-known trade-off between stereoselectivity and activity was not found. Q139G exhibited higher catalytic activity than the wildtype enzyme, the enhancement of the catalytic efficiency (kcat/Km) varied from 1.1- to 27.1-fold. Interestingly, the mutant Q139G did not lead to reversed stereoselectivity toward aromatic ketones. Analysis of enzyme–substrate complexes showed that the structural flexibility of β-ketoesters and a newly formed cave together facilitated the formation of the antiPrelog-preferred conformation. In contrast, the relatively large and rigid structure of the aromatic ketones prevents them from forming the antiPrelog-preferred conformation.
- Li, Aipeng,Wang, Ting,Tian, Qing,Yang, Xiaohong,Yin, Dongming,Qin, Yong,Zhang, Lianbing
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p. 6283 - 6294
(2021/03/16)
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- Fine-tuning of the substrate binding mode to enhance the catalytic efficiency of an: Ortho -haloacetophenone-specific carbonyl reductase
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Carbonyl reductase BaSDR1 has been identified as a potential ortho-haloacetophenone-specific biocatalyst for the synthesis of chiral 1-(2-halophenyl)ethanols due to its excellent stereoselectivity. However, the catalytic efficiency of BaSDR1 is far below the required level for practical applications. Thus, fine-tuning of the substrate binding mode, which aimed at maximum preservation of the positive factors for substrate specificity and stereoselectivity, was proposed as a tentative strategy for enhancing its catalytic efficiency. The designed mutants Q139S, D253Y and Q139S/D253Y showed significantly enhanced catalytic efficiency. Remarkably, the variants Q139S and Q139S/D253Y exhibited a more than 9-fold improvement in catalytic efficiency (kcat/Km) toward substrates 6a and 11a, respectively. More importantly, none of the variants caused activity-stereoselectivity trade-off and all variants exhibited excellent stereoselectivity (99% ee). Analysis of variant-substrate complexes showed that the mutations indeed enable the fine-tuning of the substrate binding mode. New strengthening factors for consolidating the productive conformation were introduced while the original positive factors were preserved. Furthermore, at a substrate concentration of 100 mM, recombinant E. coli whole cells expressing the BaSDR1 mutants were successfully applied to the synthesis of several key intermediates of chiral pharmaceuticals, including (S)-1-(2-chlorophenyl)ethanol, (S)-1-(2,4-difluorophenyl)ethanol and (S)-1-(2,6-difluorophenyl)ethanol, with 99% enantiomeric excess, and the conversion reached over 95% in a certain period of time. These results demonstrated the effectiveness of the strategy involving the fine-tuning of the substrate binding mode and the applicability of the designed mutants in efficient reduction of ortho-haloacetophenones.
- Li, Aipeng,Li, Xue,Pang, Wei,Tian, Qing,Wang, Ting,Zhang, Lianbing
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p. 2462 - 2472
(2020/05/13)
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