Traditional screening methods of enzyme engineering often require building large mutant libraries to screen for potentially beneficial sites, which are often time-consuming and labor-intensive with low mining efficiency. In this study, a novel enzyme engineering strategy was established to modify carbonyl reductase Ls CR for the synthesis of (1 S )-2-chloro-1-(3,4-difluorophenyl) ethanol (( S )-CFPL), which is a key intermediate of anticoagulant drug ticagrelor. The strategy was developed by combining HotSpot, FireProt and multiple sequence alignment, resulting in the construction of a “small and smart” mutant library including 10 mutations. Among them, 5 mutations were positive, resulting in a 50% mining accuracy of beneficial sites. Finally, a highly active mutant Ls CR M3 (N101D/A117G/F147L) was obtained by further screening through saturation mutation and iterative mutation. Compared with wild type (WT) Ls CR, the catalytic activity of Ls CR M3 was increased by 4.7 times, the catalytic efficiency k cat / K M value was increased by 2.9 times, and the half-life t 1/2 at 40 °C was increased by 1.3 times. Due to the low aqueous solubility of the substrate 2-chloro-1-(3,4-difluorophenyl) ethanone (CFPO), isopropanol was used as not only the co-substrate but also co-solvent. In the presence of 40% ( v / v ) isopropanol, Ls CR M3 completely reduced 400 g/L CFPO to enantiomerically pure CFPL (99.9%, e.e. ) in 11 h with a space–time yield (STY) as high as 809 g/L∙d.
Carbonyl reductases are useful for producing optically active alcohols from their corresponding prochiral ketones. Herein, we applied a computer-assisted strategy to increase the thermostability of a previously constructed carbonyl reductase, Ls CR M4 (N101D/A117G/F147L/E145A), which showed an outstanding activity in the synthesis of the ticagrelor precursor (1 S )-2-chloro-1-(3,4-difluorophenyl)ethanol. The stability changes introduced by mutations at the flexible sites were predicted using the computational tools FoldX, I-Mutant 3.0, and DeepDDG, which demonstrated that 12 virtually screened mutants could be thermally stable; 11 of these mutants exhibited increased thermostability. Then a superior mutant Ls CR M4 -V99L/D150F was screened out from the library that was constructed by iteratively combining the beneficial sites, which showed a 78% increase in activity and a 17.4°C increase in melting temperature compared to Ls CR M4 . Our computer-assisted design and combinatorial strategy dramatically increased the efficiency of thermostable enzyme production.
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