Biotechnology and Bioengineering, Vol.118, No.11, 4441-4452, 2021
Semirational engineering of an aldo-keto reductase KmAKR for overcoming trade-offs between catalytic activity and thermostability
Enzyme engineering usually generates trade-offs between activity, stability, and selectivity. Herein, we report semirational engineering of an aldo-keto reductase (AKR) KmAKR for simultaneously enhancing its thermostability and catalytic activity. Previously, we constructed KmAKR(M9) (W297H/Y296W/K29H/Y28A/T63M/A30P/T302S/N109K/S196C), which showed outstanding activity towards t-butyl 6-chloro-(3R,5S)-dihydroxyhexanoate ((3R,5S)-CDHH), and t-butyl 6-cyano-(3R,5R)-dihydroxyhexanoate, the key chiral building blocks of rosuvastatin and atorvastatin. Under the guidance of computer-aided design including consensus residues analysis and molecular dynamics (MD) simulations, K164, S182, S232, and Q266 were dug out for their thermostability conferring roles, generating the "best" mutant KmAKR(M13)(W297H/Y296W/K29H/Y28A/T63M/A30P/T302S/N109K/S196C/K164E/S232A/S182H/Q266D). The T-m and T-50(15) values of KmAKR(M13) were 10.4 and 6.1 degrees C higher than that of KmAKR(M9), respectively. Moreover, it displayed a significantly elevated organic solvent tolerance over KmAKR(M9). Structural analysis indicated that stabilization of the alpha-helixes mainly contributed to thermostability enhancement. Under the optimized conditions, KmAKR(M13) completely asymmetrically reduced 400 g/l t-butyl 6-chloro-(5S)-hydroxy-3-oxohexanoate ((5S)-CHOH) in 8.0 h at a high substrate to catalyst ratio (S/C) of 106.7 g/g, giving diastereomerically pure (3R,5S)-CDHH (>99.5% d.e.(P)) with a space-time yield (STY) of 449.2 g/l center dot d.