Activity Improvements of an Engineered ω-transaminase for Ketones Are Positively Correlated with Those for Cognate Amines

Chiral amines are broadly used as essential building blocks of diverse pharmaceutical drugs. ω-Transaminase (ω-TA) is one of the promising enzymes for biocatalytic preparation of chiral amines owing to its capability for reductive amination of ketones. However, industrial application of ω-TA to asymmetric synthesis of chiral amines is often limited by marginal activities for ketones. Here, we explore whether activity improvements of ω-TA for ketones caused by active site engineering are correlated with those for cognate amines. We examined amino donor reactivities of 20 amines with ω-TA from Ochrobactrum anthropi (OATA) and its engineered variant carrying a W58L mutation (OATA_W58L). Consistent with the previously observed activity increases for ketones, OATA_W58L showed 3 to 79-fold activity improvements for amines. Docking simulations suggested that the activity improvements resulted from increased proximity of a bound amine to an internal aldimine owing to relocation of a small binding pocket. Activity comparison indicated that the W58L mutation induced activity increases for ketones better than it did those for amines. This result motivated us to carry out Pearson correlation analysis among the activity improvements for amines and ketones, revealing a strong positive correlation (r = 0.84). This suggests that active site engineering beneficial for activity of ω-TA toward a target amine is likely to evoke an activity improvement for its cognate ketone. Our finding is expected to provide a clue to design a robust high-throughput screening method required for creation of an engineered mutant displaying a better activity toward a target ketone.