Semi-rational engineering of ω-transaminase for enhanced enzymatic activity to 2-ketobutyrate

Transaminases (EC 2.6.1.X, TAs) are important biocatalysts in the synthesis of chiral amines, and have significant value in the field of medicine. However, TAs suffer from low enzyme activity and poor catalytic efficiency in the synthesis of chiral amines or non-natural amino acids, which hinders their industrial applications. In this study, a novel TA derived from Paracoccus pantotrophus (ppTA) that was investigated in our previous study was employed with a semi-rational design strategy to improve its enzyme activity to 2-ketobutyrate. By using homology modeling and molecular docking, four surrounding sites in the substrate-binding S pocket were selected as potential mutational sites. Through alanine scanning and saturation mutagenesis, the optimal mutant V153A with significantly improved enzyme activity was finally obtained, which was 578 % higher than that of the wild-type ppTA (WT). Furthermore, the mutant enzyme ppTA-V153A also exhibited slightly improved temperature and pH stability compared to WT. Subsequently, the mutant was used to convert 2-ketobutyrate for the preparation of L-2-aminobutyric acid (L-ABA). The mutant can tolerate 300 mM 2-ketobutyrate with a conversion rate of 74 %, which lays a solid foundation for the preparation of chiral amines.