Active-site engineering of ω-transaminase from Ochrobactrum anthropi for preparation of L-2-aminobutyric acid

Background: The unnatural amino acid, L-2-aminobutyric acid (L-ABA) is an essential chiral building block for various pharmaceutical drugs, such as the antiepileptic drug levetiracetam and the antituberculosis drug ethambutol. The present study aims at obtaining variants of omega-transaminase from Ochrobactrum anthropi (OATA) with high catalytic activity to alpha-ketobutyric acid through protein engineering. Results: Based on the docking model using alpha-ketobutyric acid as the ligand, 6 amino acid residues, consisting of Y20, L57, W58, G229, A230 and M419, were chosen for saturation mutagenesis. The results indicated that L57C, M419I, and A230S substitutions demonstrated the highest elevation of enzymatic activity among 114 variants. Subsequently, double substitutions combining L57C and M419I caused a further increase of the catalytic efficiency to 3.2-fold. This variant was applied for threonine deaminase/OATA coupled reaction in a 50-mL reaction system with 300 mM L-threonine as the substrate. The reaction was finished in 12 h and the conversion efficiency of L-threonine into L-ABA was 94%. The purity of L-ABA is 75%, > 99% ee. The yield of L-ABA was 1.15 g. Conclusion: This study provides a basis for further engineering of omega-transaminase for producing chiral amines from keto acids substrates.

Automated summary

This study successfully obtained OATA variants with high catalytic activity, which were applied in a reaction system to produce the chiral amine molecule L-ABA with a conversion efficiency of 94%.