Rational engineering of R-selective transaminase from Pseudonocardia ammonioxydans for efficient synthesis of chiral...

R-transaminases show significant promise for the industrial synthesis of chiral amine pharmaceutical intermediates. However, the application is hindered by limited substrate acceptance and poor catalytic efficiency toward bulky substrates. Herein, the R-transaminase from Pseudonocardia ammonioxydans (PaTA) with the high activity towards the mexiletine precursor ketone (1c) was identified, and its crystal structure was resolved (PDB: 9UJD). Substrate specificity analysis revealed that PaTA exhibited obvious substrate preference for aryl-substituted phenoxyacetones (1c-16c). Based on the crystal structure, key sites affecting substrate selectivity were identified, followed by multiple rounds of engineering that yielded a series of variants with enhanced catalytic performance. Ultimately, the gram-scale synthesis of R-1d and 12d was conducted, achieving the space-time yields (STY) of 24 and 32 g/L·h, respectively. This study provides practical biocatalysts for the synthesis of chiral β-amino aryl ethers, along with insights into the relationship between the enzyme-substrate binding pocket and substrate selectivity.