Functional characterization and structure-guided engineering of a thermostable (S)-selective amine transaminase from Streptomyces sp. BV333

Amine transaminases (ATAs) are PLP-dependent enzymes that catalyze the stereoselective transfer of an amino group from an amino donor to prochiral ketone substrates, making them attractive biocatalytic tools for the synthesis of optically pure chiral amines. Recently, our group identified an (S)-selective amine transaminase, Sbv333-ATA, in the genome of Streptomyces sp. BV333, a strain isolated from the rhizosphere of Salvia pratensis at the University of Belgrade. This enzyme exhibits remarkable thermostability and broad substrate specificity toward various amino acceptors [1,2]. In the present work, Sbv333-ATA was further functionally investigated and structurally characterized to assess its biocatalytic potential. High-resolution crystal structures were solved for the native enzyme as well as for complexes with substrates and the inhibitor gabaculine. Structure-guided rational mutagenesis was subsequently employed to modulate substrate specificity. Among the generated variants, the W89A mutant showed significantly enhanced activity toward bulky substrates, highlighting its potential for further engineering. Overall, these results pave the way for the development of Sbv333-ATA as a versatile and robust biocatalyst for asymmetric synthesis [3].