A Crystal Structure of the R-Amine Transaminase from Arthrobacter for Asymmetric Catalysis of Chiral Amines

Abstract

Pure chiral amines are crucial building blocks in the synthesis of some pharmaceutical drugs, agrochemical and other chemical compounds. Amine transaminases (ATAs) have been paid increasing attention as useful tools for efficient chiral-amine production. In particular, R-stereospecific ATA (R-ATA) is quite valuable and gains more benefit as industrial catalysts. Gabaculine is a common suicide inhibitor of ATAs. R-ATA is also inhibited by gabaculine. In order to guide the protein engineering of transaminases to improve substrate specificity and enantioselectivity, we carried out a crystal structural analysis of the R-ATA from Arthrobacter with the bound inhibitor gabaculine. Mechanistic studies and crystal structures have shown that (1) gabaculine binds to the aminotransferase enzyme, forming a Schiff base with the PLP cofactor; (2) the proton abstraction of this external aldimne yields an unstable intermediate which is then converted to extremely stable and irreversible m-carboxyphenylpyridoxamine phosphate (mCPP). Also the complex offers detailed insight into the structural basis for substrate specificity and enantioselectivity of the industrial application of R-ATAs.