Identification of novel thermostable taurine-pyruvate transaminase from Geobacillus thermodenitrificans for chiral amine synthesis

摘要

omega-Transaminases (omega-TAs) are one of the most popular candidate enzymes in the biosynthesis of chiral amines. Determination of yet unidentified omega-TAs is important to broaden their potential for synthetic application. Taurine-pyruvate TA (TPTA, EC 2.6.1.77) is an omega-TA belonging to class III of TAs. In this study, we cloned a novel thermostable TPTA from Geobacillus thermodenitrificans (TPTA(gth)) and overexpressed it in Escherichia coli. The enzyme showed the highest activity at pH 9.0 and 65 A degrees C, with remarkable thermostability and tolerance toward organic solvents. Its K (M) and v (max) values for taurine were 5.3 mM and 0.28 mu mol s(-1) mg(-1), respectively. Determination of substrate tolerance indicated its broad donor and acceptor ranges for unnatural substrates. Notably, the enzyme showed relatively good activity toward ketoses, suggesting its potential for catalyzing the asymmetric synthesis of chiral amino alcohols. The active site of TPTA(gth) was identified by performing protein sequence alignment, three-dimensional structure simulation, and coenzyme pyridoxamine phosphate docking. The protein sequence and structure of TPTA(gth) were similar to those of TAs belonging to the 3N5M subfamily. Its active site was found to be its special large pocket and substrate tunnel. In addition, TPTA(gth) showed a unique mechanism of sulfonate/alpha-carboxylate recognition contributed by Arg163 and Gln160. We also determined the protein sequence fingerprint of TPTAs in the 3N5M subfamily, which involved Arg163 and Gln160 and seven additional residues from 413 to 419 and lacked Phe/Tyr22, Phe85, and Arg409.