Expanding the L-threonine transaldolase toolbox for the diastereomeric synthesis of -hydroxy--amino acids

L-threonine transaldolases (LTTA) catalyze the stereoselective synthesis L-threonine and aldehydes to beta-hydroxy-alpha-amino acids (beta HAAs). The few sources of discovered LTTAs with good characteristics restricted their possible applicability. Here we mined and characterized three new PLP-dependent LTTAs from Burkholderia diffusa (BuLTTA), Pseudomonas sp. (PslLTTA) and Chitiniphilus shinanonensis (ChLTTA). Three LTTAs were all pHsensitive enzymes with high temperature tolerance, and Ca2+ and Mg2+ promoted the enzyme activities. They could catalyze L-threonine as the donor substrate and a variety of aromatic aldehydes as the acceptor substrates with different catalytic efficiencies. The molecular dynamics simulation showed the variation of interaction force of conserved residues around the ligand led to the different catalytic efficiency of ChLTTA for the acceptor substrates. The recombinant ChLTTA whole-cells catalyzed the synthesis of L-threo-p-methylsulfonyl phenylserine (L-threo-16b) and received a high yield of 73.2% and a diastereoselectivity of 85.9% within 6 h under optimized conditions.This work discovered three LTTAs and demonstrated their potential in beta HAAs synthesis, which will provide new biocatalytic materials for the industrial production of beta HAAs.