Directed evolution of a D-mandelate dehydrogenase toward D-o-chloromandelic acid and insight into the molecular basis for its catalytic performance

Halogenated mandelate and its derivatives are important scaffolds in chemical industry. However, the natural D -mandelate dehydrogenase (DMDH) showed relatively low catalytic activity toward D -o-chloromandelic acid, which largely limits the efficiency of dehydrogenation processes. To improve catalytic activity of Lactobacillus brevis D -mandelate dehydrogenase ( Lb DMDH) toward halogenated substrate, a D -mandelate dehydrogenase mutant Lb DMDH N253S with higher catalytic activity toward D -o-chloromandelic acid was successfully obtained by directed evolution, which was about 29 times of Lb DMDH. In addition, the temperature optimum of Lb DMDH N253S is 50 °C, and closer to the optimal growth temperature for Escherichia coli , indicating that it may be more advantageous in whole cell catalysis using living cells as catalysts. Meanwhile, the K cat value toward D -o-chloromandelic acid of Lb DMDH N253S is 2.08 s −1 , which is significantly higher than the one (0.09 s −1 ) of Lb DMDH, indicating that Lb DMDH N253S displayed higher catalytic efficiency toward D -o-chloromandelic acid. Then, we preliminarily explained the molecular basis for its catalytic performance by in silico design methods. All of these results established a solid foundation for molecular modification of DMDHs and the other industrial enzymes.