Engineering of Thermostable β-Hydroxyacid Dehydrogenase for the Asymmetric Reduction of Imines.

The β-hydroxyacid dehydrogenase from Thermocrinus albus (Ta-βHAD), which catalyzes the NADP+ -dependent oxidation of β-hydroxyacids, was engineered to accept imines as substrates. The catalytic activity of the proton-donor variant K189D was further increased by the introduction of two nonpolar flanking residues (N192 L, N193 L). Engineering the putative alternative proton donor (D258S) and the gate-keeping residue (F250 A) led to a switched substrate specificity as compared to the single and triple variants. The two most active Ta-βHAD variants were applied to biocatalytic asymmetric reductions of imines at elevated temperatures and enabled enhanced product formation at a reaction temperature of 50 °C.