Mining and tailor-made engineering of a novel keto reductase for asymmetric synthesis of structurally hindered γ- and δ-lactones

A novel carbonyl reductase from Hyphopichia burtoni ( Hb KR) was discovered by gene mining. Hb KR is a NADPH-dependent dual function enzyme with reduction and oxidation activity belonging to SDR superfamily. Hb KR strictly follows Prelog priority in the reduction of long-chain aliphatic keto acids/esters containing remote carbonyl groups, such as 4-oxodecanoic acid and 5-oxodecanoic acid, producing ( S )- γ -decalactone and ( S )- δ -decalactone in >99 % e.e. Tailor-made engineering of Hb KR was conducted to improve its catalytic efficiency . Variant F207A/F86M was obtained with specific activity of 8.37 U/mg toward 5-oxodecanoic acid, which was 9.7-fold of its parent. Employing F207A/F86M, 100 mM 5-oxodecanoic acid could be reduced into optically pure ( S )- δ -decalactone. Molecular docking analysis indicates that substitution of aromatic Phe with smaller residues renders sufficient space for accommodating substrates in a more stable conformation. This study offers an efficient biocatalyst for the biosynthesis of ( S )-lactones, and provides guidance for engineering carbonyl reductases toward structurally hindered substrates.