Enzymatic reduction of levulinic acid by engineering the substrate specificity of 3-hydroxybutyrate dehydrogenase

Enzymatic reduction of levulinic acid (LA) was performed for the synthesis of 4-hydroxyvaleric acid (4HV) – a monomer of bio-polyester and a precursor of bio-fuels – using 3-hydroxybutyrate dehydrogenase (3HBDH) from Alcaligenes faecalis. Due to the catalytic inactivity of the wild-type enzyme toward LA, engineering of the substrate specificity of the enzyme was performed. A rational design approach with molecular docking simulation was applied, and a double mutant, His144Leu/Trp187Phe, which has catalytic activity (kcat/Km = 578.0 min−1 M−1) toward LA was generated. Approximately 57% conversion of LA to 4HV was achieved with this double mutant in 24 h, while no conversion was achieved with the wild-type enzyme.