Acetoacetyl-CoA reductase PhaB as an excellent anti-Prelog biocatalyst for the synthesis of chiral β-hydroxyl ester and the molecular basis of its catalytic performance

Abstract Acetoacetyl-CoA reductase PhaB turned out to be capable of catalyzing the anti-Prelog asymmetric reduction of various β-ketoesters (1a-12a) and aromatic ketones (13a-29a). Particularly, PhaB showed high specific activity and excellent stereoselectivity (93.0%-99.8% eep) toward β-ketoesters. The specific activity of PhaB toward ethyl 4-chloroacetoacetate 11a was up to 1302.2 mU/mg. The molecular basis analysis showed the rotatable single bonds in β-ketoesters endow them with a high degree of structural flexibility and adaptability. Thus, β-ketoesters could quickly adjust their conformation and further form a productive conformation in the narrow substrate-binding pocket of the enzyme. In contrast, PhaB exhibited low specific activity and stereoselectivity toward the majority of aromatic ketones. The large steric hindrance and rigid structure resulted from aromatic rings made the aromatic ketones impossible to adjust their conformation as conveniently as β-ketoesters. Furthermore, it was found the halogen bond was the major driven force of the high specific activity of PhaB toward chlorinated β-ketoesters (10a and 11a), while the distribution of enzyme-substrate interactions was an important factor determining the enzyme activity besides the steric hindrance. Moreover, the geometric configuration of the substrate and the enzyme substrate-binding pocket played critical roles in determining the substrate binding mode and the enzyme stereoselectivity.