Asymmetric reduction of conjugated C[dbnd]C bonds by immobilized fusion of old yellow enzyme and glucose dehydrogenase

Abstract

Asymmetric reduction of the conjugated CC bonds by the old yellow enzymes (OYEs) presents a promising field in the synthesis of chiral chemicals. Nevertheless, few natural OYEs have been applied in large-scale applications due to the requirement of costly NADPH and low operational stability. Herein, a stable and efficient fusion of YqjM from Bacillus subtilis and glucose dehydrogenase (GDH) from Bacillus megaterium was constructed to stereoselectively reduce the conjugated CC bonds in a self-sufficient continuous process. The effects of the enzyme order and different linkers on the fusions were investigated by structural analysis and all-atom molecular dynamics simulation. The best fusion YqjM_G_GDH gave 98% conversion of 100 ​mmol/L 2-methylcyclopentenone with an excellent ee value (>99%) in 3 ​h, while the mixture of individual enzymes only obtained 68% conversion after more than 8 ​h. The improved substrate conversion of YqjM_G_GDH fusion was probably attributed to the increased flexibility of each fused enzyme and the shortening of the diffusion distance of NADPH regenerated. A one-pot process was designed to purify and immobilize the fusion on the Ni2+-nitrilotriacetic acid functionalized magnetic mesoporous silica nanoflowers. The resulting immobilized biocatalyst not only catalyzed the asymmetric reduction of various α,β-unsaturated ketones (20 ​mmol/L) continuously with only 50 ​μmol/L NADP+ to initiate the whole process, but also retained more than 82% of the initial activity after seven cycles, serving as a good candidate for the industrial applications.