Secretory expression of cyclohexanone monooxygenase by methylotrophic yeast for efficient omeprazole sulfide bio-oxidation

Improving the Enantioselectivity of CHMOBrevi1 for Asymmetric Synthesis of Podophyllotoxin Precursor

(R)-β-piperonyl-γ-butyrolactones are key building blocks for the synthesis of podophyllotoxin, which have demonstrated remarkable potential in cancer treatment. Baeyer-Villiger monooxygenases (BVMOs)-mediated asymmetric oxidation is a green approach to produce chiral lactones. While several BVMOs were able to oxidize the corresponding cyclobutanone, most BVMOs gave the (S) enantiomer while Cyclohexanone monooxygenase (CHMO) from Brevibacterium sp. HCU1 gave (R) enantiomer, but with a low enantioselectivity (75 % ee). In this study, we use a strategy called "focused rational iterative site-specific mutagenesis" (FRISM) at residues ranging from 6 Å from substrate. The mutations by using a restricted set of rationally chosen amino acids allow the formation of a small mutant library. By generating and screening less than 60 variants, we achieved a high ee of 96.8 %. Coupled with the cofactor regeneration system, 9.3 mM substrate was converted completely in a 100-mL scale reaction. Therefore, our work reveals a promising synthetic method for (R)-β-piperonyl-γ-butyrolactone with the highest enantioselectivity, and provides a new opportunity for the chem-enzymatic synthesis of podophyllotoxin.

Colorimetric high-throughput screening method for directed evolution of prazole sulfide monooxygenase

Baeyer-Villiger monooxygenases (BVMOs) are important biocatalysts for the enzymatic synthesis of chiral sulfoxides, including chiral sulfoxide-type drugs proton pump inhibitors for the treatment of gastrointestinal diseases. However, native BVMOs are not yet suitable for practical application due to their unsatisfactory activity and thermostability. Although protein engineering approaches can help address these issues, few feasible high-throughput methods are available for the engineering of such enzymes. Herein, a colorimetric detection method to distinguish sulfoxides from sulfides and sulfones was developed for prazole sulfide monooxygenases . Directed evolution enabled by this method has identified a prazole sulfide monooxygenase CbBVMO variant with improved activity and thermostability in catalyzing the asymmetric oxidation of lansoprazole sulfide. A 71.3% increase in conversion and 6°C enhancement in the melting point were achieved compared with the wild-type enzyme. This new method is feasible for high-throughput screening of prazole sulfide monooxygenases variants with improved activity, thermostability, and/or substrate specificity.