“Nonpolarity paving” in substrate tunnel of a Limnobacter sp. Phenylacetone monooxygenase for efficient single whole-cell synthesis of esomeprazole

Baeyer-Villiger monooxygenase (BVMO) mediated sulfoxidation is a sustainable approach for the synthesis of esomeprazole. In this work, a novel phenylacetone monooxygenase from Limnobacter sp. (LnPAMO) was found to have trace activity for synthesis of enantiopure esomeprazole. Through engineering in the substrate tunnel using a mutagenesis strategy called "nonpolarity paving" and some modifications in cofactor binding domains, a mutant harboring 15 mutations (LnPAMO Mu15) was obtained with 6.6 × 103-fold higher activity to convert omeprazole sulfide into esomeprazole. The activities of the mutant for synthesis of (S)-methyl phenyl sulfoxide and (S)-pantoprazole also increased much, indicating the versatility of the mutant for sulfoxide synthesis. Importantly, no over-oxidation byproduct omeprazole sulfone was detected in the sulfoxidation products by both mass spectrometry and HPLC analysis. Then NADP-dependent Burkholderia stabili formate dehydrogenase was ligated behind Mu15 along with a ribosome binding site sequence in pET-28a for co-expression. By single whole-cell of recombinant Escherichia coli BL21 coexpressing Mu15 and formate dehydrogenase, omeprazole sulfide was efficiently converted into esomeprazole without production of sulfone (16 g/L substrate, enantiomeric excess > 99.9% (S) and > 99% conversion) and the space–time-yield reached 1.67 g product/L/h.