Enantioselectivity and key residue of Herbaspirillum huttiense monooxygenase in asymmetric epoxidation of styrenes

Styrene monooxygenases (SMOs) are powerful enzymes for the synthesis of enantiopure epoxides, but these SMOs have narrow substrate spectra, and the residues in controlling enantioselectivity of SMOs remains unclear. A monooxygenase from Herbaspirillum huttiense (HhMO) was found to have excellent enantioselectivities and diastereoselectivities in the epoxidation of unconjugated terminal alkenes. Here we found that HhMO could also transfer styrene into styrene epoxide with 75% ee, and it could also catalyze the epoxidation of styrene derivatives into the corresponding epoxides with enantioselectivities up to 99% ee. Meanwhile, site 199 in the substrate access channel of HhMO was found to play an important role in the controlling enantioselectivity of the epoxidation. The E199L variant catalyzed the epoxidation of styrene with > 99% ee. The identification of critical residue that affects the enantioselectivity of SMOs would thus be valuable for creating efficient monooxygenases for the preparation of essential enantiopure epoxides.

Automated summary

This study found that the monooxygenase HhMO from Herbaspirillum huttiense has excellent enantioselectivity and diastereoselectivity, and can catalyze the epoxidation reaction efficiently. The study also identified the important role of site 199 in the substrate access channel of HhMO in controlling enantioselectivity.