Altering the substrate specificity and enantioselectivity of phenylacetone monooxygenase by structure-inspired enzyme redesign

Of all presently available Baeyer-Villiger monooxygenases, phenylacetone monooxygenase (PAMO) is the only representative for which a structure has been determined. While it is an attractive biocatalyst because of its thermostability, it is only active with a limited number of substrates. By means of a comparison of the PAMO structure and a modeled structure of the sequence-related cyclopentanone monooxygenase, several active-site residues were selected for a mutagenesis study in order to alter the substrate specificity. The M446G PAMO mutant was found to be active with a number of aromatic ketones, amines and sulfides for which wild-type PAMO shows no activity. An interesting finding was that the mutant is able to convert indole into indigo blue: a reaction that has never been reported before for a Baeyer-Villiger monooxygenase. In addition to an altered substrate specificity, the enantioselectivity towards several sulfides was dramatically improved. This newly designed Baeyer-Villiger monooxygenase extends the scope of oxidation reactions feasible with these atypical monooxygenases.