Improving Toluene Dioxygenase Activity for Ester-Functionalized Substrates through Enzyme Engineering

Rieske dioxygenases have a history of utility in organic synthesis, owing to their ability to catalyze the asymmetric dihydroxylation of aromatics to produce chiral diene-diol metabolites. However, their utility as green-chemical tools has been limited by steric and electronic constraints on their substrate scopes and their activity. Herein we report the rational engineering of a widely used Rieske dioxygenase, toluene dioxygenase (TDO), to improve the activity of this enzyme system for the dihydroxylation of a synthetically valuable substrate class for which the wild-type enzyme possesses low activity, the ester-functionalized aromatics. Through active site targeted mutagenesis and application of a recently reported high throughput screening platform, engineered TDO variants with significantly increased activity in the dihydroxylation of these valuable substrates were identified and characterized, revealing key active site residues that modulate the enzyme's activity and selectivity.