Electric fields enhance Diels–Alderase catalysis in Abyssomicin C biosynthesis

Natural Diels–Alderases help catalyze [4+2] cycloadditions by preorganizing substrates into reactive conformations. However, the role of other catalytic factors, such as electrostatic effects, remain elusive. Here, we combine conceptual Density Functional Theory (CDFT) descriptors and electric field analysis to unravel the electrostatic basis of activity in the Diels-Alderase AbyU. Previously, four different enzyme-substrate poses were identified by docking, of which two showed catalytically favorable free energy barriers based on quantum mechanical/molecular mechanical (QM/MM) reaction simulations. Here, we show that atom-condensed Fukui functions can predict the reactivity based on reactant conformations only, based on the diene carbons involved in bond formation. The importance of the enzyme-diene interaction is supported by electric field analysis, which shows how reactivity of enzyme-substrate poses correlates with aligment of the enzyme field along the diene moiety. Our findings establish a basis for predicting and engineering Diels–Alderase activity based on electrostatic and electronic reactivity features.