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The Catalytic Mechanism of a Natural Diels–Alderase Revealed in Molecular Detail

Byrne, Matthew J., Lees, Nicholas R., Han, Li-Chen, van der Kamp, Marc W., Mulholland, Adrian J., Stach, James E. M., Willis, Christine L., Race, Paul R.
Journal of the American Chemical Society 2016 v.138 no.19 pp. 6095-6098
X-ray diffraction, active sites, biocatalysts, catalytic activity, cycloaddition reactions
The Diels–Alder reaction, a [4 + 2] cycloaddition of a conjugated diene to a dienophile, is one of the most powerful reactions in synthetic chemistry. Biocatalysts capable of unlocking new and efficient Diels–Alder reactions would have major impact. Here we present a molecular-level description of the reaction mechanism of the spirotetronate cyclase AbyU, an enzyme shown here to be a bona fide natural Diels–Alderase. Using enzyme assays, X-ray crystal structures, and simulations of the reaction in the enzyme, we reveal how linear substrate chains are contorted within the AbyU active site to facilitate a transannular pericyclic reaction. This study provides compelling evidence for the existence of a natural enzyme evolved to catalyze a Diels–Alder reaction and shows how catalysis is achieved.