Abstract
In organic synthesis, bifunctional chiral catalysts are an increasingly popular tool to position and stabilize a nucleophile and activate an electrophile for asymmetric addition reactions. It turns out that organic chemists were not first to employ this synthetic strategy, plants have been using an similar method for quite some time (~500 million years). By using techniques in structural biology, enzymology and NMR, we characterize a novel mechanism by which the enzyme chalcone isomerase (CHI) catalyzes oxa‐Michael cyclizations of 2′‐hydroxychalcones into flavanones; a key early step in the synthesis of flavonoid compounds in plants. The enzyme enhances these reaction rates by utilizing the guanidine of a conserved arginine in a bifunctional capacity to position the nucleophilic phenoxide and activate the electrophilic enone of the chalcone substrate. In addition, we reveal the structural and biochemical basis of an evolutionary neofunctionalization event, in which a divergent clade of CHIs unique to Legumes expanded it's substrate repertoire to include 6′‐deoxychalcone substrates. Together these results reveal the details of key evolutionary mechanistic innovations unique to this class of plant enzymes.Support or Funding InformationHHMIThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.
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