Crystal structure of fatty acid thioesterase A bound by 129 fragments provides diverse development opportunities.

In order to alleviate the growing issue of herbicide resistance, diversification of the herbicide portfolio is necessary. A promising yet underutilized mode-of-action is the inhibition of fatty acid thioesterases (FATs), which terminate de novo fatty acid (FA) biosynthesis by releasing FAs from acyl carrier protein (ACP) cofactors. These enzymes impact plant growth and sterility by determining the amount and length of FAs present. In this study we report a crystallographic fragment screening approach for the identification of novel chemical matter targeting FATs. We have solved the crystal structure of Arabidopsis thaliana FatA to 1.5 Å and conducted a crystallographic fragment screen which identified 129 unique fragments bound in 141 different poses. Ten fragments demonstrated on-scale potency, two of these exploiting different interactions to known herbicides. Elaboration of one of the fragments resulted in an improvement of affinity from ~20 μm to ~90 nm KD. Finally, superposition of our crystal structures revealed that some fragments exploit large conformational changes in the substrate binding site. We have fully enabled FatA as a target for rapid, rational hit-to-lead development, with robust structural, biophysical and biochemical assays. We provide a set of fragment hits which represent diverse, novel scaffolds that both recapitulate interactions made by current herbicides, and also target novel regions within the active and dimer sites. Our fragments can be readily merged and allow for effective catalogue-based structure-activity relationship (SAR) exploration. Together these data will accelerate the development of novel, alternative herbicides to combat herbicide resistance.