PT  - JOURNAL ARTICLE
AU  - Jiming Chen
AU  - Alexandra White
AU  - David C. Nelson
AU  - Diwakar Shukla
TI  - Role of substrate recognition in modulating strigolactone receptor selectivity in witchweed
AID  - 10.1101/2020.07.28.225722
DP  - 2020 Jan 01
TA  - bioRxiv
PG  - 2020.07.28.225722
4099  - http://biorxiv.org/content/early/2020/07/29/2020.07.28.225722.short
4100  - http://biorxiv.org/content/early/2020/07/29/2020.07.28.225722.full
AB  - Witchweed, or Striga hermonthica, is a parasitic weed that destroys billions of dollars worth of crops globally every year. Its germination is stimulated by strigolactones exuded by its host plants. Despite high sequence, structure, and ligand binding site conservation across different plant species, one strigolactone receptor in witchweed (Sh HTL7) uniquely exhibits a picomolar EC50 for downstream signaling. Previous biochemical and structural analyses have hypothesized that this unique ligand sensitivity can be attributed to a large binding pocket volume in Sh HTL7 resulting in enhanced ability to bind substrates. Additional structural details of the substrate binding process can help explain its role in modulating the ligand selectivity. Using long-timescale molecular dynamics simulations, we demonstrate that mutations at the entrance of the binding pocket facilitate a more direct ligand binding pathway to Sh HTL7, whereas hydrophobicity at the binding pocket entrance results in a stable “anchored” state. We also demonstrate that several residues on the D-loop of At D14 stabilize catalytically inactive conformations. Finally, we show that strigolactone selectivity is not modulated by binding pocket volume. Our results indicate that while ligand binding is not the sole modulator of strigolactone receptor selectivity, it is a significant contributing factor. These results can be used to inform the design of selective antagonists for strigolactone receptors in witchweed.Competing Interest StatementThe authors have declared no competing interest.