A Mechanistic Approach\non Perception Mode of ABA Receptors\n(PYLs) to Novel Opabactin Analogues

This study explored the structural mechanisms governing\nthe binding\nof opabactin (OP) analogues <b>2</b>–<b>6</b> to\nabscisic acid (ABA) receptors by employing a combination of micro-scale\nthermophoresis (MST), phosphatase activity inhibition assays, and\nmolecular dynamics simulations. The compounds <b>3</b>–<b>6</b> selectively activated PYR1, PYL2, and PYL6, while exhibiting\nminimal activity against PYL10, thus identifying them as selective\nABA receptor agonists. Additionally, these analogues exerted a significant\ninhibitory effect on the phosphatase HAB1 upon binding to the receptors.\nThe molecular dynamics simulations further elucidated the detailed\nbinding interactions between various OP analogues and the ABA receptor\nPYR1, highlighting their role in inducing conformational changes within\nthe receptor. Specifically, the study focused on the facilitation\nof the closure of the Gate and CL1 loops and the fine-tuning of the\nLatch loop to enhance the plasticity of the binding pocket, thereby\ninfluencing receptor–ligand interactions. The investigation\nemphasized the critical role of conserved water molecules in stabilizing\nthe ligand-PYLs-PP2Cs complexes. Furthermore, free energy decomposition\ncalculations demonstrated that the ligand’s affinity was significantly\naffected by its ability to establish polar contacts between the polar\ngroups within the ligand tail and the residues at the base of the\nbinding pocket. This research lays a robust foundation for the development\nof novel ABA functional analogues with improved activity.