A Mechanistic Approach on Perception Mode of ABA Receptors (PYLs) to Novel Opabactin Analogues

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