Cryo-EM structures of human P2X2/3 heteromer channel reveal the structural basis of ligand selectivity.

Abstract

P2X3 receptors are key mediators of adenosine 5'-triphosphate (ATP)-evoked cough reflexes and validated drug targets, but first-generation antagonists such as gefapixant are limited by off-target inhibition of P2X2/3 heteromers in taste pathways. Here, we report the first cryo-electron microscopy (cryo-EM) structures of the human P2X2/3 heteromer in multiple ligand-bound states. The structures resolve its debated stoichiometries (1:2 and 2:1), reveal asymmetric pore organization, and identify heteromer-specific rearrangements that modulate ATP binding and gating. Structural and functional analyses show that gefapixant binds a conserved interfacial allosteric pocket, explaining its poor selectivity and taste-related side effects, whereas the next-generation antagonist camlipixant exploits a divergent vestibular site unique to P2X3, conferring >10,000-fold selectivity and improved tolerability. These findings establish a structural framework for P2X2/3 assembly and drug recognition and provide a roadmap for rational design of selective P2X modulators with enhanced safety and efficacy.