P2X receptors (P2XRs) are a family of ATP-gated ion channels comprising homomeric and heteromeric trimers of seven subunits (P2X ₁ - P2X ₇ ) that confer different rates of desensitization. The helical recoil model of P2XR desensitization proposes the stability of the cytoplasmic cap sets the rate of desensitization, but timing of its formation is unclear for slow-desensitizing P2XRs. We report cryo-EM structures of full-length, wild-type human P2X ₄ receptor in apo, antagonist-bound, and desensitized states. Because the apo and antagonist-bound structures of this slow-desensitizing P2XR include an intact cytoplasmic cap while the desensitized state structure does not, the cytoplasmic cap forms before agonist binding. Furthermore, structural and functional data suggests the cytoplasmic cap is stabilized by lipids to slow desensitization and that P2X ₄ is further modified by glycosylation and palmitoylation. Finally, our antagonist-bound inhibited state structure reveals features specific to the allosteric ligand-binding pocket in human receptors that empower the development of small-molecule modulators.

P2X受体（P2XR）是一组由七种亚基（P2X₁-P2X₇）组成的ATP门控离子通道家族，这些亚基可以形成同三聚体和异三聚体，并赋予不同的脱敏感速率。 P2XR脱敏的螺旋回缩模型提出细胞质帽的稳定性决定了脱敏速率，但对于慢脱敏型P2XR来说，其形成的时机尚不清楚。我们报告了全长野生型人P2X₄受体在无配基状态、拮抗剂结合状态和脱敏状态下的冷冻电子显微镜（cryo-EM）结构。由于这种慢脱敏型P2XR的无配基和拮抗剂结合结构包含完整的细胞质帽，而脱敏状态下没有，则表明细胞质帽是在激动剂结合之前形成的。此外，结构和功能数据表明，细胞质帽通过脂质稳定来减缓脱敏过程，并且P2X₄受体还被糖基化和棕榈酰化修饰。最后，我们的拮抗剂结合抑制状态结构揭示了人类受体中别构配体结合口袋的特异性特征，这有助于小分子调节剂的发展。