Structural insights into the allosteric inhibition of P2X4 receptors

Abstract

P2X receptors are ATP-activated cation channels involved in a variety of physiological functions. Among the seven subtypes of P2X receptors, the P2X4 subtype plays important roles in both the immune system and the central nervous system, particularly in neuropathic pain. Therefore, P2X4 receptors are of increasing interest as potential drug targets, and several P2X4 subtype-specific inhibitors have been developed. However, the mechanism of allosteric inhibition of P2X4 receptors remains largely unclear due to the lack of structural information. Here, we report the cryo-EM structures of the zebrafish P2X4 receptor in complex with two P2X4 subtype-specific antagonists, BX430 and BAY-1797. Both antagonists bind to the same allosteric site located at the subunit interface at the top of the extracellular domain. Structure-based mutational analysis by electrophysiology identified the important residues for the allosteric inhibition of both zebrafish and human P2X4 receptors. Interestingly, in the previously reported apo structure, the binding pocket is closed and too narrow to accommodate allosteric modulators. Structural comparison revealed the ligand-dependent structural rearrangement of the binding pocket to stabilize the binding of allosteric modulators, which in turn would prevent the structural changes of the extracellular domain associated with channel activation. Furthermore, comparison with the previously reported P2X structures of other subtypes provided mechanistic insights into subtype-specific allosteric inhibition. Overall, the present work provides structural insights into the allosteric inhibition mechanism of P2X4 receptors, facilitating the design and optimization of specific modulators for P2X4 receptors.