Subtype-specific structural features of the hearing loss–associated human P2X2 receptor
Franka G. Westermann, Adam Oken, Philip K. E. Granith, Parthiban Marimuthu, Christa E. Müller, Steven Mansoor
Abstract
The P2X2 receptor (P2X2R) is a slowly desensitizing adenosine triphosphate (ATP)-gated ion channel that is highly expressed in the cochlea. When mutated, the P2X2R exacerbates age- and noise-related hearing loss, but selective modulators of the receptor are lacking, and the molecular basis of activation and desensitization remains poorly understood. Here, we determine high-resolution cryoelectron microscopy structures of the full-length wild-type human P2X2R in an apo closed state and two distinct ATP-bound desensitized states. In the apo closed state structure, we observe features unique to the P2X2R and locate disease mutations within or near the transmembrane domain. In addition, our ATP-bound structures show how free anionic ATP forms subtype-specific interactions with the orthosteric binding site. We identify and characterize two different ATP-bound desensitized state structures, one similar to published models for other P2XR subtypes, and a second alternate conformation not previously observed. A loop adjacent to the orthosteric binding site between these two ATP-bound desensitized state structures undergoes significant conformational changes. These movements are supported by multireplicate, microsecond-scale molecular dynamics simulation studies and suggest a path by which ATP could enter or leave the orthosteric pocket. Together, our results provide structural insights into the P2X2R, facilitating structure-based drug development for this therapeutically important target.