P2X2 receptor subunit interfaces are missense variant hotspots, where mutations tend to increase apparent ATP affinity.

We provide the first structural mapping of the mutational distribution across the human population in a ligand-gated ion channel and show that the density of missense mutations is constrained between protein domains, indicating evolutionary selection at the domain level. Our data may indicate that, unlike other ligand-gated ion channels, P2X2 receptors have evolved an intrinsically high threshold for activation, possibly to allow for additional modulation or as a cellular protection mechanism against overstimulation.