In response to the intercellular messenger ATP, P2X receptors transfer various sensory information, including pain. Here we have reconstructed the structure of the P2X2 receptor at 15 Å resolution from more than 90,000 particle images, taken with a cryo-electron microscope equipped with a helium-cooled stage. This three-dimensional depiction, presumably in a closed state, revealed an elongated vase-shaped structure 202 Å in height and 160 Å in major diameter. The extracellular and transmembrane domains present a two-layered structure, in which a sparse outer layer surrounds a pore-forming inner density. The decreased diameter of a putative ion-conducting pathway at the middle of the membrane was considered to be the narrowest part of the pore, which has been predicted from electrophysiological studies. The sparse, extended structure of the P2X2 receptor indicates a loose assembly of subunits, which could be a basis for the activation-dependent pore dilation of P2X receptors.
