Gating mechanisms and pharmacology of P2X receptor channels

National Institute Of Neurological Disorders And Stroke

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Abstract

1) Extracellular ATP activates a family of P2X receptor channels (P2XRs) that are widely expressed in the nervous and immune systems where they serve critical roles in nociception, sensing hypoxia, taste, synaptic homeostasis, inflammation and immunity. The available structures of P2XRs in detergents reveal their trimeric architecture and an unprecedented mechanism of channel opening wherein large crevices between subunits open within the transmembrane (TM) region. In addition, the mechanisms of agonist recognition in some P2XR subtypes and regulation of channel opening remain enigmatic. Here we investigated the mechanisms of ligand recognition and channel gating for P2X2Rs, a subtype that requires ATP4- for activation, is tightly regulated by protons and Zn2+ and for which no structures are available. We resolved structures of the human P2X2R (hP2X2R) in lipid nanodiscs in closed, open, desensitized and intermediate states, revealing that membrane lipids stabilize interactions between TM helices to maintain subunit interfaces during channel opening. The ATP binding pocket contains unique features that underlie the requirement for activation by ATP4-, in addition to binding of the large anchor-shaped antagonist suramin. Finally, we identified a regulatory nexus in the extracellular domain (ECD) of hP2X2Rs that is ideally positioned to couple ATP binding to opening of the pore and modulate channel activity by protons and Zn2+ 11-15. Taken together, these findings establish key principles of gating in P2XRs in a membrane-like environment, providing a framework for future mechanistic studies and therapeutic development.