Uncommon Features Of A Novel Gamma-Proteobacterial Pentameric Ligand-Gated Ion Channel Revealed By Its Crystal Structure

Pentameric ligand-gated ion channels (pLGICs) control synaptic neurotransmission in higher eukaryotes via an allosteric mechanism, where agonist binding in the extra-cellular domain triggers the opening of an ion-conducting pore in the transmembrane domain. Here we present the x-ray structure at 2.6 A resolution of a novel bacterial homologue bound to an agonist, an amino acid analogue, in an apparently open conformation. This new structure presents unique features compared to the other pLGICs structures described to date: the presence of a constriction ring formed by 5 arginines that partially obstruct the vestibule; and an open channel pore with an extra large diameter.