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Intermediate closed state for glycine receptor function revealed by cysteine cross-linking

Abstract : Pentameric ligand-gated ion channels (pLGICs) mediate signal transmission by coupling the binding of extracellular ligands to the opening of their ion channel. Agonist binding elicits activation and desensitization of pLGICs, through several conformational states, that are, thus far, incompletely characterized at the structural level. We previously reported for GLIC, a prokaryotic pLGIC, that cross-linking of a pair of cysteines at both sides of the extracellular and transmembrane domain interface stabilizes a locally closed (LC) X-ray structure. Here, we introduced the homologous pair of cysteines on the human α1 glycine receptor. We show by electrophysiology that cysteine cross-linking produces a gain-of-function phenotype characterized by concomitant constitutive openings, increased agonist potency, and equalization of efficacies of full and partial agonists. However, it also produces a reduction of maximal currents at saturating agonist concentrations without change of the unitary channel conductance, an effect reversed by the positive allosteric modulator propofol. The cross-linking thus favors a unique closed state distinct from the resting and longest-lived desensitized states. Fitting the data according to a three-state allosteric model suggests that it could correspond to a LC conformation. Its plausible assignment to a gating intermediate or a fast-desensitized state is discussed. Overall, our data show that relative movement of two loops at the extracellular-transmembrane interface accompanies orthosteric agonist-mediated gating.
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Submitted on : Friday, March 2, 2018 - 1:47:41 PM
Last modification on : Wednesday, October 14, 2020 - 4:09:14 AM

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Marie Prevost, Gustavo Moraga-Cid, Catherine van Renterghem, Stuart Edelstein, Jean-Pierre Changeux, et al.. Intermediate closed state for glycine receptor function revealed by cysteine cross-linking. Proceedings of the National Academy of Sciences of the United States of America , National Academy of Sciences, 2013, 110 (42), pp.17113 - 17118. ⟨10.1073/pnas.1317009110⟩. ⟨pasteur-01721683⟩

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