title: Mechanism of Cl- selection by a glutamate-gated chloride (GluCl) receptor revealed through mutations in the selectivity filter.
abstract: To learn about the mechanism of ion charge selectivity by invertebrate glutamate-gated chloride (GluCl) channels, we swapped segments between the GluClbeta receptor of Caenorhabditis elegans and the vertebrate cationic alpha7-acetylcholine receptor and monitored anionic/cationic permeability ratios. Complete conversion of the ion charge selectivity in a set of receptor microchimeras indicates that the selectivity filter of the GluClbeta receptor is created by a sequence connecting the first with the second transmembrane segments. A single substitution of a negatively charged residue within this sequence converted the selectivity of the GluClbeta receptor's pore from anionic to cationic. Unexpectedly, elimination of the charge of each basic residue of the selectivity filter, one at a time or concomitantly, moderately reduced the P(Cl)/P(Na) ratios, but the GluClbeta receptor's mutants retained high capacity to select Cl(-) over Na(+). These results indicate that, unlike the proposed case of anionic Gly- and gamma-aminobutyric acid-gated ion channels, positively charged residues do not play the key role in the selection of ionic charge by the GluClbeta receptor. Taken together with measurements of the effective open pore diameter and with structural modeling, the study presented here collectively indicates that in the most constricted part of the open GluClbeta receptor's channel, Cl(-) interacts with backbone amides, where it undergoes partial dehydration necessary for traversing the pore.
authors.affiliation: Unit of Receptors and Cognition, URA 2182 CNRS, Pasteur Institute, 25 rue du Docteur Roux, 75724 Paris Cedex 15, France.
authors.forename: Morten
authors.initials: M
authors.lastname: Sunesen
authors.forename: Lia Prado
authors.initials: LP
authors.lastname: de Carvalho
authors.forename: Virginie
authors.initials: V
authors.lastname: Dufresne
authors.forename: Regis
authors.initials: R
authors.lastname: Grailhe
authors.forename: Nathalie
authors.initials: N
authors.lastname: Savatier-Duclert
authors.forename: Gilad
authors.initials: G
authors.lastname: Gibor
authors.forename: Asher
authors.initials: A
authors.lastname: Peretz
authors.forename: Bernard
authors.initials: B
authors.lastname: Attali
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Changeux
authors.forename: Yoav
authors.initials: Y
authors.lastname: Paas
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017173:Caenorhabditis elegans; D018118:Chloride Channels / Q000737:chemistry* / Q000235:genetics*; D002712:Chlorides / Q000737:chemistry*; D004594:Electrophysiology; D005971:Glutamates / Q000737:chemistry*; D006801:Humans; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid
chemical_list: D018118:Chloride Channels; D002712:Chlorides; D005971:Glutamates; D011993:Recombinant Fusion Proteins; C109777:glutamate-gated chloride channels