title: Disruption of a putative intersubunit electrostatic bond enhances agonist efficacy at the human α1 glycine receptor.
abstract: Partial agonists have lower efficacies than compounds considered 'full agonists', eliciting submaximal responses even at saturating concentrations. Taurine is a partial agonist at the glycine receptor (GlyR), a member of the cys-loop ligand-gated ion channel superfamily. The molecular mechanisms responsible for agonism are not fully understood but evidence suggests that efficacy at these receptors is determined by conformational changes that occur early in the process of receptor activation. We previously identified a residue located near the human α1 glycine binding site (aspartate-97; D97) that, when mutated to arginine (D97R), results in GlyR channels opening spontaneously with a high open probability, mimicking the effects of saturating glycine concentrations on wildtype GlyR. This D97 residue is hypothesized to form an electrostatic interaction with arginine-119 on an adjacent subunit, stabilizing the channel in a shut state. Here we demonstrate that the disruption of this putative bond increases the efficacy of partial agonists including taurine, as well as two other β-amino acid partial agonists, β-aminobutyric acid (β-ABA) and β-aminoisobutyric acid (β-AIBA). Even the subtle charge-conserving mutation of D97 to glutamate (D97E) markedly affects partial agonist efficacy. Mutation to the neutral alanine residue in the D97A mutant mimics the effects seen with D97R, indicating that charge repulsion does not significantly affect these findings. Our findings suggest that the determination of efficacy following ligand binding to the glycine receptor may involve the disruption of an intersubunit electrostatic interaction occurring near the agonist binding site.
authors.affiliation: Institute for Neuroscience, University of Texas at Austin, Austin, TX 78712, United States.
authors.forename: Brian T
authors.initials: BT
authors.lastname: Welsh
authors.affiliation: Waggoner Center for Alcohol & Addiction Research, Austin, TX 78712, United States.
authors.forename: Jelena
authors.initials: J
authors.lastname: Todorovic
authors.affiliation: Institute for Neuroscience, University of Texas at Austin, Austin, TX 78712, United States.
authors.forename: Dean
authors.initials: D
authors.lastname: Kirson
authors.affiliation: Waggoner Center for Alcohol & Addiction Research, Austin, TX 78712, United States.
authors.forename: Hunter M
authors.initials: HM
authors.lastname: Allen
authors.affiliation: Institute for Neuroscience, University of Texas at Austin, Austin, TX 78712, United States.
authors.forename: Michelle D
authors.initials: MD
authors.lastname: Bayly
authors.affiliation: Department of Neuroscience, University of Texas at Austin, Austin, TX 78712, United States; Division of Pharmacology and Toxicology, University of Texas at Austin, Austin, TX 78712, United States; Waggoner Center for Alcohol & Addiction Research, Austin, TX 78712, United States; Institute for Neuroscience, University of Texas at Austin, Austin, TX 78712, United States; Institute for Cell & Molecular Biology, University of Texas at Austin, Austin, TX 78712, United States. Electronic address: mihic@austin.utexas.edu.
authors.forename: S John
authors.initials: SJ
authors.lastname: Mihic
mesh_terms: D000595:Amino Acid Sequence; D000613:Aminobutyrates / Q000494:pharmacology; D000621:Aminoisobutyric Acids / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites / Q000235:genetics / Q000502:physiology; D006801:Humans; D008024:Ligands; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009154:Mutation; D018377:Neurotransmitter Agents / Q000494:pharmacology; D009865:Oocytes; D018408:Patch-Clamp Techniques; D018009:Receptors, Glycine / Q000819:agonists* / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D055672:Static Electricity; D013654:Taurine / Q000737:chemistry / Q000494:pharmacology; D014982:Xenopus laevis
chemical_list: D000613:Aminobutyrates; D000621:Aminoisobutyric Acids; D008024:Ligands; D018377:Neurotransmitter Agents; D018009:Receptors, Glycine; D013654:Taurine; C047667:3-aminobutyric acid; C033435:3-aminoisobutyric acid
keywords: Efficacy; Electrophysiology; Glycine receptor; Partial agonist; Single channel; Taurine