title: Molecular lock regulates binding of glycine to a primitive NMDA receptor.
abstract: The earliest metazoan ancestors of humans include the ctenophore Mnemiopsis leidyi The genome of this comb jelly encodes homologs of vertebrate ionotropic glutamate receptors (iGluRs) that are distantly related to glycine-activated NMDA receptors and that bind glycine with unusually high affinity. Using ligand-binding domain (LBD) mutants for electrophysiological analysis, we demonstrate that perturbing a ctenophore-specific interdomain Arg-Glu salt bridge that is notably absent from vertebrate AMPA, kainate, and NMDA iGluRs greatly increases the rate of recovery from desensitization, while biochemical analysis reveals a large decrease in affinity for glycine. X-ray crystallographic analysis details rearrangements in the binding pocket stemming from the mutations, and molecular dynamics simulations suggest that the interdomain salt bridge acts as a steric barrier regulating ligand binding and that the free energy required to access open conformations in the glycine-bound LBD is largely responsible for differences in ligand affinity among the LBD variants.
authors: Department of Biophysics and Biophysical Chemistry, The Johns Hopkins University School of Medicine, Baltimore, MD 21205.
authors: Alvin
authors: A
authors: Yu
authors: Department of Biophysics and Biophysical Chemistry, The Johns Hopkins University School of Medicine, Baltimore, MD 21205.|Laboratory of Cellular and Molecular Neurophysiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892.
authors: Robert
authors: R
authors: Alberstein
authors: Laboratory of Cellular and Molecular Neurophysiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892.
authors: Alecia
authors: A
authors: Thomas
authors: Laboratory of Cellular and Molecular Neurophysiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892.
authors: Austin
authors: A
authors: Zimmet
authors: Laboratory of Cellular and Molecular Neurophysiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892.
authors: Richard
authors: R
authors: Grey
authors: Laboratory of Cellular and Molecular Neurophysiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892 mark.mayer@nih.gov alau@jhmi.edu.
authors: Mark L
authors: ML
authors: Mayer
authors: Department of Biophysics and Biophysical Chemistry, The Johns Hopkins University School of Medicine, Baltimore, MD 21205; mark.mayer@nih.gov alau@jhmi.edu.
authors: Albert Y
authors: AY
authors: Lau
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D018360:Crystallography, X-Ray; D037302:Ctenophora / Q000378:metabolism; D004151:Dipeptides; D004594:Electrophysiology; D005998:Glycine / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D006860:Hydrogen Bonding; D008024:Ligands; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D050505:Mutant Proteins; D017354:Point Mutation; D011485:Protein Binding / Q000235:genetics; D011487:Protein Conformation; D058468:Receptors, Ionotropic Glutamate / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D004151:Dipeptides; D008024:Ligands; D050505:Mutant Proteins; D058468:Receptors, Ionotropic Glutamate; D016194:Receptors, N-Methyl-D-Aspartate; D005998:Glycine; C024362:arginine glutamate
keywords: X-ray crystallography; electrophysiology; free energy calculations; glutamate receptors; molecular dynamics simulations