title: A Molecular Determinant of Subtype-Specific Desensitization in Ionotropic Glutamate Receptors.
abstract: AMPA and NMDA receptors are glutamate-gated ion channels that mediate fast excitatory synaptic transmission throughout the nervous system. In the continual presence of glutamate, AMPA and NMDA receptors containing the GluN2A or GluN2B subunit enter into a nonconducting, desensitized state that can impact synaptic responses and glutamate-mediated excitotoxicity. The process of desensitization is dramatically different between subtypes, but the basis for these differences is unknown. We generated an extensive sequence alignment of ionotropic glutamate receptors (iGluRs) from diverse animal phyla and identified a highly conserved motif, which we termed the "hydrophobic box," located at the extracellular interface of transmembrane helices. A single position in the hydrophobic box differed between mammalian AMPA and NMDA receptors. Surprisingly, we find that an NMDAR-to-AMPAR exchange mutation at this position in the rat GluN2A or GluN2B subunit had a dramatic and highly specific effect on NMDAR desensitization, making it AMPAR-like. In contrast, a reverse exchange mutation in AMPARs had minimal effects on desensitization. These experiments highlight differences in desensitization between iGluR subtypes and the highly specific contribution of the GluN2 subunit to this process.
  
  
  CONCLUSIONS
  Rapid communication between cells in the nervous system depends on ion channels that are directly activated by neurotransmitter molecules. Here, we studied ionotropic glutamate receptors (iGluRs), which are ion channels activated by the neurotransmitter glutamate. By comparing the sequences of a vast number of iGluR proteins from diverse animal species, assisted by available structural information, we identified a highly conserved motif. We showed that a single amino acid difference in this motif between mammalian iGluR subtypes has dramatic effects on receptor function. These results have implications in both the evolution of synaptic function, as well as the role of iGluRs in health and disease.
authors.affiliation: Departments of Neurobiology & Behavior and.
authors.forename: Matthew
authors.identifier: http://orcid.org/0000-0002-9832-0138
authors.initials: M
authors.lastname: Alsaloum
authors.affiliation: Graduate Program in Neuroscience, Medical Scientist Training Program.
authors.forename: Rashek
authors.initials: R
authors.lastname: Kazi
authors.affiliation: Graduate Program in Neuroscience.
authors.forename: Quan
authors.initials: Q
authors.lastname: Gan
authors.affiliation: Medical Scientist Training Program.
authors.forename: Johansen
authors.initials: J
authors.lastname: Amin
authors.affiliation: Departments of Neurobiology & Behavior and Biochemistry & Cell Biology, and Center for Nervous System Disorders, Stony Brook University, Stony Brook, New York 11794-5230 lonnie.wollmuth@stonybrook.edu.
authors.forename: Lonnie P
authors.identifier: http://orcid.org/0000-0002-8179-1259
authors.initials: LP
authors.lastname: Wollmuth
mesh_terms: D000818:Animals; D055592:Biophysical Phenomena; D004558:Electric Stimulation; D018698:Glutamic Acid / Q000494:pharmacology; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D016296:Mutagenesis / Q000235:genetics*; D009154:Mutation / Q000235:genetics; D018408:Patch-Clamp Techniques; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D051381:Rats; D058468:Receptors, Ionotropic Glutamate / Q000737:chemistry / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D014162:Transfection
chemical_list: D021122:Protein Subunits; D058468:Receptors, Ionotropic Glutamate; D049452:Green Fluorescent Proteins; D018698:Glutamic Acid
keywords: AMPA receptors; NMDA receptors; gating; sequence alignments; structures