title: A conserved mechanism for gating in an ionotropic glutamate receptor.
abstract: Ionotropic glutamate receptor (iGluR) channels control synaptic activity. The crystallographic structure of GluA2, the prototypical iGluR, reveals a clamshell-like ligand-binding domain (LBD) that closes in the presence of glutamate to open a gate on the pore lining α-helix. How LBD closure leads to gate opening remains unclear. Here, we show that bending the pore helix at a highly conserved alanine residue (Ala-621) below the gate is responsible for channel opening. Substituting Ala-621 with the smaller more flexible glycine resulted in a basally active, nondesensitizing channel with ∼39-fold increase in glutamate potency without affecting surface expression or binding. On GluA2(A621G), the partial agonist kainate showed efficacy similar to a full agonist, and competitive antagonists CNQX and DNQX acted as a partial agonists. Met-629 in GluA2 sits above the gate and is critical in transmitting LBD closure to the gate. Substituting Met-629 with the flexible glycine resulted in reduced channel activity and glutamate potency. The pore regions in potassium channels are structurally similar to iGluRs. Whereas potassium channels typically use glycines as a hinge for gating, iGluRs use the less flexible alanine as a hinge at a similar position to maintain low basal activity allowing for ligand-mediated gating.
authors.affiliation: Weis Center for Research, Geisinger Clinic, Danville, Pennsylvania 17822-2621, USA.
authors.forename: Bryn S
authors.initials: BS
authors.lastname: Moore
authors.forename: Uyenlinh L
authors.initials: UL
authors.lastname: Mirshahi
authors.forename: Tonya L
authors.initials: TL
authors.lastname: Ebersole
authors.forename: Tooraj
authors.initials: T
authors.lastname: Mirshahi
mesh_terms: D000409:Alanine / Q000737:chemistry*; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D005998:Glycine / Q000737:chemistry; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating; D007608:Kainic Acid / Q000737:chemistry; D008024:Ligands; D009474:Neurons / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000737:chemistry; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D018091:Receptors, AMPA / Q000737:chemistry*; D017470:Receptors, Glutamate / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry; D014982:Xenopus laevis
chemical_list: D008024:Ligands; D015221:Potassium Channels; D018091:Receptors, AMPA; D017470:Receptors, Glutamate; D011994:Recombinant Proteins; D000409:Alanine; C104722:glutamate receptor ionotropic, AMPA 2; D007608:Kainic Acid; D005998:Glycine
keywords: Desensitization; Gating; Glutamate; Glutamate Receptors Ionotropic (AMPA, NMDA); Ion Channels; Kainate; Pharmacology