title: Disruption of agonist and ligand activity in an AMPA glutamate receptor splice-variable domain deletion mutant.
abstract: The mechanisms by which agonists and other ligands bind ligand-gated ion channels are important determinants of function in neurotransmitter receptors. The partial agonist, kainic acid (KA) activates a less desensitized, and more robust AMPA receptor (AMPAR) current than full agonists, glutamate or AMPA. Cyclothiazide (CTZ), the allosteric modulator of AMPARs, potentiates receptor currents by inhibiting receptor desensitization resulting from agonist activation. We have constructed an AMPAR GluR1 subunit deletion mutant GluR1L3T(Delta739-784) by deleting the splice-variable "flip/flop" region of the L3 domain in the wild-type receptor and compared its function to that of the wild-type GluR1 receptor and an AMPAR substitution mutant GluR1A782N. When compared to GluR1, the potency of glutamate activation of GluR1L3T was increased, in contrast to a decrease in potency of activation and reduced sensitivity to optimal concentrations of KA. Furthermore, GluR1L3T was totally insensitive to CTZ potentiation of KA and glutamate-activated currents in Xenopus laevis oocytes. The potency of glutamate and KA activation of GluR1A782N was not significantly different from that of the wild-type GluR1 receptor although the mutant receptor currents were more sensitive to CTZ potentiation than the wild-type receptor current. This result is an indication that glutamate and KA binding to the agonist (S1/S2) domain on AMPAR can be modulated by an expendable splice-variable region of the receptor. Moreover, the effect of the allosteric modulator, CTZ on agonist activation of AMPAR can also be modified by a non-conserved amino acid residue substitution within the splice-variable "flip/flop" region.
authors.affiliation: Department of Pharmacology, Howard University College of Medicine, 520 W Street N.W., Washington, DC 20059, USA.
authors.forename: Wayne D
authors.initials: WD
authors.lastname: Johnson
authors.forename: Vijaya
authors.initials: V
authors.lastname: Parandaman
authors.forename: Emmanuel S
authors.initials: ES
authors.lastname: Onaivi
authors.forename: Robert E
authors.initials: RE
authors.lastname: Taylor
authors.forename: B Emmanuel
authors.initials: BE
authors.lastname: Akinshola
mesh_terms: D000409:Alanine / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D001216:Asparagine / Q000235:genetics; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology; D007814:Larva; D007930:Leucine / Q000235:genetics; D008024:Ligands; D008564:Membrane Potentials / Q000187:drug effects* / Q000235:genetics / Q000528:radiation effects; D008845:Microinjections / Q000379:methods; D009865:Oocytes; D018408:Patch-Clamp Techniques; D017434:Protein Structure, Tertiary / Q000235:genetics; D018091:Receptors, AMPA / Q000235:genetics* / Q000378:metabolism*; D017384:Sequence Deletion / Q000235:genetics*; D013912:Threonine / Q000235:genetics; D014981:Xenopus
chemical_list: D000409:Alanine; D001216:Asparagine; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D018698:Glutamic Acid; D007930:Leucine; D008024:Ligands; D018091:Receptors, AMPA; D013912:Threonine