title: The N-terminal domain of the GluN3A subunit determines the efficacy of glycine-activated NMDA receptors.
abstract: N-methyl-d-aspartate (NMDA) receptors composed of glycine-binding GluN1 and GluN3 subunits function as excitatory glycine receptors that respond to agonist application only with a very low efficacy. Binding of glycine to the high-affinity GluN3 subunits triggers channel opening, whereas glycine binding to the low-affinity GluN1 subunits causes an auto-inhibition of the maximal glycine-inducible receptor current (Imax). Hence, competitive antagonists of the GluN1 subunit strongly potentiate glycine responses of wild type (wt) GluN1/GluN3 receptors. Here, we show that co-expression of N-terminal domain (NTD) deleted GluN1 (GluN1(ΔNTD)) and GluN3 (GluN3(ΔNTD)) subunits in Xenopus oocytes generates GluN1/GluN3 receptors with a large increase in the glycine-inducible Imax accompanied by a strongly impaired GluN1 antagonist-mediated potentiation. Affinity purification after metabolic or surface labeling revealed no differences in subunit stoichiometry and surface expression between wt GluN1/GluN3A and mutant GluN1(ΔNTD)/GluN3A(ΔNTD) receptors, indicating a specific effect of NTD deletions on the efficacy of receptor opening. Notably, GluN1/GluN3A(ΔNTD) receptors showed a similar increase in Imax and a greatly reduced GluN1 antagonist-mediated current potentiation as GluN1(ΔNTD)/GluN3A(ΔNTD) receptors, whereas the glycine-induced currents of GluN1(ΔNTD)/GluN3A receptors resembled those of wt GluN1/GluN3A receptors. Furthermore, oxidative crosslinking of the homophilic GluN3A NTD intersubunit interface in mutant GluN1/GluN3A(R319C) receptors caused both a decrease in the glycine-induced Imax concomitantly with a marked increase in GluN1 antagonist-mediated current potentiation, whilst mutations within the intrasubunit region linking the GluN3A NTD to the ligand binding domain had opposite effects. Together these results show that the GluN3A NTD constitutes a crucial regulatory determinant of GluN1/GluN3A receptor function.
authors.affiliation: Department of Neurochemistry, Max-Planck-Institute for Brain Research, Deutschordenstrasse 46, 60528 Frankfurt am Main, Germany; Department of Neurophysiology and Neurosensory Systems, Technische Universität Darmstadt, Schnittspahnstrasse 3, 64287 Darmstadt, Germany.
authors.forename: Ivana
authors.initials: I
authors.lastname: Mesic
authors.affiliation: Department of Neurochemistry, Max-Planck-Institute for Brain Research, Deutschordenstrasse 46, 60528 Frankfurt am Main, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Madry
authors.affiliation: Department of Neurophysiology and Neurosensory Systems, Technische Universität Darmstadt, Schnittspahnstrasse 3, 64287 Darmstadt, Germany.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Geider
authors.affiliation: Department of Neurophysiology and Neurosensory Systems, Technische Universität Darmstadt, Schnittspahnstrasse 3, 64287 Darmstadt, Germany.
authors.forename: Max
authors.initials: M
authors.lastname: Bernhard
authors.affiliation: Department of Neurochemistry, Max-Planck-Institute for Brain Research, Deutschordenstrasse 46, 60528 Frankfurt am Main, Germany; Max-Planck-Institute for Medical Research, Jahnstrasse 29, 69120 Heidelberg, Germany.
authors.forename: Heinrich
authors.initials: H
authors.lastname: Betz
authors.affiliation: Department of Neurochemistry, Max-Planck-Institute for Brain Research, Deutschordenstrasse 46, 60528 Frankfurt am Main, Germany; Department of Neurophysiology and Neurosensory Systems, Technische Universität Darmstadt, Schnittspahnstrasse 3, 64287 Darmstadt, Germany. Electronic address: laube@bio.tu-darmstadt.de.
authors.forename: Bodo
authors.initials: B
authors.lastname: Laube
mesh_terms: D000818:Animals; D001665:Binding Sites; D005998:Glycine / Q000494:pharmacology / Q000502:physiology*; D017434:Protein Structure, Tertiary; D018009:Receptors, Glycine / Q000819:agonists / Q000737:chemistry / Q000502:physiology*; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology*; D014982:Xenopus laevis
chemical_list: C464437:NR3A NMDA receptor; D018009:Receptors, Glycine; D016194:Receptors, N-Methyl-D-Aspartate; D005998:Glycine
keywords: Excitatory glycine receptor; N-methyl-d-aspartate receptor; N-terminal domain; Receptor structure-function; Structural model; Xenopus