XB-IMG-137673
Xenbase Image ID: 137673
|
Figure 2. Structural and functional consequences of missense mutations in GRIN2B. (A) Topology model of an NR1 and an NR2B subunit. Positions of the alterations p.Arg540His, p.Asn615Ile and p.Val618Gly are indicated by asterisks in the NR2 subunit consisting of an amino-terminal domain (ATD), the ligand-binding domain (LBD) including the S1 and S2 peptide segments, 3 transmembrane segments (M1, M2, and M3), a re-entrant pore loop (P), and an intracellular carboxy-terminal domain (CTD). Residue Arg540 lies within the glutamate-binding
domain, and Asn615 and Val618 in the ion channel pore. N = NH2-terminus; C= COOH-terminus. (B) Model of the transmembrane arrangement of the N-methyl-D-aspartate (NMDA) receptor composed of NR1 (green) and NR2B (cyan) subunits (top view). The arrow highlights the side chains of p.Asn615Ile and p.Val618Gly in the pore-forming region. (C) Gradual loss of Mg2+ inhibition of NR1-NR2B wild-type and
NR1-NR2B mutant receptor currents at −70mV. Respective sample traces of NR1-NR2B and NR1-NR2BAsn615Ile are shown above with inhibition of receptor currents by 1mM Mg2+ of NR1-NR2B (96 ± 0.9%, n=4) and mutant NR1-NR2BAsn615Ile (14 ± 7.2%, p < 0.0001, n
= 3), NR1-NR2BVal618Gly (48 ± 6.5%, p = 0.0003, n = 3), and NR1-NR2BArg540His (81 ± 3.2%, p = 0.005, n = 5) receptors. (D) Effect on Ca2+ permeability of NR1-NR2B wild-type and NR1-NR2B mutant receptor currents. Current–voltage relationships of NR1-NR2B receptors in the absence of Mg2+ in Na+-free extracellular solution reveal significant differences in the reversal potential (indicated by arrows) of NR1-NR2B (−31 ± 1.7mV, n = 4, black triangles) and mutant NR1-NR2BAsn615Ile (−1.0 ± 6.8mV,p = 0.004, n = 3, red squares),
NR1-NR2BVal618Gly (−5.4 ± 3.7mV, p < 0.001, n = 3, green squares), and NR1-NR2BArg540His (−9.4 ± 6.5mV, p = 0.013, n = 3, blue squares) receptor currents. (NMDG-Cl, N-methyl-D-glucamine chloride) Calculation of the relative divalent to monovalent cation permeability PCa/PNa by the Goldman–Hodgkin–Katz voltage equation revealed a >3-fold increase in Ca2+ permeability of the mutant NMDA receptors
(PCa/PNa for NR1-NR2B = 0.86; NR1-NR2BAsn615Ile = 5.22; NR2BVal618Gly = 3.12; and NR2BArg540His = 3.23). Image published in: Lemke JR et al. (2014) © 2014 The Authors. This image is reproduced with permission of the journal and the copyright holder. This is an open-access article distributed under the terms of the Creative Commons Attribution license Larger Image Printer Friendly View |