Article

Conserved Structural and Functional Control of N-Methyl-D-aspartate Receptor Gating by Transmembrane Domain M3

Emory University, Atlanta, Georgia, United States
Journal of Biological Chemistry (Impact Factor: 4.57). 09/2005; 280(33):29708-16. DOI: 10.1074/jbc.M414215200
Source: PubMed

ABSTRACT The molecular events controlling glutamate receptor ion channel gating are complex. The movement of transmembrane domain M3 within N-methyl-d-aspartate (NMDA) receptor subunits has been suggested to be one structural determinant linking agonist binding to channel gating. Here we report that covalent modification of NR1-A652C or the analogous mutation in NR2A, -2B, -2C, or -2D by methanethiosulfonate ethylammonium (MT-SEA) occurs only in the presence of glutamate and glycine, and that modification potentiates recombinant NMDA receptor currents. The modified channels remain open even after removing glutamate and glycine from the external solution. The degree of potentiation depends on the identity of the NR2 subunit (NR2A < NR2B < NR2C,D) inversely correlating with previous measurements of channel open probability. MTSEA-induced modification of channels is associated with increased glutamate potency, increased mean single-channel open time, and slightly decreased channel conductance. Modified channels are insensitive to the competitive antagonists D-2-amino-5-phosphonovaleric acid (APV) and 7-Cl-kynurenic acid, as well as allosteric modulators of gating (extracellular protons and Zn(2+)). However, channels remain fully sensitive to Mg(2+) blockade and partially sensitive to pore block by (+)MK-801, (-)MK-801, ketamine, memantine, amantadine, and dextrorphan. The partial sensitivity to (+)MK-801 may reflect its ability to stimulate agonist unbinding from MT-SEA-modified receptors. In summary, these data suggest that the SYTANLAAF motif within M3 is a conserved and critical determinant of channel gating in all NMDA receptors.

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    • "The reduced effect of allosteric modulators on A7-modified receptors is thought to reflect an increase in open probability that occurs after modification of the A7 residue. In MTS-treated A7C receptors, open probability is essentially at its maximum and thus agents that slow channel opening such as protons and zinc have limited opportunity to act (Yuan et al., 2005). A similar effect could explain the reduced effect of ethanol on these channels because Wright et al. (1996) showed that although 200 mM ethanol reduced mean open time and frequency of bursts, it did not introduce new closed times. "
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    • "In addition, a DRPEER motif in NR1 (Watanabe et al., 2002), a tryptophan residue in the M2 regions of NR2 subunits (Williams et al., 1998) and the common SYTANLAAF motif in TM3 (Yuan et al., 2005; Wada et al., 2006) affect the Mg 2+ block. Comparing the sequences of NR1, NR2 and NR3 subunits reveals a remarkable conservation of these regions, although especially within the QRN site and the SYTANLAAF motif several exchanges between NR1, NR2 and NR3 subunits are found. "
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    • "Previous studies have suggested that the M3 segment functions as a transduction element, coupling ligand binding to channel opening (Jones et al., 2002; Yuan et al., 2005). M3 contains the highly conserved SYTANLAAF motif, and many cysteine mutations in this region exhibit state-dependent accessibility, implying that M3 movement occurs in response to activation. "
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