Interactions among Positions in the Third and Fourth Membrane-associated Domains at the Intersubunit Interface of the N-Methyl-d-aspartate Receptor Forming Sites of Alcohol Action

Abstract

Background:The NMDA receptor is a major target of alcohol action in the brain. Results: Four pairs of residues at the M3-M4 domain intersubunit interfaces interact to regulate gating and alcohol sensitivity. Conclusion: NMDA receptors contain putative sites of alcohol action at the M3-M4 domain interfaces. Significance: Identifying molecular sites of alcohol action on its targets is essential for understanding its actions.

A Novel Alcohol-Sensitive Position in the N-Methyl-d-Aspartate Receptor GluN2A Subunit M3 Domain Regulates Agonist Affinity and Ion Channel Gating

“…Positive correlations between substituent side chain volume and ethanol sensitivity are consistent with a model in which ethanol acts by occupying a critical volume, as has been shown in other alcohol-sensitive ligand-gated ion channels Ye et al, 1998;Koltchine et al, 1999;Yamakura et al, 1999;Kash et al, 2003). The lack of such a correlation in our study may indicate that the side chain at 636 does not project into the interior of an alcohol binding site but rather forms part of the outer boundary of such a site (Ren et al, 2012). In this case, the side chain at 636 would regulate receptor function in a more complex manner depending on its interactions with other side chains in its environment.…”

“…In that study, we identified five positions in the GluN1 and GluN2A subunits that had not been previously shown to regulate ethanol sensitivity. Substitution mutations at a few of these individual positions, such as GluN2A(L824), had no effect on ethanol sensitivity by themselves (Honse et al, 2004) but influenced ethanol action only in concert with mutations at their paired position (Ren et al, 2012). In contrast, we found that tryptophan substitution at F636 in the M3 domain of GluN2A (Fig.…”

“…In contrast, we found that tryptophan substitution at F636 in the M3 domain of GluN2A (Fig. 1) showed the lowest ethanol sensitivity among identified mutants in the GluN2A subunit (Ren et al, 2012), suggesting a greater relative importance of this position in the regulation of NMDA receptor alcohol sensitivity. We therefore investigated the role of this position in the regulation of NMDA receptor ethanol sensitivity and NMDA receptor function.…”

“…The determinants of ethanol sensitivity and receptor function at each of these positions differ markedly from each other. Recently, we found four pairs of positions at the intersubunit interface in the M3 and M4 domains of the GluN1 and GluN2A subunits, including three positions identified previously (Ronald et al, 2001;Ren et al, 2003bRen et al, , 2007, that interact with each other to regulate both ethanol sensitivity and measures of receptor function such as agonist deactivation and desensitization (Ren et al, 2012). In that study, we identified five positions in the GluN1 and GluN2A subunits that had not been previously shown to regulate ethanol sensitivity.…”

“…Substitution mutations at GluN2A(F636) could also significantly alter ethanol sensitivity. Ethanol inhibition of the NMDA receptor is not determined by a single position in the membrane-associated domains, but rather the sites of ethanol action on the NMDA receptor appear to be composed of several interacting positions located in the M domains (Ren et al, 2012), each of which possess unique characteristics (Ronald et al, 2001;Ren et al, 2003bRen et al, , 2007Smothers and Woodward, 2006). For previously identified ethanol-sensitive positions in GluN2A, ethanol sensitivity was dependent on the molecular volume and hydrophilicity of the substituent at M823 (Ren et al, 2003b), was inversely dependent upon the molecular volume of the substituent at F637 (Ren et al, 2007), but was not correlated with any physicochemical measure of the substituent at A825 (Salous et al, 2009).…”