The NMDA receptor intracellular C-terminal domains reciprocally interact with allosteric modulators

Abstract

N-Methyl-D-aspartate receptors (NMDARs) have multiple prominent roles in CNS function but their excessive or insufficient activity contributes to neuropathological/psychiatric disorders. Consequently, a variety of positive and negative allosteric modulators (PAMs and NAMs, respectively) have recently been developed. Although these modulators bind to extracellular domains, in the present report we find that the NMDAR's intracellular C-terminal domains (CTDs) significantly influence PAM/NAM activity. GluN2 CTD deletion robustly affected NAM and PAM activity with both enhancing and inhibiting effects that were compound-specific and NMDAR subunit-specific. In three cases, individual PAMs became NAMs at specific GluN2-truncated receptors. In contrast to GluN2, GluN1 CTD removal only reduced PAM activity of UBP684 and CIQ, and did not affect NAM activity. Consistent with these findings, agents altering phosphorylation state or intracellular calcium levels displayed receptor-specific and compound-specific effects on PAM activity. It is possible that the GluN2's M4 domain transmits intracellular modulatory signals from the CTD to the M1/M4 channel gating machinery and that this site is a point of convergence in the direct or indirect actions of several PAMs/NAMs thus rendering them sensitive to CTD status. Thus, allosteric modulators are likely to have a marked and varied sensitivity to post-translational modifications, protein-protein associations, and intracellular ions. The interaction between PAM activity and NMDAR CTDs appears reciprocal. GluN1 CTD-deletion eliminated UBP684, but not pregnenolone sulfate (PS), PAM activity. And, in the absence of agonists, UBP684, but not PS, was able to promote movement of fluorescently-tagged GluN1-CTDs. Thus, it may be possible to pharmacologically target NMDAR metabotropic activity in the absence of channel activation.

The C‐terminal domains of the NMDA receptor: How intrinsically disordered tails affect signalling, plasticity and disease

“…respectively, which indicates that the phosphorylation state of the CTD also regulates allosteric modulation (Sapkota et al, 2019). Tyrosine phosphorylation regulates GluN2Acontaining receptors as phosphorylation at Y1325 and Y1387 potentiates GluN2A-mediated currents (Taniguchi et al, 2009;Zheng, Gingrich, Traynelis, & Conn, 1998).…”

Datumetine Preferentially Upregulates N-methyl-D-aspartate Receptor Signalling Pathways in Different Brain Regions of Mice

“…Glutamate transmission plays a significant role in hippocampal functions (Vásquez et al, 2014). Blocking NMDAR might have caused increased receptor sensitivity thereby responsible for this observed effect (Kennedy, 2010;Sapkota et al, 2019). The different observation was seen in the cerebellum as Datumetine animals showed an increased level of CamKIIα while MK-801 pre-treatment was able to reverse this effect.…”

“…N-methyl-D-aspartate receptor (NMDAR) is an ionotropic glutamate receptor expressed ubiquitously in the brain (Kennedy, 2010;Sapkota et al, 2019;Sattler et al, 2000). It belongs to the ionotropic class of glutamate receptors (Montes de Oca Balderas, 2018;Reiner & Levitz, 2018).…”

“…It belongs to the ionotropic class of glutamate receptors (Montes de Oca Balderas, 2018;Reiner & Levitz, 2018). NMDAR activation by glutamate leads to an influx of Ca 2+ which activates a diverse range of intracellular signalling cascade (Cho et al, 2012;Kennedy, 2010;Montes de Oca Balderas, 2018;Sapkota et al, 2019). This is why NMDAR is regarded as an electrochemical coupling (S. Zhu et al, 2016).…”

Regulation of NMDA Receptor Subtypes in Pain Processing Neurons within Lamina I of the Spinal Cord

“…Moreover, for the remaining GluN2B/D NMDARs, binding of DQP-1105 or Ro25-6981 to the extracellular domain of GluN2D or GluN2B may interfere with intracellular phosphorylation of triheteromeric GluN2B/D NMDARs by Fyn, preventing the potentiation of residual currents in the presence of either antagonist. Proof of interaction between intracellular and extracellular modulators of NMDARs has recently been shown by cleaving the intracellular domain of GluN2A-D subunits, resulting in decreased potentiation by positive allosteric modulators of GluN2 subunits (Sapkota et al, 2019). It was also shown that cleaving the intracellular domain of the GluN1 subunit affected potentiation by positive allosteric modulators of GluN2 subunits, suggesting that the intracellular domain of one subunit in a tetrameric NMDAR can interact with the extracellular domain of another subunit in the tetrameric assembly.…”