Bi-directional allosteric pathway in NMDA receptor activation and modulation

Area of Science:

• Neuroscience
• Molecular Biology
• Biophysics

Background:

• N-methyl-D-aspartate (NMDA) receptors are crucial ionotropic glutamate receptors essential for cognitive functions like learning and memory.
• The NMDA receptor's function is modulated by its subunits, particularly the GluN2 subunit, which influences receptor activation and desensitization.
• GluN2A- and GluN2D-containing NMDA receptors exhibit distinct biophysical properties, representing functional extremes.

Purpose of the Study:

• To elucidate the conformational differences underlying the functional divergence between GluN2A- and GluN2D-containing NMDA receptors.
• To investigate the allosteric communication pathways within NMDA receptors.

Main Methods:

• Utilized single-molecule fluorescence resonance energy transfer (smFRET) to probe the extracellular domains of NMDA receptor subtypes.
• Examined receptor conformations under resting and ligand-bound conditions.

Main Results:

• The conformational profile of the GluN2 amino-terminal domain (ATD) correlates with the distinct functions of GluN2A and GluN2D receptors.
• Observed inverse correlations between conformational changes in the pre-transmembrane segments and the ATD, indicating allosteric communication.
• Demonstrated that positive allosteric modulators binding to the transmembrane domain induce conformational shifts in the ATD towards an active state.

Conclusions:

• The conformational dynamics of the GluN2 ATD are critical for the functional divergence of NMDA receptor subtypes.
• Established a bidirectional allosteric pathway connecting the extracellular and transmembrane domains of NMDA receptors.
• Provided insights into the molecular mechanisms governing NMDA receptor function and modulation.