Biophysical Society Thematic Meeting | Tutzing 2026

Single-Molecule FRET: The Next 30 Years

Poster Abstracts

8-POS Board 4 CHARACTERIZATION OF THE CONFORMATIONAL LANDSCAPE OF NONCANONICAL NMDA RECEPTORS VIA SMFRET Olivia Brado 1 ; Ehud Isacoff 2,3,4 ; 1 University of California, Berkeley, Biophysics Graduate Group, Berkeley, CA, USA 2 University of California, Berkeley, Department of Molecular & Cell Biology, Berkeley, CA, USA 3 Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, CA, USA 4 University of California, Berkeley, Department of Neuroscience, Berkeley, CA, USA N-methyl-D-aspartate receptors (NMDARs) are ionotropic glutamate receptors found at excitatory synapses. All NMDARs are tetramers with two obligatory glycine-binding N1 subunits and either two glutamate-binding N2 subunits, forming a “classical” excitatory glutamate receptor, or two glycine-binding N3 subunits, forming a "noncanonical" excitatory glycine receptor. Classical NMDARs have long been of particular interest due to their established role in synaptic plasticity and memory, and association with psychiatric disorders. In recent years, there has been increasing evidence of the importance of noncanonical NMDARs, which have been implicated in dendritic spine pruning, regulating the fear and stress response, and the motor deficits associated with Huntington’s Disease. Despite this, little is known about the structure and dynamics of these noncanonical NMDARs. While “classical” NMDARs are activated by both glycine in N1 and glutamate in N2, "noncanonical" NMDARs are activated by glycine in N3 but inhibited by glycine in N1. Only a handful of structures have been published of the GluN3A receptor, and most include mutations and C-terminal deletion that affect functionality. Using smFRET, we are studying the wildtype, full length receptor. We find that the N1 amino terminal domain (ATD) and ligand binding domain (LBD) undergo different structural rearrangements when paired with GluN3 subunits than in canonical receptors when they are paired with any of the four GluN2s. We observe unique conformations whose order and ligand dependence suggest a mechanism for paradoxical N1-mediated inhibition. Patch clamp recordings have been unable to detect single-channel currents, so these smFRET measurements represent the first single molecule measurements on these receptors.

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