Mechanism of conductance control and neurosteroid binding in NMDA receptors
Article Date: 29 October 2025
Article URL: https://www.nature.com/articles/s41586-025-09695-4
Article Image: none provided
Summary
This study uses high-resolution cryo-EM, electrophysiology (TEVC and single-channel), molecular dynamics and PMF calculations to map how neurosteroids and small-molecule modulators control conductance in GluN1a–GluN2B NMDA receptors. The authors solved multiple ligand-bound states (non-active, pre-active, closed, sub-open and fully open) with pregnenolone sulfate (PS), 24S-hydroxycholesterol (24S-HC) and the biased modulator EU1622-240. Distinct binding sites and binding poses were visualised: 24S-HC occupies a juxtamembrane pocket that promotes a pre-M1′ movement and stabilises pore opening, PS wedges between M2’/M3′ helices with a different effect, and EU1622-240 favours a sub-open conformation while reducing Ca2+ permeability. Structural findings are supported by functional recordings and simulations that detail changes in pore radius, hydration and ion energy barriers, highlighting the Asn-ring and VIVI-gate as key determinants of conductance and permeation.
Key Points
- Cryo-EM captured multiple functional states of GluN1a–GluN2B NMDAR bound to PS, 24S-HC and EU1622-240, revealing state-dependent ligand binding modes.
- 24S-HC binds a juxtamembrane pocket on GluN2B, promoting pre-M1′ movement and aiding the bending/dilation of M3′ helices required for pore opening.
- PS occupies a distinct site and uses a different wedge-like pose; PS and 24S-HC produce additive potentiation when combined.
- EU1622-240 stabilises a sub-open state and lowers Ca2+ permeability, demonstrating that conductance and ion selectivity can be biased by ligands.
- Electrophysiology (TEVC and single-channel) confirms changes in conductance and gating consistent with the structural states.
- MD and PMF calculations show modest energy barriers at the Thr-ring for Na+ permeation and highlight the Asn-ring as a secondary gate influencing ion binding and selectivity.
- The work identifies discrete allosteric pockets that can be exploited to tune NMDA receptor open probability, conductance and Ca2+ permeability — important for therapeutic modulation.
Why should I read this?
Short version: these folks actually mapped where neurosteroids and a small molecule latch on and how that changes the gate mechanics of NMDA receptors. If you care about designing safer NMDA modulators or understanding how endogenous sterols control synaptic signalling, the cryo-EM maps + electrophysiology here are gold. Read the figures for the exact pockets and the Supplementary/Extended Data if you’re thinking drug design or mechanistic follow-ups — they nailed the structural-functional link.