Amin JB, Gochman A, He M, Certain N, Wollmuth LP. NMDA Receptors Require Multiple Pre-opening Gating Steps for Efficient Synaptic Activity.
Neuron 2020;
109:488-501.e4. [PMID:
33264592 DOI:
10.1016/j.neuron.2020.11.009]
[Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Revised: 10/06/2020] [Accepted: 11/11/2020] [Indexed: 12/27/2022]
Abstract
NMDA receptors (NMDARs) are glutamate-gated ion channels that mediate fast excitatory synaptic transmission in the nervous system. Applying glutamate to outside-out patches containing a single NMDAR, we find that agonist-bound receptors transition to the open state via two conformations, an "unconstrained pre-active" state that contributes to fast synaptic events and a "constrained pre-active" state that does not. To define how glutamate drives these conformations, we decoupled the ligand-binding domains from specific transmembrane segments for GluN1 and GluN2A. Displacements of the pore-forming M3 segments define the energy of fast opening. However, to enter the unconstrained conformation and contribute to fast signaling, the GluN2 pre-M1 helix must be displaced before the M3 segments move. This pre-M1 displacement is facilitated by the flexibility of the S2-M4 of GluN1 and GluN2A. Thus, outer structures-pre-M1 and S2-M4-work in concert to remove constraints and prime the channel for rapid opening, facilitating fast synaptic transmission.
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