Kinetic Contributions to Gating by Interactions Unique to N-methyl-d-aspartate (NMDA) Receptors

William F Borschel,Kirstie A Cummings,Leeann K Tindell,Gabriela K Popescu

doi:10.1074/jbc.m115.678656

William F Borschel, Kirstie A Cummings + Show 2 more

Open Access

https://doi.org/10.1074/jbc.m115.678656

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Abstract

Among glutamate-gated channels, NMDA receptors produce currents that subside with unusually slow kinetics, and this feature is essential to the physiology of central excitatory synapses. Relative to the homologous AMPA and kainate receptors, NMDA receptors have additional intersubunit contacts in the ligand binding domain that occur at both conserved and non-conserved sites. We examined GluN1/GluN2A single-channel currents with kinetic analyses and modeling to probe these class-specific intersubunit interactions for their role in glutamate binding and receptor gating. We found that substitutions that eliminate such interactions at non-conserved sites reduced stationary gating, accelerated deactivation, and imparted sensitivity to aniracetam, an AMPA receptor-selective positive modulator. Abolishing unique contacts at conserved sites also reduced stationary gating and accelerated deactivation. These results show that contacts specific to NMDA receptors, which brace the heterodimer interface within the ligand binding domain, stabilize actively gating receptor conformations and result in longer bursts and slower deactivations. They support the view that the strength of the heterodimer interface modulates gating in both NMDA and non-NMDA receptors and that unique interactions at this interface are responsible in part for basic differences between the kinetics of NMDA and non-NMDA currents at glutamatergic synapses.

Highlights

NMDA receptor deactivation is characteristically slow and depends on unique intersubunit contacts in the ligand binding domain
Site II Contacts Control NMDA Receptor Current Deactivation—The atomic structure of the N1/N2A receptor ligand binding domains (LBD) heterodimer revealed a group of intersubunit interactions that is absent in AMPA receptors [15]
N1 Tyr-535 plays a critical role in NMDA receptor deactivation, with increased hydrophobic contacts in the N1 Y535W (N1Y/W) mutant, dramatically slowing macroscopic current deactivation and reducing contacts as in the N1 Y535S

Summary

Introduction

NMDA receptor deactivation is characteristically slow and depends on unique intersubunit contacts in the ligand binding domain. Abolishing unique contacts at conserved sites reduced stationary gating and accelerated deactivation These results show that contacts specific to NMDA receptors, which brace the heterodimer interface within the ligand binding domain, stabilize actively gating receptor conformations and result in longer bursts and slower deactivations. They support the view that the strength of the heterodimer interface modulates gating in both NMDA and non-NMDA receptors and that unique interactions at this interface are responsible in part for basic differences between the kinetics of NMDA and nonNMDA currents at glutamatergic synapses

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