Kainate receptors (KARs) are L-glutamate-gated ion channels that regulate synaptic transmission and modulate neuronal circuits. KARs have strict assembly rules and primarily function as heteromeric receptors in the brain. A longstanding question is how KAR heteromer subunits organize and coordinate together to fulfill their signature physiological roles. Here we report structures of the GluK2/GluK5 heteromer in apo, antagonist-bound, and desensitized states. The receptor assembles with two copies of each subunit, ligand binding domains arranged as two heterodimers, and GluK5 subunits proximal to the channel. Strikingly, during desensitization GluK2 but not GluK5 subunits undergo major structural rearrangements to facilitate channel closure. We show how the large conformational differences between antagonist-bound and desensitized states are mediated by the linkers connecting the pore helices to the ligand-binding domains. This work presents the first KAR heteromer structure, reveals how its subunits are organized, and resolves how the heteromer can accommodate functionally-distinct closed channel structures.
Cryo-EM density maps have been deposited in the Electron Microscopy Data Bank (EMDB) under accession numbers EMD-23017 (GluK2/K5-apo), EMD-23014 (GluK2/K5-CNQX), and EMD-23015 (GluK2/K5-L-Glu). Model coordinates have been deposited in the Protein Data Bank (PDB) under accession numbers 7KS0 (GluK2/K5-CNQX) and 7KS3 (GluK2/K5-L-Glu). Raw cryo-EM data will be publicly available on the EMPIAR repository upon publication under the accession numbers: EMPIAR-10658, EMPIAR-10659, EMPIAR-10660
Glu2/K5 apoEMPIAR, EMPIAR-10658.
GluK2/K5 with 6-Cyano-7-nitroquinoxaline-2,3-dione (CNQX)EMPIAR, EMPIAR-10659.
GluK2/K5 with L-GluEMPIAR, EMPIAR-10660.
- Joel Meyerson
- Patricia MGE Brown
- Derek Bowie
- Derek Bowie
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
- Merritt Maduke, Stanford University School of Medicine, United States
© 2021, Khanra et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
Subthalamic nucleus deep brain stimulation (STN DBS) relieves many motor symptoms of Parkinson's Disease (PD), but its underlying therapeutic mechanisms remain unclear. Since its advent, three major theories have been proposed: (1) DBS inhibits the STN and basal ganglia output; (2) DBS antidromically activates motor cortex; and (3) DBS disrupts firing dynamics within the STN. Previously, stimulation-related electrical artifacts limited mechanistic investigations using electrophysiology. We used electrical artifact-free GCaMP fiber photometry to investigate activity in basal ganglia nuclei during STN DBS in parkinsonian mice. To test whether the observed changes in activity were sufficient to relieve motor symptoms, we then combined electrophysiological recording with targeted optical DBS protocols. Our findings suggest that STN DBS exerts its therapeutic effect through the disruption of movement-related STN activity, rather than inhibition or antidromic activation. These results provide insight into optimizing PD treatments and establish an approach for investigating DBS in other neuropsychiatric conditions.
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