Architecture and structural dynamics of the heteromeric GluK2/K5 kainate receptor
- Weill Cornell Medical College, United States
- McGill University, Canada
Abstract
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.
Data availability
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
Article and author information
Author details
Patricia MGE Brown
Funding
Leon Levy Foundation (N/A)
- Joel Meyerson
Fonds de Recherche du Québec - Santé (N/A)
- Patricia MGE Brown
Canadian Institutes of Health Research (136832)
- Derek Bowie
Canadian Institutes of Health Research (162317)
- Derek Bowie
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Copyright
© 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.
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Architecture and structural dynamics of the heteromeric GluK2/K5 kainate receptor
eLife 10:e66097.
https://doi.org/10.7554/eLife.66097
Further reading
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- Neuroscience
At many vertebrate synapses, presynaptic functions are tuned by expression of different Cav2 channels. Most invertebrate genomes contain only one Cav2 gene. The Drosophila Cav2 homolog, cacophony (cac), induces synaptic vesicle release at presynaptic active zones (AZs). We hypothesize that Drosophila cac functional diversity is enhanced by two mutually exclusive exon pairs that are not conserved in vertebrates, one in the voltage sensor and one in the loop binding Caβ and Gβγ subunits. We find that alternative splicing in the voltage sensor affects channel activation voltage. Only the isoform with the higher activation voltage localizes to AZs at the glutamatergic Drosophila larval neuromuscular junction and is imperative for normal synapse function. By contrast, alternative splicing at the other alternative exon pair tunes multiple aspects of presynaptic function. While expression of one exon yields normal transmission, expression of the other reduces channel number in the AZ and thus release probability. This also abolishes presynaptic homeostatic plasticity. Moreover, reduced channel number affects short-term plasticity, which is rescued by increasing the external calcium concentration to match release probability to control. In sum, in Drosophila alternative splicing provides a mechanism to regulate different aspects of presynaptic functions with only one Cav2 gene.
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- Structural Biology and Molecular Biophysics
We present near-atomic-resolution cryoEM structures of the mammalian voltage-gated potassium channel Kv1.2 in open, C-type inactivated, toxin-blocked and sodium-bound states at 3.2 Å, 2.5 Å, 3.2 Å, and 2.9 Å. These structures, all obtained at nominally zero membrane potential in detergent micelles, reveal distinct ion-occupancy patterns in the selectivity filter. The first two structures are very similar to those reported in the related Shaker channel and the much-studied Kv1.2–2.1 chimeric channel. On the other hand, two new structures show unexpected patterns of ion occupancy. First, the toxin α-Dendrotoxin, like Charybdotoxin, is seen to attach to the negatively-charged channel outer mouth, and a lysine residue penetrates into the selectivity filter, with the terminal amine coordinated by carbonyls, partially disrupting the outermost ion-binding site. In the remainder of the filter two densities of bound ions are observed, rather than three as observed with other toxin-blocked Kv channels. Second, a structure of Kv1.2 in Na+ solution does not show collapse or destabilization of the selectivity filter, but instead shows an intact selectivity filter with ion density in each binding site. We also attempted to image the C-type inactivated Kv1.2 W366F channel in Na+ solution, but the protein conformation was seen to be highly variable and only a low-resolution structure could be obtained. These findings present new insights into the stability of the selectivity filter and the mechanism of toxin block of this intensively studied, voltage-gated potassium channel.
