Ionotropic glutamate receptors principally mediate fast excitatory transmission in the brain. Among the three classes of ionotropic glutamate receptors, kainate receptors (KARs) have a unique brain ...distribution, which has been historically defined by (3)H-radiolabeled kainate binding. Compared with recombinant KARs expressed in heterologous cells, synaptic KARs exhibit characteristically slow rise-time and decay kinetics. However, the mechanisms responsible for these distinct KAR properties remain unclear. We found that both the high-affinity binding pattern in the mouse brain and the channel properties of native KARs are determined by the KAR auxiliary subunit Neto1. Through modulation of agonist binding affinity and off-kinetics of KARs, but not trafficking of KARs, Neto1 determined both the KAR high-affinity binding pattern and the distinctively slow kinetics of postsynaptic KARs. By regulating KAR excitatory postsynaptic current kinetics, Neto1 can control synaptic temporal summation, spike generation and fidelity.
Lessons from crystal structures of kainate receptors Møllerud, Stine; Frydenvang, Karla; Pickering, Darryl S. ...
Neuropharmacology,
January 2017, 2017-01-00, 20170101, Letnik:
112, Številka:
Pt A
Journal Article
Recenzirano
Kainate receptors belong to the family of ionotropic glutamate receptors. These receptors assemble from five subunits (GluK1-5) into tetrameric ion channels. Kainate receptors are located at both ...pre- and postsynaptic membranes in the central nervous system where they contribute to excitatory synaptic transmission and modulate network excitability by regulating neurotransmitter release. Dysfunction of kainate receptors has been implicated in several neurological disorders such as epilepsy, schizophrenia and depression. Here we provide a review on the current understanding of kainate receptor structure and how they bind agonists, antagonists and ions. The first structure of the ligand-binding domain of the GluK1 subunit was reported in 2005, seven years after publication of the crystal structure of a soluble construct of the ligand-binding domain of the AMPA-type subunit GluA2. Today, a full-length structure has been determined of GluK2 by cryo electron microscopy to 7.6 Å resolution as well as 84 high-resolution crystal structures of N-terminal domains and ligand-binding domains, including agonist and antagonist bound structures, modulatory ions and mutations. However, there are still many unanswered questions and challenges in front of us.
This article is part of the Special Issue entitled ‘Ionotropic glutamate receptors’.
Kainate receptors contribute to fast excitatory neurotransmission and have been linked to brain diseases. We provide a review on 84 crystal structures of N-terminal and ligand-binding domains of kainate receptors. Display omitted
•Kainate receptors belong to the family of ionotropic glutamate receptors.•These receptors are important for memory and learning.•A review on 84 crystal structures of kainate receptors is presented.•We discuss binding of agonists, antagonists, ions and mutations.
The surface expression and regulated endocytosis of kainate (KA) receptors (KARs) plays a critical role in neuronal function. PKC can modulate KAR trafficking, but the sites of action and molecular ...consequences have not been fully characterized. Small ubiquitin-like modifier (SUMO) modification of the KAR subunit GluK2 mediates agonist-evoked internalization, but how KAR activation leads to GluK2 SUMOylation is unclear. Here we show that KA stimulation causes rapid phosphorylation of GluK2 by PKC, and that PKC activation increases GluK2 SUMOylation both in vitro and in neurons. The intracellular C-terminal domain of GluK2 contains two predicted PKC phosphorylation sites, S846 and S868, both of which are phosphorylated in response to KA. Phosphomimetic mutagenesis of S868 increased GluK2 SUMOylation, and mutation of S868 to a nonphosphorylatable alanine prevented KA-induced SUMOylation and endocytosis in neurons. Infusion of SUMO-1 dramatically reduced KAR-mediated currents in HEK293 cells expressing WT GluK2 or nonphosphorylatable S846A mutant, but had no effect on currents mediated by the S868A mutant. These data demonstrate that agonist activation of GluK2 promotes PKC-dependent phosphorylation of S846 and S868, but that only S868 phosphorylation is required to enhance GluK2 SUMOylation and promote endocytosis. Thus, direct phosphorylation by PKC and GluK2 SUMOylation are intimately linked in regulating the surface expression and function of GluK2-containing KARs.
Starting from 1–4 and 7 structural templates, analogues based on bioisosteric replacements (5a–c vs 1, 2 and 6 vs 7) were synthesized for completing the SAR analysis. Interesting binding properties ...at GluA2, GluK1, and GluK3 receptors were discovered. The requirements for GluK3 interaction were elucidated by determining the X-ray structures of the GluK3-LBD with 2 and 5c and by computational studies. Antinociceptive potential was demonstrated for GluK1 partial agonist 3 and antagonist 7 (2 mg/kg ip).
Little is known about the molecular mechanisms underlying differences in the ligand binding properties of AMPA, kainate, and NMDA subtype glutamate receptors. Crystal structures of the GluR5 and ...GluR6 kainate receptor ligand binding cores in complexes with glutamate, 2S,4R-4-methylglutamate, kainate, and quisqualate have now been solved. The structures reveal that the ligand binding cavities are 40% (GluR5) and 16% (GluR6) larger than for GluR2. The binding of AMPA- and GluR5-selective agonists to GluR6 is prevented by steric occlusion, which also interferes with the high-affinity binding of 2S,4R-4-methylglutamate to AMPA receptors. Strikingly, the extent of domain closure produced by the GluR6 partial agonist kainate is only 3° less than for glutamate and 11° greater than for the GluR2 kainate complex. This, together with extensive interdomain contacts between domains 1 and 2 of GluR5 and GluR6, absent from AMPA receptors, likely contributes to the high stability of GluR5 and GluR6 kainate complexes.
Pseudo-nitzschia multiseries is a diatom species associated with the production of domoic acid (DA), a water soluble neurotoxin that is easily transferred up in the food web, causing devastating ...effects on top marine organisms and humans. Despite studies on Pseudo-nitzschia are relevant to human health safety, partitioning of marine toxins between intracellular and extracellular fractions are poorly documented. This study aimed to determine the growth rates and DA content, both intracellular and extracellular, of Pseudo-nitzschia multiseries cultures at three different light settings (15, 120 and 560 μmol m−2 s−1). The optimal conditions for cell growth were observed at 120 and 560 μmol m−2 s−1, whereas DA production was observed in P. multiseries at 15 and 120 μmol m−2 s−1, ranging between 0.18-2.56 and 0.16–3.5 pg DA cell−1, respectively. Higher intracellular DA concentrations were found during the senescence phase at low light intensity and during the exponential phase at medium light intensity, while higher concentrations of dissolved DA were found at low and medium light intensities in the senescence phase reaching 3 and 10 ng DA mL−1 respectively. The amount of toxin released into the culture medium represents the most important fraction ranging between 63 and 98% during the exponential phase and nearly 99% during the senescence phase. In contrast, under low light intensity, dissolved DA was detected in the culture medium only during the senescence phase. This study confirms the importance of light intensity on DA production and clearly shows that dissolved domoic acid is an important fraction in Pseudo-nitzschia cultures, suggesting with the careful assumptions of results from static cultures extrapolated to bloom situations that waterborne exposure of marine organism should be considered during blooms of Pseudo-nitzschia multiseries.
•Partition of intracellular and extracellular domoic acid was investigated in P. multiseries cell cultures.•Domoic acid levels were characterized under 3 irradiance levels (15, 120 and 560 μmol m−2 s−1).•Higher intracellular DA concentrations were found during the senescence phase at low light intensity.•At the medium light intensity higher intracellular DA concentrations were found at the exponential phase.•Extracellular levels were found at low and medium light intensities in the senescence phase.•Extracellular levels may represent up to 97% of the total domoic acid determined in the culture.
Domoic acid (DA) is a naturally occurring neurotoxin known to harm marine animals. DA-producing algal blooms are increasing in size and frequency. Although chronic exposure is known to produce brain ...lesions, the influence of DA toxicosis on behavior in wild animals is unknown. We showed, in a large sample of wild sea lions, that spatial memory deficits are predicted by the extent of right dorsal hippocampal lesions related to natural exposure to DA and that exposure also disrupts hippocampal-thalamic brain networks. Because sea lions are dynamic foragers that rely on flexible navigation, impaired spatial memory may affect survival in the wild.
Two decades have passed since the first report of the cloning of a kainate-type glutamate receptor (KAR) subunit. The intervening years have seen a rapid growth in our understanding of the ...biophysical properties and function of KARs in the brain. This research has led to an appreciation that KARs play very distinct roles at synapses relative to other members of the glutamate-gated ion channel receptor family, despite structural and functional commonalities. The surprisingly diverse and complex nature of KAR signaling underlies their unique impact upon neuronal networks through their direct and indirect effects on synaptic transmission, and their prominent role in regulating cell excitability. This review pieces together highlights from the two decades of research subsequent to the cloning of the first subunit, and provides an overview of our current understanding of the role of KARs in the CNS and their potential importance to neurological and neuropsychiatric disorders.
Glutamate receptors are ligand-gated tetrameric ion channels that mediate synaptic transmission in the central nervous system. They are instrumental in vertebrate cognition and their dysfunction ...underlies diverse diseases. In both the resting and desensitized states of AMPA and kainate receptor subtypes, the ion channels are closed, whereas the ligand-binding domains, which are physically coupled to the channels, adopt markedly different conformations. Without an atomic model for the desensitized state, it is not possible to address a central problem in receptor gating: how the resting and desensitized receptor states both display closed ion channels, although they have major differences in the quaternary structure of the ligand-binding domain. Here, by determining the structure of the kainate receptor GluK2 subtype in its desensitized state by cryo-electron microscopy (cryo-EM) at 3.8 Å resolution, we show that desensitization is characterized by the establishment of a ring-like structure in the ligand-binding domain layer of the receptor. Formation of this 'desensitization ring' is mediated by staggered helix contacts between adjacent subunits, which leads to a pseudo-four-fold symmetric arrangement of the ligand-binding domains, illustrating subtle changes in symmetry that are important for the gating mechanism. Disruption of the desensitization ring is probably the key switch that enables restoration of the receptor to its resting state, thereby completing the gating cycle.
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