The Three-dimensional Structure of an Ionotropic Glutamate Receptor Reveals a Dimer-of-dimers Assembly

Tichelaar, Willem; Safferling, Markus; Keinänen, Kari; Stark, Holger; Madden, Dean R.

doi:10.1016/j.jmb.2004.09.048

Cited by 105 publications

(95 citation statements)

References 27 publications

(37 reference statements)

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“…Two of these were formed from dimers of AMPA-like dimers. A dimer of dimers assembly (27) for iGluRs is now supported both by electrophysiological data identifying functional 2-fold symmetry (11, 34) and a recently described structure for GluR2 determined by electron microscopy (35). Despite this, it is still generally thought that, from analogy with potassium channels, the pore will be Ϸ4-fold, distorted to a greater or lesser extent.…”

Section: Resultsmentioning

confidence: 91%

Structure of the kainate receptor subunit GluR6 agonist-binding domain complexed with domoic acid

Nanao

Green

Stern‐Bach

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

120

142

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We report the crystal structure of the glycosylated ligand-binding (S1S2) domain of the kainate receptor subunit GluR6, in complex with the agonist domoate. The structure shows the expected overall homology with AMPA and NMDA receptor subunit structures but reveals an unexpected binding mode for the side chain of domoate, in which contact is made to the larger lobe only (lobe I). In common with the AMPA receptor subunit GluR2, the GluR6 S1S2 domain associates as a dimer, with many of the interdimer contacts being conserved. Subtle differences in these contacts provide a structural explanation for why GluR2 L483Y and GluR3 L507Y are nondesensitizing, but GluR6, which has a tyrosine at that site, is not. The structure incorporates native glycosylation, which has not previously been described for ionotropic glutamate receptors. The position of the sugars near the subunit interface rules out their direct involvement in subunit association but leaves open the possibility of indirect modulation. Finally, we observed several tetrameric assemblies that satisfy topological constraints with respect to connection to the receptor pore, and which are therefore candidates for the native quaternary structure.crystal structure ͉ domoate ͉ glutamate receptor I onotropic glutamate receptors (iGluRs) are major mediators of rapid excitatory neurotransmission in the mammalian CNS and in consequence are involved in a wide range of physiological and pathological neural processes (1). There are three main iGluR subfamilies: AMPA, NMDA, and kainate receptors. The functional importance of both AMPA and NMDA receptors in synaptic transmission and plasticity has long been recognized. It is only recently, however, that the physiological roles of kainate receptors have begun to be delineated. Studies using selective ligands and gene ablation in mice have shown that kainate receptors are involved in the regulation of synaptic transmission and plasticity in several brain regions (2).All iGluRs are thought to share a similar overall structure, with four homologous subunits arranged around a central cationselective pore. The subunits themselves share a common membrane topology (Fig. 1A), with three transmembrane domains (termed M1, M3, and M4) and a reentrant loop similar to the P loop found in potassium channels (termed M2). This leaves two large polypeptide domains on the extracellular (synaptic) side of the membrane: the Ϸ530-aa N terminus and the domain between M3 and M4. Studies of chimeric receptors and recombinant constructs identified the Ϸ120-aa preceding M1 (termed S1) and the Ϸ140-aa M3-M4 loop (S2) as forming the agonist-binding domain (3, 4). The S1S2 domain can be expressed as a soluble polypeptide independently of the membrane-spanning domains, making it amenable to crystallization and structure determination by x-ray diffraction. In this way, structures for the S1S2 domains for the AMPA-selective subunit GluR2 (5-7) and the NMDA subunit NR1 (8) have been determined, with both proteins sharing a bilobate structure. Although no str...

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Section: Resultsmentioning

confidence: 91%

Structure of the kainate receptor subunit GluR6 agonist-binding domain complexed with domoic acid

Nanao

Green

Stern‐Bach

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

120

142

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“…On the other hand, GluR␦2-NTD assembled into a stable homodimer. The NTD of ionotropic GluRs (iGluRs) with a tetrameric structure assembles as a dimer of dimers (Schorge and Colquhoun, 2003;Tichelaar et al, 2004;Midgett and Madden, 2008;Kumar et al, 2009), and tetrameric iGluRs have twofold symmetry rather than fourfold symmetry (Armstrong and Gouaux, 2000;Sobolevsky et al, 2004Sobolevsky et al, , 2009Nanao et al, 2005).…”

Section: Tetrameric Glur␦2 For Synapse Formationmentioning

confidence: 99%

GluRδ2 Assembles Four Neurexins intoTrans-Synaptic Triad to Trigger Synapse Formation

Lee¹,

Uemura²,

Yoshida³

et al. 2012

J. Neurosci.

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Elucidation of molecular mechanisms of synapse formation is a prerequisite for the understanding of neural wiring, higher brain functions, and mental disorders. The trans-synaptic interaction of postsynaptic glutamate receptor ␦2 (GluR␦2) and presynaptic neurexins (NRXNs) through cerebellin precursor protein 1 (Cbln1) mediates synapse formation in vivo in the cerebellum. Here, we asked how the trans-synaptic triad induces synapse formation. Native GluR␦2 existed as a tetramer in the membrane, whereas the N-terminal domain (NTD) of GluR␦2 formed a stable homodimer. When incubated with cultured mouse cerebellar granule cells (GCs), dimeric GluR␦2-NTD and Cbln1 exerted little effect on the accumulation of punctate immunostaining signals for Bassoon and vesicular glutamate transporter 1 in GC axons. However, tetramerized GluR␦2-NTD stimulated the accumulation of these presynaptic proteins in the axons. Analysis of Cbln1 mutants suggested that the binding sites of GluR␦2 and NRXN1␤ on Cbln1 are differential. Furthermore, there was no competition in the binding to Cbln1 between GluR␦2-NTD and the extracellular domain (ECD) of NRXN1␤. Thus, GluR␦2 and Cbln1 interacted with each other rather independently of Cbln1-NRXN1␤ interaction and vice versa. Gel filtration and isothermal titration calorimetry analyses consistently showed that dimeric GluR␦2-NTD and hexameric Cbln1 assembled in the 1:1 ratio, whereas hexameric Cbln1 and the laminin-neurexin-sex hormone-binding globulin domain of NRXN1␤-ECD assembled in the 1:2 ratio. Thus, the synaptogenic triad is assembled from tetrameric GluR␦2, hexameric Cbln1, and monomeric NRXN in the ratio of 1:2:4. These results suggest that GluR␦2 triggers synapse formation by clustering four NRXNs through triad formation.

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“…Allosteric potentiators (Jin et al, 2005) bind at the dimer interface, whereas disruptive mutations within the interface accelerate the rate of desensitization (Horning and Mayer, 2004). Kinetic (Bowie and Lange, 2002;Yelshansky et al, 2004) and electron microscopic (Tichelaar et al, 2004) studies also show that the key functional unit of AMPA receptors is a dimer. Most recently, it has been shown that NMDA subunit S1S2 domains form twofold dimers that are stabilized by mutations equivalent to R2 L483Y (Furukawa et al, 2005).…”

Section: Introductionmentioning

confidence: 98%

Interface Interactions Modulating Desensitization of the Kainate-Selective Ionotropic Glutamate Receptor Subunit GluR6

Zhang

Nayeem²,

Nanao³

et al. 2006

J. Neurosci.

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Ionotropic glutamate receptors from the AMPA and kainate subfamilies share many functional and structural features, but it is unclear whether this similarity extends to the molecular mechanisms underlying receptor desensitization. The current model for desensitization in AMPA receptors involves the rearrangement of dimers formed between subunit agonist binding domains. Key evidence for this has come from a single point mutant (from leucine to tyrosine) that abolished desensitization and that was shown to stabilize the binding domain dimer. However, the desensitization of kainate receptors appears to differ from that of AMPA receptors in several key respects. Although the kinetics of AMPA receptor gating and desensitization are consistent with channels formed from two dimers, similar evidence for the functional involvement of dimers has not been found in kainate receptors. Furthermore, despite the homolog of the nondesensitizing tyrosine in AMPA subunits also being a tyrosine in wild-type kainate subunits, these receptors desensitize rapidly and completely. Using mutagenesis based on the crystal structure of the glutamate receptor subunit GluR6 S1S2 domain in complex with domoate, we identified four residues neighboring this tyrosine that differ between AMPA and kainate subunits and that contribute to the different desensitization kinetics of these receptors. Detailed analysis of the effects of mutations at these sites confirms that there is in fact a common general mechanism for desensitization in non-NMDA receptors, dependent on the stability of the binding domain dimer interface, and reveals the existence of potential agonist-specific desensitization pathways.

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The Three-dimensional Structure of an Ionotropic Glutamate Receptor Reveals a Dimer-of-dimers Assembly

Cited by 105 publications

References 27 publications

Structure of the kainate receptor subunit GluR6 agonist-binding domain complexed with domoic acid

Structure of the kainate receptor subunit GluR6 agonist-binding domain complexed with domoic acid

GluRδ2 Assembles Four Neurexins intoTrans-Synaptic Triad to Trigger Synapse Formation

Interface Interactions Modulating Desensitization of the Kainate-Selective Ionotropic Glutamate Receptor Subunit GluR6

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