Mechanism of Partial Agonism at the GluR2 AMPA Receptor: Measurements of Lobe Orientation in Solution

Maltsev, Alexander S.; Ahmed, Ahmed H.; Fenwick, Michael K.; Jane, David E.; Oswald, Robert E.

doi:10.1021/bi800843c

Cited by 37 publications

(72 citation statements)

References 47 publications

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“…According to this hypothesis, channel activation would require the fully closed form, and the stability of that form would dictate efficacy. The binding of some weak partial agonists, such as iodowillardiine (IW), are consistent with this idea in that a wide range of lobe closures have been observed in crystal (12,20) and NMR structures (15), and evidence for large scale dynamics is present in the NMR spectra (15,21). Also, mutations that decrease the efficacy of AMPA show a range of lobe orientations as measured using single molecule FRET (22).…”

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confidence: 60%

“…Two sets of double cysteine mutations were made on a wild type background of the GluA2 LBD: A452C/S652C and V484C/E657C. Both expressed well in E. coli and produced high quality NMR spectra when uniformly labeled with 15 N. The 1 H, 15 N-HSQC spectrum of V484C/ E657C bound to glutamate was unchanged when exposed to either Cu-phenanthroline or DTT (supplemental Fig. S1A).…”

Section: Lobe-locking Mutations-the Ligand-binding Domain Ofmentioning

confidence: 99%

“…Exchange of ligand was done in the presence of 50 mM DTT to remove glutamate and allow binding of the partial agonist. The 1 H, 15 N-HSQC (TROSY) NMR spectra (after the removal of DTT) are shown in Fig. 1, B (IW) and C (kainate).…”

Section: Lobe-locking Mutations-the Ligand-binding Domain Ofmentioning

confidence: 99%

“…A full closure would result in a high probability of gating, and with a partial closure, the probability of gating would be much lower. However, subsequent studies indicated that at least some partial agonists could assume a range of lobe closures (15), and even the correlation in crystal structures between lobe opening and efficacy does not always hold (16 -18). Most strikingly, crystal structures of partial agonists of the NMDA receptor show a fully closed lobe (19), leading to the suggestion that partial agonism is fundamentally different for NMDA versus AMPA receptors.…”

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confidence: 99%

“…Most strikingly, crystal structures of partial agonists of the NMDA receptor show a fully closed lobe (19), leading to the suggestion that partial agonism is fundamentally different for NMDA versus AMPA receptors. An alternative view of partial agonism is that the stability of full lobe closure dictates efficacy (13,15). That is, partial agonists could potentially exist in a dynamic equilibrium among two or more conformations.…”

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confidence: 99%

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Mechanism of AMPA Receptor Activation by Partial Agonists

Ahmed

Wang

Chuang

et al. 2011

Journal of Biological Chemistry

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The mechanism by which agonist binding to an ionotropic glutamate receptor leads to channel opening is a central issue in molecular neurobiology. Partial agonists are useful tools for studying the activation mechanism because they produce full channel activation with lower probability than full agonists. Structural transitions that determine the efficacy of partial agonists can provide information on the trigger that begins the channel-opening process. The ligand-binding domain of AMPA receptors is a bilobed structure, and the closure of the lobes is associated with channel activation. One possibility is that partial agonists sterically block full lobe closure but that partial degrees of closure trigger the channel with a lower probability. Alternatively, full lobe closure may be required for activation, and the stability of the fully closed state could determine efficacy with the fully closed state having a lower stability when bound to partial relative to full agonists. Disulfide-trapping experiments demonstrated that even extremely low efficacy ligands such as 6-cyano-7-nitroquinoxaline-2,3-dione can produce a full lobe closure, presumably with low probability. The results are consistent the hypothesis that the efficacy is determined at least in part by the stability of the state in which the lobes are fully closed.Ionotropic glutamate receptors are the major mediators of excitatory synaptic transmission in the vertebrate nervous system (1, 2). Glutamate receptor subunits are categorized by pharmacological properties, biological role, and sequence into those that are sensitive to the following: 1) ␣-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA; GluA1-4) 2 ; 2) the neurotoxin kainate (GluK1-5); and 3) N-methyl-D-aspartic acid (NMDA; GluN1, GluN2A-D, GluN3A-B). The important structural details of glutamate receptors were determined first by the solution of the structures of the ligand-binding domain (3-7) and the N-terminal domain (8, 9) followed by the structure of the full-length tetrameric GluA2 subtype of AMPA receptor (10). The structures in the presence of various agonists, partial agonists, and antagonists in combination with spectroscopic measurements, electrophysiological measurements, and site-directed mutagenesis have provided a wealth of information on the link between structure and function (11-13). The binding domain is a bilobed structure to which agonist binds in the cleft between the two lobes. Two linker peptide strands connect the lobes, and the lobes can close to envelope the agonist. One lobe (lobe 1) forms a dimer interface with a second copy of the ligand-binding domain within the tetrameric structure, and the second lobe (lobe 2) is linked to the ion channel domain. When the dimer interface is intact, the force generated by the closing of the lobes can affect the ion channel and presumably open a gate allowing ions to traverse the channel. Complexities arise due to the tetrameric structure and subtle differences between glutamate receptor subtypes, but the general outline of...

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confidence: 60%

Section: Lobe-locking Mutations-the Ligand-binding Domain Ofmentioning

confidence: 99%

Section: Lobe-locking Mutations-the Ligand-binding Domain Ofmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Mechanism of AMPA Receptor Activation by Partial Agonists

Ahmed

Wang

Chuang

et al. 2011

Journal of Biological Chemistry

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Structure of the S1S2 glutamate binding domain of GLuR3

et al. 2008

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Glutamate receptors are the most prevalent excitatory neurotransmitter receptors in the vertebrate central nervous system. Determining the structural differences between the binding sites of different subtypes is crucial to our understanding of neuronal circuits and to the development of subtype specific drugs. The structures of the binding domain (S1S2) of the GluR3 (flip) AMPA receptor subunit bound to glutamate and AMPA and the GluR2 (flop) subunit bound to glutamate were determined by X-ray crystallography to 1.9, 2.1, and 1.55 Å, respectively. Overall, the structure of GluR3 (flip) S1S2 is very similar to GluR2 (flop) S1S2 (backbone RMSD of 0.30 ± 0.05 for glutamate-bound and 0.26 ± 0.01 for AMPA-bound). The differences in the flip and flop isoforms are subtle and largely arise from one hydrogen bond across the dimer interface and associated water molecules. Comparison of the binding affinity for various agonists and partial agonists suggest that the S1S2 domains of GluR2 and GluR3 show only small differences in affinity, unlike what is found for the intact receptors (with the exception of one ligand, Cl-HIBO, which has a ten-fold difference in affinity for GluR2 vs GluR3).

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