Tyr702 Is an Important Determinant of Agonist Binding and Domain Closure of the Ligand-Binding Core of GluR2

Abstract

Ionotropic glutamate receptors mediate most rapid excitatory synaptic transmission in the mammalian central nervous system, and their involvement in neurological diseases has stimulated widespread interest in their structure and function. Despite a large number of agonists developed so far, few display selectivity among (S)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl) propionic acid (AMPA)-receptor subtypes. The present study provides X-ray structures of the glutamate receptor 2 (GluR2)-selective partial agonist (S)-2-amino-3-(1,3,5,6,7-pentahydro-2,4-dioxocyclopenta[e] pyrimidin-1-yl) propanoic acid [(S)-CPW399] in complex with the ligand-binding core of GluR2 (GluR2-S1S2J) and with a (Y702F)GluR2-S1S2J mutant. In addition, the structure of the nonselective partial agonist kainate in complex with (Y702F)GluR2-S1S2J was determined. The results show that the selectivity of (S)-CPW399 toward full-length GluR2 relative to GluR3 is reflected in the binding data on the two soluble constructs, allowing the use of (Y702F)GluR2-S1S2J as a model system for studying GluR2/GluR3 selectivity. Structural comparisons suggest that selectivity arises from disruption of a watermediated network between ligand and receptor. A D1-D2 domain closure occurs upon agonist binding. (S)-CPW399 and kainate induce greater domain closure in the Y702F mutant, indicating that these partial agonists here act in a manner more reminiscent of full agonists. Both kainate and (S)-CPW399 exhibited higher efficacy at (Y702F)GluR2(Q) i than at wild-type GluR2(Q) i . Whereas an excellent correlation exists between domain closure and efficacy of a range of agonists at full-length GluR2 determined by electrophysiology in Xenopus laevis oocytes, a direct correlation between agonist induced domain closure of (Y702F)GluR2-S1S2J and efficacy at the GluR3 receptor is not observed. Although it clearly controls selectivity, mutation of this residue alone is insufficient to explain agonist-induced conformational rearrangements occurring in this variant.Binding of (S)-glutamate to ionotropic glutamate receptors (iGluRs) is a key step in the predominant mechanism of rapid excitatory synaptic transmission among nerve cells within the mammalian central nervous system. iGluRs are important in the development and function of the central nervous system and are implicated in learning and memory formation. Furthermore, iGluRs also seem to be associated with certain neurological and psychiatric diseases (e.g., Alzheimer-type diseases, Parkinson's disease, epilepsy, stroke, amyotrophic lateral sclerosis, and schizophrenia). Therefore, the iGluRs are considered potential drug targets (Dingledine et al., 1999;Brä uner-Osborne et al., 2000). The iGluRs have been divided into three different classes: the (S)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl) propionic acid (AMPA), The structures reported in this article have been deposited within the Protein Databank with accession numbers 1SYH, 1SYI, and 1XHY.Article, publication date, and citation information can be found at ...

Glutamate Receptor Ion Channels: Structure, Regulation, and Function

“…Furthermore, there is a direct correlation between the degree of domain closure with full and partial AMPA receptor agonists and the degree of desensitization produced by those agonists Frandsen et al, 2005). Thus, the degree of agonist-induced LBD closure seems to be the primary determinant of tension at the LBD dimer interface and thus governs transition into both the open and desensitized state.…”

“…Br-HIBO, an analog of ibotenic acid, preferentially activates GluA1 and GluA2 versus GluA3 and GluA4 receptors (Coquelle et al, 2000) through involvement of water-mediated hydrogen bonding to Tyr702 in GluA1 and GluA2, which is Phe in GluA3 and GluA4. Thus, ordered water molecules within the agonist binding site interact with the ligand to influence specificities among GluA subunits Hogner et al, 2002;Pentikä inen et al, 2003;Frandsen et al, 2005). Cl-HIBO was synthesized after molecular modeling predicted that the exchange of bromine for chlorine would improve selectivity (Bjerrum et al, 2003).…”

Distinct Structural Features of Cyclothiazide Are Responsible for Effects on Peak Current Amplitude and Desensitization Kinetics at iGluR2

“…4 The ligand-binding site is situated in a cleft between two domains, D1 and D2, which can move as rigid bodies independent of each other (i.e., as a clamshell-like structure), and agonist efficacy has been shown to correlate to the degree of domain closure upon agonist binding. 9,10 Together with functional data of full-length iGluRs, the crystal structures form the basis of a well-established model of AMPA receptor activation and desensitization. 4,9,11,12 Desensitization characteristics of iGluRs can be positively modulated by small allosteric modulators, ions, and plant lectins.…”

Binding Site Flexibility: Molecular Simulation of Partial and Full Agonists within a Glutamate Receptor

“…We would anticipate that such ligands would be even weaker agonists that kainate. The behavior of water surrounding subsite D principally reflects a key water identified in a series of crystallographic studies (Armstrong and Gouaux, 2000) and more recently has been suggested to play a central role in GluR1/GluR2 versus GluR3/GluR4 selectivity (Hogner et al, 2002;Frandsen et al, 2005).…”