3h6t
Crystal structure of the iGluR2 ligand-binding core (S1S2J-N754S) in complex with glutamate and cyclothiazide at 2.25 A resolutionCrystal structure of the iGluR2 ligand-binding core (S1S2J-N754S) in complex with glutamate and cyclothiazide at 2.25 A resolution
Structural highlights
FunctionGRIA2_RAT Receptor for glutamate that functions as ligand-gated ion channel in the central nervous system and plays an important role in excitatory synaptic transmission. L-glutamate acts as an excitatory neurotransmitter at many synapses in the central nervous system. Binding of the excitatory neurotransmitter L-glutamate induces a conformation change, leading to the opening of the cation channel, and thereby converts the chemical signal to an electrical impulse. The receptor then desensitizes rapidly and enters a transient inactive state, characterized by the presence of bound agonist. In the presence of CACNG4 or CACNG7 or CACNG8, shows resensitization which is characterized by a delayed accumulation of current flux upon continued application of glutamate.[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedIonotropic glutamate receptors (iGluRs) mediate fast excitatory neurotransmission. Upon glutamate application, 2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid receptors undergo rapid and almost complete desensitization that can be attenuated by positive allosteric modulators. The molecular mechanism of positive allosteric modulation has been elucidated previously by crystal structures of the ligand-binding core of iGluR2 in complex with, for example, cyclothiazide (CTZ). Here, we investigate the structure and function of CTZ and three closely related analogues NS1493, NS5206, and NS5217 at iGluR2, by X-ray crystallography and fast application patch-clamp electrophysiology. CTZ was the most efficacious and potent modulator of the four compounds on iGluR2(Q)(i) [E(max) normalized to response of glutamate: 754% (CTZ), 490% (NS1493), 399% (NS5206), and 476% (NS5217) and EC(50) in micromolar: 10 (CTZ), 26 (NS1493), 43 (NS5206), and 48 (NS5217)]. The four modulators divide into three groups according to efficacy and desensitization kinetics: (1) CTZ increases the peak current efficacy twice as much as the three analogues and nearly completely blocks receptor desensitization; (2) NS5206 and NS5217 have low efficacy and only attenuate desensitization partially; (3) NS1493 has low efficacy but nearly completely blocks receptor desensitization. A hydrophobic substituent at the 3-position of the 1,1-dioxo-3,4-dihydro-2H-benzo[e][1,2,4]thiadiazine ring system is important for compound efficacy, with the following ranking: norbornenyl (bicyclo[2.2.1]hept-2-ene)>cyclopentyl>methyl. The replacement of the norbornenyl moiety with a significantly less hydrophobic cyclopentane ring increases the flexibility of the modulator as the cyclopentane ring adopts various conformations at the iGluR2 allosteric binding site. The main structural feature responsible for a nearly complete block of desensitization is the presence of an NH hydrogen bond donor in the 4-position of the 1,1-dioxo-3,4-dihydro-2H-benzo[e][1,2,4]thiadiazine ring system, forming an anchoring hydrogen bond to Ser754. Therefore, the atom at the 4-position of CTZ seems to be a major determinant of receptor desensitization kinetics. Distinct structural features of cyclothiazide are responsible for effects on peak current amplitude and desensitization kinetics at iGluR2.,Hald H, Ahring PK, Timmermann DB, Liljefors T, Gajhede M, Kastrup JS J Mol Biol. 2009 Sep 4;391(5):906-17. Epub 2009 Jul 8. PMID:19591837[15] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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