Structural Dynamics of the Glycine-binding Domain of the N-Methyl-d-Aspartate Receptor |
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Authors: | Drew M Dolino David Cooper Swarna Ramaswamy Henriette Jaurich Christy F Landes Vasanthi Jayaraman |
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Institution: | From the ‡Center for Membrane Biology, Department of Biochemistry and Molecular Biology, Graduate School of Biomedical Sciences, University of Texas Health Science Center, Houston, Texas 77030 and ;the Departments of §Chemistry and ;¶Electrical and Computer Engineering, Rice University, Houston, Texas 77251 |
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Abstract: | N-Methyl-d-aspartate receptors mediate the slow component of excitatory neurotransmission in the central nervous system. These receptors are obligate heteromers containing glycine- and glutamate-binding subunits. The ligands bind to a bilobed agonist-binding domain of the receptor. Previous x-ray structures of the glycine-binding domain of NMDA receptors showed no significant changes between the partial and full agonist-bound structures. Here we have used single molecule fluorescence resonance energy transfer (smFRET) to investigate the cleft closure conformational states that the glycine-binding domain of the receptor adopts in the presence of the antagonist 5,7-dichlorokynurenic acid (DCKA), the partial agonists 1-amino-1-cyclobutanecarboxylic acid (ACBC) and l-alanine, and full agonists glycine and d-serine. For these studies, we have incorporated the unnatural amino acid p-acetyl-l-phenylalanine for specific labeling of the protein with hydrazide derivatives of fluorophores. The single molecule fluorescence resonance energy transfer data show that the agonist-binding domain can adopt a wide range of cleft closure states with significant overlap in the states occupied by ligands of varying efficacy. The difference lies in the fraction of the protein in a more closed-cleft form, with full agonists having a larger fraction in the closed-cleft form, suggesting that the ability of ligands to select for these states could dictate the extent of activation. |
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Keywords: | Fluorescence Resonance Energy Transfer (FRET) Glutamate Receptor Ion Channel Ionotropic Glutamate Receptor Ligand-binding Protein LRET NMDA Receptor Protein Dynamics Receptor Structure-Function |
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