title: Energetics of glutamate receptor ligand binding domain dimer assembly are modulated by allosteric ions.
abstract: The activity of many ligand-gated ion channels and cell surface receptors is modulated by small molecules and ions, but an understanding of the underlying molecular mechanisms is scarce. For kainate, but not AMPA subtype glutamate receptors, the binding of Na(+) and Cl(-) ions to discrete, electrostatically coupled sites in the extracellular ligand binding domain (LBD) dimer assembly regulates the rate of entry into the desensitized state, which occurs when the dimer interface ruptures and the channel closes. Studies on glutamate receptors have defined the LBD dimer assembly as a key functional unit that controls activation and desensitization. Here we use analytical ultracentrifugation to probe the energetic effects of allosteric ions on kainate receptor dimer stability in solution, using a GluR6 mutant that desensitizes slowly. Our results show that sodium and chloride ions modulate kainate receptor dimer affinity as much as 50-fold, and that removal of either Cl(-) or Na(+) disrupts the dimer. The applicability of a similar allosteric mechanism for modulation of delta2 glutamate receptors by Ca(2+) was also tested. Our results indicate that ions can contribute substantial free energy to active state stabilization in both these receptors, and provide quantitative measurements of the energetic consequences of allosteric ion binding to a ligand-gated ion channel.
authors.affiliation: Laboratory of Cellular and Molecular Neurophysiology, Porter Neuroscience Research Center, National Institute of Child Health and Human Development, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20892, USA.
authors.forename: Charu
authors.initials: C
authors.lastname: Chaudhry
authors.forename: Andrew J R
authors.initials: AJ
authors.lastname: Plested
authors.forename: Peter
authors.initials: P
authors.lastname: Schuck
authors.forename: Mark L
authors.initials: ML
authors.lastname: Mayer
mesh_terms: D000494:Allosteric Regulation; D000595:Amino Acid Sequence; D001665:Binding Sites / Q000235:genetics; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002460:Cell Line; D002712:Chlorides / Q000737:chemistry* / Q000378:metabolism; D004735:Energy Transfer; D007700:Kinetics; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D018092:Kainic Acid Receptors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012964:Sodium / Q000737:chemistry* / Q000378:metabolism; D014461:Ultracentrifugation; D000097806:GluK2 Kainate Receptor
chemical_list: D002118:Calcium; D002712:Chlorides; D008024:Ligands; D018092:Kainic Acid Receptors; D012964:Sodium; D000097806:GluK2 Kainate Receptor