External Ions Are Coactivators of Kainate Receptors

• Published in: The Journal of neuroscience 2006-05, Vol.26 (21), p.5750-5755
• Main Authors: Wong, Adrian Y. C, Fay, Anne-Marie L, Bowie, Derek
• Format: Article
• Language: English
• Subjects: Animals; Binding Sites; Brief Communications; Cell Line; Ion Channel Gating - drug effects; Ion Channel Gating - physiology; Ions; Membrane Potentials - drug effects; Membrane Potentials - physiology; Protein Binding; Receptors, AMPA - metabolism; Receptors, Kainic Acid - drug effects; Receptors, Kainic Acid - metabolism; Structure-Activity Relationship
• ISSN: 0270-6474; 1529-2401
• DOI: 10.1523/JNEUROSCI.0301-06.2006

The activation of ligand-gated ion channels is thought to depend solely on the binding of chemical neurotransmitters. In this study, we demonstrate that kainate (KA) ionotropic glutamate receptors (iGluRs) require not only the neurotransmitter L-glutamate (L-Glu) but also external sodium and chloride ions for activation. Removal of external ions traps KA receptors (KARs) in a novel inactive state that binds L-Glu with picomolar affinity. Moreover, occupancy of KARs by L-Glu precludes external ion binding, demonstrating crosstalk between ligand- and ion-binding sites. AMPA iGluRs function normally in the absence of external ions, revealing that even closely related iGluR subfamilies operate by distinct gating mechanisms. This behavior is interchangeable via a single amino acid residue that operates as a molecular switch to confer AMPA receptor behavior onto KARs. Our findings identify a novel allosteric site that singles out KARs from all other ligand-gated ion channels.