Extracellular Calcium Modulates Actions of Orthosteric and Allosteric Ligands on Metabotropic Glutamate Receptor 1 alpha

• Type of Material: Article
• Authors: Jason Y. Jiang, Georgia State University; Mulpuri Nagaraju, Georgia State University; Rebecca C. Meyer, Emory University; Li Zhang, Emory University; Donald Hamelberg, Georgia State University; Randy Hall, Emory University; Edward M. Brown, Brigham and Women's Hospital; P. Jeffrey Conn, Vanderbilt University; Jenny J. Yang, Georgia State University
• Language: English
• Date: 2014-01-17
• Publisher: The American Society for Biochemistry and Molecular Biology
• Publication Version: Final Published Version
• Copyright Statement: © 2014 by The American Society for Biochemistry and Molecular Biology, Inc.
• Final Published Version (URL): http://dx.doi.org/10.1074/jbc.M113.507665
• Title of Journal or Parent Work: Journal of Biological Chemistry
• Volume: 289
• Issue: 3
• Start Page: 1649
• End Page: 1661
• Grant/Funding Information: This work was also supported by a Brains and Behavior fellowship (to Y. J.).; This work was supported, in whole or in part, by National Institutes of Health Grants GM081749-01 (to J. J. Y.), DK078331 (to E. M. B.), and NS055179 (to R. A. H.).
• Keywords: CPCCOET; Biochemistry & Molecular Biology; Calcium; Antagonist; Binding-site; Molecular mechanism; G Protein-coupled Receptors (GPCR); Life Sciences & Biomedicine; Orthosteric Antagonist; Drug Discovery; Calcium-binding Proteins; Science & Technology; Allosteric Modulators; CA2+- binding sites; Structural basis; Orthosteric Agonist; Domain; Glutamate Receptors Metabotropic; Identification; Activation; CA2+
• Research Categories: Health Sciences, Pharmacology; Biology, Molecular; Chemistry, Biochemistry

Abstract

Metabotropic glutamate receptor 1α (mGluR1α), a member of the family C G protein-coupled receptors, is emerging as a potential drug target for various disorders, including chronic neuronal degenerative diseases. In addition to being activated by glutamate, mGluR1α is also modulated by extracellular Ca2+. However, the underlying mechanism is unknown. Moreover, it has long been challenging to develop receptor-specific agonists due to homologies within the mGluR family, and the Ca2+-binding site(s) on mGluR1α may provide an opportunity for receptor-selective targeting by therapeutics. In the present study, we show that our previously predicted Ca2+-binding site in the hinge region of mGluR1α is adjacent to the site where orthosteric agonists and antagonists bind on the extracellular domain of the receptor. Moreover, we found that extracellular Ca2+ enhanced mGluR1α-mediated intracellular Ca2+ responses evoked by the orthosteric agonist L-quisqualate. Conversely, extracellular Ca2+ diminished the inhibitory effect of the mGluR1α orthosteric antagonist (S)-α-methyl-4- carboxyphenylglycine. In addition, selective positive (Ro 67-4853) and negative (7-(hydroxyimino)cyclopropa[b]chromen-1acarboxylate ethyl ester) allosteric modulators of mGluR1α potentiated and inhibited responses to extracellular Ca2+, respectively, in a manner similar to their effects on the response of mGluR1α to glutamate. Mutations at residues predicted to be involved in Ca2+ binding, including E325I, had significant effects on the modulation of responses to the orthosteric agonist L-quisqualate and the allosteric modulator Ro 67-4853 by extracellular Ca2+. These studies reveal that binding of extracellular Ca2+ to the predicted Ca2+- binding site in the extracellular domain of mGluR1α modulates not only glutamate-evoked signaling but also the actions of both orthosteric ligands and allosteric modulators on mGluR1α.