title: Elucidation of a novel extracellular calcium-binding site on metabotropic glutamate receptor 1{alpha} (mGluR1{alpha}) that controls receptor activation.
abstract: Metabotropic glutamate receptor 1α (mGluR1α) exerts important effects on numerous neurological processes. Although mGluR1α is known to respond to extracellular Ca(2+) ([Ca(2+)](o)) and the crystal structures of the extracellular domains (ECDs) of several mGluRs have been determined, the calcium-binding site(s) and structural determinants of Ca(2+)-modulated signaling in the Glu receptor family remain elusive. Here, we identify a novel Ca(2+)-binding site in the mGluR1α ECD using a recently developed computational algorithm. This predicted site (comprising Asp-318, Glu-325, and Asp-322 and the carboxylate side chain of the receptor agonist, Glu) is situated in the hinge region in the ECD of mGluR1α adjacent to the reported Glu-binding site, with Asp-318 involved in both Glu and calcium binding. Mutagenesis studies indicated that binding of Glu and Ca(2+) to their distinct but partially overlapping binding sites synergistically modulated mGluR1α activation of intracellular Ca(2+) ([Ca(2+)](i)) signaling. Mutating the Glu-binding site completely abolished Glu signaling while leaving its Ca(2+)-sensing capability largely intact. Mutating the predicted Ca(2+)-binding residues abolished or significantly reduced the sensitivity of mGluR1α not only to [Ca(2+)](o) and [Gd(3+)](o) but also, in some cases, to Glu. The dual activation of mGluR1α by [Ca(2+)](o) and Glu has important implications for the activation of other mGluR subtypes and related receptors. It also opens up new avenues for developing allosteric modulators of mGluR function that target specific human diseases.
authors: From the Department of Chemistry, Atlanta, Georgia 30303.
authors: Yusheng
authors: Y
authors: Jiang
authors: From the Department of Chemistry, Atlanta, Georgia 30303.
authors: Yun
authors: Y
authors: Huang
authors: From the Department of Chemistry, Atlanta, Georgia 30303.
authors: Hing-Cheung
authors: HC
authors: Wong
authors: From the Department of Chemistry, Atlanta, Georgia 30303.
authors: Yubin
authors: Y
authors: Zhou
authors: Department of Computer Science, Center for Drug Design and Advanced Biotechnology, Georgia State University, Atlanta, Georgia 30303.
authors: Xue
authors: X
authors: Wang
authors: Department of Toxicology, Hangzhou Normal University School of Public Health, Hangzhou, Zhejiang 310036, China.
authors: Jun
authors: J
authors: Yang
authors: Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322.
authors: Randy A
authors: RA
authors: Hall
authors: Division of Endocrinology, Diabetes, and Hypertension, Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115.
authors: Edward M
authors: EM
authors: Brown
authors: From the Department of Chemistry, Atlanta, Georgia 30303. Electronic address: chejjy@langate.gsu.edu.
authors: Jenny J
authors: JJ
authors: Yang
mesh_terms: D000465:Algorithms; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray / Q000379:methods; D018698:Glutamic Acid / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D016296:Mutagenesis; D010449:Peptide Mapping / Q000379:methods; D017434:Protein Structure, Tertiary; D018094:Receptors, Metabotropic Glutamate / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology
chemical_list: D018094:Receptors, Metabotropic Glutamate; C104077:metabotropic glutamate receptor type 1; D018698:Glutamic Acid; D002118:Calcium