Elucidation of a novel extracellular calcium-binding site on metabotropic glutamate receptor 1{alpha} (mGluR1{alpha}) that controls receptor activation.
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.
Jiang
Yusheng
Y
From the Department of Chemistry, Atlanta, Georgia 30303.
Huang
Yun
Y
From the Department of Chemistry, Atlanta, Georgia 30303.
Wong
Hing-Cheung
HC
From the Department of Chemistry, Atlanta, Georgia 30303.
Zhou
Yubin
Y
From the Department of Chemistry, Atlanta, Georgia 30303.
Wang
Xue
X
Department of Computer Science, Center for Drug Design and Advanced Biotechnology, Georgia State University, Atlanta, Georgia 30303.
Yang
Jun
J
Department of Toxicology, Hangzhou Normal University School of Public Health, Hangzhou, Zhejiang 310036, China.
Hall
Randy A
RA
Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322.
Brown
Edward M
EM
Division of Endocrinology, Diabetes, and Hypertension, Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115.
Yang
Jenny J
JJ
From the Department of Chemistry, Atlanta, Georgia 30303. Electronic address: chejjy@langate.gsu.edu.
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
D018094:Receptors, Metabotropic Glutamate; C104077:metabotropic glutamate receptor type 1; D018698:Glutamic Acid; D002118:Calcium