Structural mechanism of ligand activation in human calcium-sensing receptor

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Abstract

Human calcium-sensing receptor (CaSR) is a G-protein coupled receptor (GPCR) that maintains extracellular Ca²⁺ homeostasis through the regulation of parathyroid hormone secretion. It functions as a disulfide-tethered homodimer composed of three main domains, the Venus Flytrap module, cysteine-rich domain, and seven-helix transmembrane region. Here we present the crystal structures of the entire extracellular domain of CaSR in the resting and active conformations. We provide direct evidence that L-amino acids are agonists of the receptor. In the active structure, L-Trp occupies the orthosteric agonist-binding site at the interdomain cleft, and is primarily responsible for inducing extracellular domain closure to initiate receptor activation. Our structures reveal multiple binding sites for Ca²⁺ and PO₄^3- ions. Both ions are crucial for structural integrity of the receptor. While Ca²⁺ ions stabilize the active state, PO₄^3- ions reinforce the inactive conformation. The activation mechanism of CaSR involves the formation of a novel dimer interface between subunits.

Data availability

The following data sets were generated

(2016) Crystal structure of the inactive form of human calcium-sensing receptor extracellular domain
Publicly available at the RCSB Protein Data Bank (accession no: 5K5T).

http://www.rcsb.org/pdb/search/structidSearch.do?structureId=5K5T
(2016) Crystal structure of the active form of human calcium-sensing receptor extracellular domain
Publicly available at the RCSB Protein Data Bank (accession no: 5K5S).

http://www.rcsb.org/pdb/search/structidSearch.do?structureId=5K5S

Article and author information

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Yong Geng

Department of Pharmacology, Columbia University, New York, United States

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Lidia Mosyak

Department of Pharmacology, Columbia University, New York, United States

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Igor Kurinov

Department of Chemistry and Chemical Biology, Cornell University, Ithaca, United States

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Hao Zuo

Department of Pharmacology, Columbia University, New York, United States

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Emmanuel Sturchler

Department of Molecular Therapeutics, The Scripps Translational Science Institute, Jupiter, United States

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Tat Cheung Cheng

Department of Pharmacology, Columbia University, New York, United States

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Prakash Subramanyam

Department of Physiology and Cellular Biophysics, Columbia University, New York, United States

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Alice P Brown

School of Life and Environmental Sciences, University of Sydney, New South Wales, Australia

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Sarah C Brennan

School of Life and Environmental Sciences, University of Sydney, New South Wales, Australia

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Hee-chang Mun

School of Life and Environmental Sciences, University of Sydney, New South Wales, Australia

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Martin Bush

Department of Pharmacology, Columbia University, New York, United States

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Yan Chen

Department of Pharmacology, Columbia University, New York, United States

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Trang X Nguyen

Department of Psychiatry, Columbia University, New York, United States

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Baohua Cao

Department of Pharmacology, Columbia University, New York, United States

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Donald D Chang

Department of Physiology and Cellular Biophysics, Columbia University, New York, United States

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Matthias Quick

Department of Psychiatry, Columbia University, New York, United States

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Arthur D Conigrave

School of Life and Environmental Sciences, University of Sydney, New South Wales, Australia

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Henry M Colecraft

Department of Physiology and Cellular Biophysics, Columbia University, New York, United States

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Patricia McDonald

Department of Molecular Therapeutics, The Scripps Translational Science Institute, Jupiter, United States

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The authors declare that no competing interests exist.
Qing R Fan

Department of Pharmacology, Columbia University, New York, United States

For correspondence
qf13@cumc.columbia.edu

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The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0002-9330-0963

Funding

National Institute of General Medical Sciences (R01GM112973)

Qing R Fan

American Heart Association (15GRNT25420002)

Qing R Fan

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Copyright

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.