Structural mechanism of ligand activation in human calcium-sensing receptor

  • Elife. 2016 Jul 19;5:e13662. doi: 10.7554/eLife.13662.
Yong Geng  1  2 ,  Lidia Mosyak  1 ,  Igor Kurinov  3 ,  Hao Zuo  1 ,  Emmanuel Sturchler  4 ,  Tat Cheung Cheng  1 ,  Prakash Subramanyam  5 ,  Alice P Brown  6 ,  Sarah C Brennan  6 ,  Hee-Chang Mun  6 ,  Martin Bush  1 ,  Yan Chen  1 ,  Trang X Nguyen  7 ,  Baohua Cao  1 ,  Donald D Chang  5 ,  Matthias Quick  7 ,  Arthur D Conigrave  6 ,  Henry M Colecraft  5 ,  Patricia McDonald  4 ,  Qing R Fan  1  8
Affiliations
  • 1. Department of Pharmacology, Columbia University, New York, United States.
  • 2. Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China.
  • 3. Department of Chemistry and Chemical Biology, Cornell University, Ithaca, United States.
  • 4. Department of Molecular Therapeutics, The Scripps Translational Science Institute, Jupiter, United States.
  • 5. Department of Physiology and Cellular Biophysics, Columbia University, New York, United States.
  • 6. School of Life and Environmental Sciences, University of Sydney, New South Wales, Australia.
  • 7. Department of Psychiatry, Columbia University, New York, United States.
  • 8. Department of Pathology and Cell Biology, Columbia University, New York, United States.
PMID: 27434672 DOI: 10.7554/eLife.13662
Abstract

Human calcium-sensing receptor (CaSR) is a G-protein-coupled receptor (GPCR) that maintains extracellular CA(2+) 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 CA(2+) and PO4(3-) ions. Both ions are crucial for structural integrity of the receptor. While CA(2+) 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.

Keywords
amino acids; biochemistry; biophysics; calcium-sensing receptor; extracellular calcium homeostasis; extracellular domain structure; human; principal agonist; receptor activation mechanism; structural biology.