# Mechanistic Basis of Calcium Sensing Receptor Signaling

> **NIH NIH R01** · STANFORD UNIVERSITY · 2024 · $261,326

## Abstract

ABSTRACT: Mechanistic Basis of Calcium Sensing Receptor Signaling
The calcium sensing receptor (CaSR) is the master regulator of calcium metabolism in human and represents
an outstanding drug target for the treatment of parathyroid disorders that develop in patients with chronic kidney
diseases (CKDs). For patients with renal disfunction that develop hyperparathyroidism, calcimimetic drugs that
act as positive allosteric modulators (PAMs) of the CaSR are the favored therapeutics. PAMs, such as cinacalcet,
evocalcet and etelcalcetide, are approved treatment for CKD; however, their clinical use is limited due to their
adverse side effects. By elucidating the dynamic structural mechanisms of receptor activation, its modulation by
small-molecule modulators, and the specificity of G protein activation, we seek to understand in detail the CaSR
signaling mechanism and enable the rational design of improved therapeutics modulating receptor function.
CaSR is a family C member of G protein-coupled receptors (GPCRs), which also include the metabotropic
glutamate receptors (mGlus) and the metabotropic gamma aminobutyric acid receptor (GABAB). Like other
members of this family, CaSR functions as an obligate homodimer with an N-terminal extracellular domain (ECD)
responsible for ligand binding, linked to the seven-transmembrane (7TM) domain. We have recently determined
cryo-electron microscopy (cryoEM) structures of the near-full-length human CaSR homodimer in active and
inactive states, revealing how ECD rearrangement upon Ca2+ binding induces the activation of the 7TMs and
how allosteric modulators engage the receptor. Our results illustrate an essential asymmetry in the active state
where each CaSR protomer is stabilized by a PAM molecule bound to each 7TM in two distinct conformations
leading to the activation of only one transmembrane region, priming it for G protein coupling. Here we propose
to extend these studies in order to characterize the mechanism and specificity of G protein activation by CaSR,
its dynamics, as well as the detailed action of allosteric modulators with distinct pharmacological interest.
Specifically, we seek to apply: structure-based mutagenesis coupled with cell signaling assays that monitor the
effects of allosteric modulators; cryoEM structural studies of CaSR alone and in complex with allosteric
modulators and distinct G proteins in a near native lipid environment; and single-molecule fluorescence
resonance energy transfer (smFRET) complemented by double electron-electron (DEER) spectroscopy to reveal
the dynamics of receptor and G protein activation as well as its modulation by different allosteric ligands.
Collectively, the proposed structural, cellular, biochemical and biophysical experiments aim to provide a full
mechanistic framework for transmembrane signaling by CaSR and will guide the future development of novel
drugs targeting this receptor.

## Key facts

- **NIH application ID:** 10814865
- **Project number:** 5R01DK132902-03
- **Recipient organization:** STANFORD UNIVERSITY
- **Principal Investigator:** Georgios Skiniotis
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $261,326
- **Award type:** 5
- **Project period:** 2022-04-01 → 2024-09-22

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10814865

## Citation

> US National Institutes of Health, RePORTER application 10814865, Mechanistic Basis of Calcium Sensing Receptor Signaling (5R01DK132902-03). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10814865. Licensed CC0.

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