scholarly journals Calcium Sensing Receptor Activation by a Calcimimetic Suggests a Link between Cooperativity and Intracellular Calcium Oscillations

2002 ◽  
Vol 277 (51) ◽  
pp. 49691-49699 ◽  
Author(s):  
Susanne Miedlich ◽  
Lucio Gama ◽  
Gerda E. Breitwieser
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Intracellular Calcium ◽  
Receptor Activation ◽  
Calcium Oscillations ◽  
Calcium Stores ◽  
Calcium Sensing Receptor ◽  
Hek 293 ◽  
Calcium Sensing ◽  
Intracellular Ca

Activation of the calcium sensing receptor (CaR) by small increments in extracellular calcium (Ca2+e) induces intracellular calcium (Ca2+i) oscillations that are dependent on thapsigargin-sensitive intracellular calcium stores. Phenylalkylamines such as NPS R-568 are allosteric modulators (calcimimetics) that activate CaR by increasing the apparent affinity of the receptor for calcium. We determined, by fluorescence imaging with fura-2, whether the calcimimetic NPS R-568 could activate Ca2+ioscillations in HEK-293 cells expressing human CaR. NPS R-568 was more potent than Ca2+eat eliciting Ca2+ioscillations, particularly at low [Ca2+]e(as low as 0.1 mm). The oscillation frequencies elicited by NPS R-568 varied over a 2-fold range from peak to peak intervals of 60–70 to 30–45 s, depending upon the concentrations of both Ca2+eand NPS R-568. Finally, NPS R-568 induced sustained (>15 min after drug removal) Ca2+ioscillations, suggesting slow release of the drug from its binding site. We exploited the potency of NPS R-568 for eliciting Ca2+ioscillations for structural studies. Truncation of the CaR carboxyl terminus from 1077 to 886 amino acids had no effect on the ability of Ca2+or NPS R-568 to induce Ca2+ioscillations, but further truncation (to 868 amino acids) eliminated both highly cooperative Ca2+-dependent activation and regular Ca2+ioscillations. Alanine scanning within the amino acid sequence from Arg873to His879reveals a linkage between the cooperativity for Ca2+-dependent activation and establishment and maintenance of intracellular Ca2+oscillations. The amino acid residues critical to both functions of CaR may contribute to interactions with either G proteins or between CaR monomers within the functional dimer.

Calcium-sensing receptor activation induces intracellular calcium oscillations

2001 ◽  
Vol 280 (6) ◽  
pp. C1412-C1421 ◽  
Author(s):  
Gerda E. Breitwieser ◽  
Lucio Gama
Keyword(s):  
Kinase Inhibitors ◽  
Hormone Secretion ◽  
Low Frequency ◽  
Receptor Activation ◽  
Calcium Oscillations ◽  
Protein Kinase Inhibitors ◽  
Hek 293 ◽  
Calcium Sensing ◽  
Intracellular Ca ◽  
S Peak

Parathyroid hormone secretion is exquisitely sensitive to small changes in serum Ca2+concentration, and these responses are transduced via the Ca2+-sensing receptor (CaR). We utilized heterologous expression in HEK-293 cells to determine the effects of small, physiologically relevant perturbations in extracellular Ca2+ on CaR signaling via phosphatidylinositol-phospholipase C, using changes in fura 2 fluorescence to quantify intracellular Ca2+. Chronic exposure of CaR-transfected cells to Ca2+ in the range from 0.5 to 3 mM modulated the resting intracellular Ca2+concentration and the subsequent cellular responses to acute extracellular Ca2+ perturbations but had no effect on thapsigargin-sensitive Ca2+ stores. Modest, physiologically relevant increases in extracellular Ca2+concentration (0.5 mM increments) caused sustained (30–40 min) low-frequency oscillations of intracellular Ca2+ (∼45 s peak to peak interval). Oscillations were eliminated by 1 μM thapsigargin but were insensitive to protein kinase inhibitors (staurosporine, KN-93, or bisindolylmaleimide I). Staurosporine did increase the fraction of cells oscillating at a given extracellular Ca2+ concentration. Serum Ca2+ concentrations thus chronically regulate cells expressing CaR, and small perturbations in extracellular Ca2+ alter both resting intracellular Ca2+ as well as Ca2+ dynamics.

scholarly journals Structural mechanism of cooperative activation of the human calcium-sensing receptor by Ca2+ ions and L-tryptophan

Cell Research ◽  
2021 ◽  
Author(s):  
Shenglong Ling ◽  
Pan Shi ◽  
Sanling Liu ◽  
Xianyu Meng ◽  
Yingxin Zhou ◽  
...  
Keyword(s):  
Amino Acids ◽  
Conformational Changes ◽  
Bound States ◽  
Close Contact ◽  
Receptor Activation ◽  
Active State ◽  
Structural Level ◽  
Calcium Sensing Receptor ◽  
Calcium Sensing ◽  
Class C

AbstractThe human calcium-sensing receptor (CaSR) is a class C G protein-coupled receptor (GPCR) responsible for maintaining Ca2+ homeostasis in the blood. The general consensus is that extracellular Ca2+ is the principal agonist of CaSR. Aliphatic and aromatic L-amino acids, such as L-Phe and L-Trp, increase the sensitivity of CaSR towards Ca2+ and are considered allosteric activators. Crystal structures of the extracellular domain (ECD) of CaSR dimer have demonstrated Ca2+ and L-Trp binding sites and conformational changes of the ECD upon Ca2+/L-Trp binding. However, it remains to be understood at the structural level how Ca2+/L-Trp binding to the ECD leads to conformational changes in transmembrane domains (TMDs) and consequent CaSR activation. Here, we determined the structures of full-length human CaSR in the inactive state, Ca2+- or L-Trp-bound states, and Ca2+/L-Trp-bound active state using single-particle cryo-electron microscopy. Structural studies demonstrate that L-Trp binding induces the closure of the Venus flytrap (VFT) domain of CaSR, bringing the receptor into an intermediate active state. Ca2+ binding relays the conformational changes from the VFT domains to the TMDs, consequently inducing close contact between the two TMDs of dimeric CaSR, activating the receptor. Importantly, our structural and functional studies reveal that Ca2+ ions and L-Trp activate CaSR cooperatively. Amino acids are not able to activate CaSR alone, but can promote the receptor activation in the presence of Ca2+. Our data provide complementary insights into the activation of class C GPCRs and may aid in the development of novel drugs targeting CaSR.

scholarly journals Calcium-sensing receptor in GtoPdb v.2021.3

2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
Daniel Bikle ◽  
Hans Bräuner-Osborne ◽  
Edward M. Brown ◽  
Wenhan Chang ◽  
Arthur Conigrave ◽  
...  
Keyword(s):  
Amino Acids ◽  
Ionic Strength ◽  
Receptor Activation ◽  
Extracellular Ph ◽  
Allosteric Modulators ◽  
Calcium Sensing Receptor ◽  
Calcium Sensing ◽  
Trivalent Cations ◽  
Amino Acid Binding ◽  
Peptide Analogues

The calcium-sensing receptor (CaS, provisional nomenclature as recommended by NC-IUPHAR [47] and subsequently updated [77]) responds to multiple endogenous ligands, including extracellular calcium and other divalent/trivalent cations, polyamines and polycationic peptides, L-amino acids (particularly L-Trp and L-Phe), glutathione and various peptide analogues, ionic strength and extracellular pH (reviewed in [78]). While divalent/trivalent cations, polyamines and polycations are CaS receptor agonists [14, 110], L-amino acids, glutamyl peptides, ionic strength and pH are allosteric modulators of agonist function [36, 47, 61, 108, 109]. Indeed, L-amino acids have been identified as "co-agonists", with both concomitant calcium and L-amino acid binding required for full receptor activation [148, 54]. The sensitivity of the CaS receptor to primary agonists is increased by elevated extracellular pH [18] or decreased extracellular ionic strength [109]. This receptor bears no sequence or structural relation to the plant calcium receptor, also called CaS.

Amino acids and Ca2+ stimulate different patterns of Ca2+ oscillations through the Ca2+-sensing receptor

2002 ◽  
Vol 282 (6) ◽  
pp. C1414-C1422 ◽  
Author(s):  
Steven H. Young ◽  
Enrique Rozengurt
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Oscillation Frequency ◽  
Aromatic Amino Acids ◽  
Oscillation Pattern ◽  
Hek 293 ◽  
293 Cells ◽  
Intracellular Ca ◽  
Baseline Values ◽  
Stimulation Of

We determined the effect of aromatic amino acid stimulation of the human extracellular Ca2+-sensing receptor (CaR) on intracellular Ca2+ concentration ([Ca2+]i) in single HEK-293 cells. Addition of l-phenylalanine or l-tryptophan (at 5 mM) induced [Ca2+]i oscillations from a resting state that was quiescent at 1.8 mM extracellular Ca2+concentration ([Ca2+]e). Each [Ca2+]i peak returned to baseline values, and the average oscillation frequency was ∼1 min−1 at 37°C. Oscillations were not induced or sustained if the [Ca2+]e was reduced to 0.5 mM, even in the continued presence of amino acid. Average oscillation frequency in response to an increase in [Ca2+]e (from 1.8 to 2.5–5 mM) was much higher (∼4 min−1) than that induced by aromatic amino acids. Oscillations in response to [Ca2+]e were sinusoidal whereas those induced by amino acids were transient. Thus both amino acids and Ca2+, acting through the same CaR, produce oscillatory increases in [Ca2+]i, but the resultant oscillation pattern and frequency allow the cell to discriminate which agonist is bound to the receptor.

Physiological significance of L-amino acid sensing by extracellular Ca2+-sensing receptors

2007 ◽  
Vol 35 (5) ◽  
pp. 1195-1198 ◽  
Author(s):  
A.D. Conigrave ◽  
H.-C. Mun ◽  
S.C. Brennan
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Threshold Concentration ◽  
Physiological Significance ◽  
Whole Body ◽  
Calcium Sensing Receptor ◽  
Calcium Sensing ◽  
Amino Acid Sensing ◽  
G Protein Coupled ◽  
Receptor Family

The calcium-sensing receptor is a multimodal, multimetabolic sensor that mediates the feedback-dependent control of whole body calcium metabolism. Remarkably, in addition to its role in Ca2+o (extracellular Ca2+) sensing, the CaR (Ca2+-sensing receptor) also responds to L-amino acids. L-amino acids appear to activate, predominantly, a signalling pathway coupled with intracellular Ca2+ mobilization, require a threshold concentration of Ca2+o for efficacy and sensitize the receptor to activation by Ca2+o. Here, we review the evidence that the CaR, like other closely related members of the class 3 GPCR (G-protein-coupled receptor) family including GPRC6A, is a broad-spectrum amino acid-sensing receptor, consider the nature of the signalling response to amino acids and discuss its physiological significance.

scholarly journals Calcium-sensing receptor (version 2020.5) in the IUPHAR/BPS Guide to Pharmacology Database

2020 ◽  
Vol 2020 (5) ◽  
Author(s):  
Daniel Bikle ◽  
Hans Bräuner-Osborne ◽  
Edward M. Brown ◽  
Wenhan Chang ◽  
Arthur Conigrave ◽  
...  
Keyword(s):  
Amino Acids ◽  
Ionic Strength ◽  
Receptor Activation ◽  
Extracellular Ph ◽  
Allosteric Modulators ◽  
Calcium Sensing Receptor ◽  
Calcium Sensing ◽  
Trivalent Cations ◽  
Amino Acid Binding ◽  
Peptide Analogues

The calcium-sensing receptor (CaS, provisional nomenclature as recommended by NC-IUPHAR [46] and subsequently updated [76]) responds to multiple endogenous ligands, including extracellular calcium and other divalent/trivalent cations, polyamines and polycationic peptides, L-amino acids (particularly L-Trp and L-Phe), glutathione and various peptide analogues, ionic strength and extracellular pH (reviewed in [77]). While divalent/trivalent cations, polyamines and polycations are CaS receptor agonists [14, 109], L-amino acids, glutamyl peptides, ionic strength and pH are allosteric modulators of agonist function [35, 46, 60, 107, 108]. Indeed, L-amino acids have been identified as "co-agonists", with both concomitant calcium and L-amino acid binding required for full receptor activation [147, 53]. The sensitivity of the CaS receptor to primary agonists is increased by elevated extracellular pH [17] or decreased extracellular ionic strength [108]. This receptor bears no sequence or structural relation to the plant calcium receptor, also called CaS.

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