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.

Taste Receptors in the Gastrointestinal Tract II.l-Amino acid sensing by calcium-sensing receptors: implications for GI physiology

2006 ◽  
Vol 291 (5) ◽  
pp. G753-G761 ◽  
Author(s):  
Arthur D. Conigrave ◽  
Edward M. Brown
Keyword(s):  
Amino Acid ◽  
Gastrointestinal Tract ◽  
Epithelial Transport ◽  
Hormone Secretion ◽  
Calcium Sensing Receptor ◽  
Calcium Sensing ◽  
Gut Hormone ◽  
Protein Ingestion ◽  
Amino Acid Sensing ◽  
Amino Acid Sensor

The extracellular calcium-sensing receptor (CaR) is a multimodal sensor for several key nutrients, notably Ca2+ions and l-amino acids, and is expressed abundantly throughout the gastrointestinal tract. While its role as a Ca2+ion sensor is well recognized, its physiological significance as an l-amino acid sensor and thus, in the gastrointestinal tract, as a sensor of protein ingestion is only now coming to light. This review focuses on the CaR’s amino acid sensing properties at both the molecular and cellular levels and considers new and putative physiological roles for the CaR in the amino acid-dependent regulation of gut hormone secretion, epithelial transport, and satiety.

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.

scholarly journals Structural insights into the activation of human calcium-sensing receptor

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Xiaochen Chen ◽  
Lu Wang ◽  
Qianqian Cui ◽  
Zhanyu Ding ◽  
Li Han ◽  
...  
Keyword(s):  
Amino Acid ◽  
Conformational Changes ◽  
Bound States ◽  
Large Scale ◽  
Transmembrane Domains ◽  
Structural Basis ◽  
Calcium Sensing Receptor ◽  
Calcium Sensing ◽  
Activation Mechanisms ◽  
G Protein Coupled

Human calcium-sensing receptor (CaSR) is a G-protein-coupled receptor that maintains Ca2+ homeostasis in serum. Here, we present the cryo-electron microscopy structures of the CaSR in the inactive and agonist+PAM bound states. Complemented with previously reported structures of CaSR, we show that in addition to the full inactive and active states, there are multiple intermediate states during the activation of CaSR. We used a negative allosteric nanobody to stabilize the CaSR in the fully inactive state and found a new binding site for Ca2+ ion that acts as a composite agonist with L-amino acid to stabilize the closure of active Venus flytraps. Our data show that agonist binding leads to compaction of the dimer, proximity of the cysteine-rich domains, large-scale transitions of 7-transmembrane domains, and inter- and intrasubunit conformational changes of 7-transmembrane domains to accommodate downstream transducers. Our results reveal the structural basis for activation mechanisms of CaSR and clarify the mode of action of Ca2+ ions and L-amino acid leading to the activation of the receptor.

scholarly journals Activation of the SPS Amino Acid-Sensing Pathway in Saccharomyces cerevisiae Correlates with the Phosphorylation State of a Sensor Component, Ptr3

2007 ◽  
Vol 28 (2) ◽  
pp. 551-563 ◽  
Author(s):  
Zhengchang Liu ◽  
Janet Thornton ◽  
Mário Spírek ◽  
Ronald A. Butow
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Amino Acids ◽  
Amino Acid ◽  
Nuclear Translocation ◽  
Proteolytic Processing ◽  
Casein Kinase I ◽  
Positive Regulators ◽  
Amino Acid Permeases ◽  
Amino Acid Sensing ◽  
Amino Acid Sensor

ABSTRACT Cells of the budding yeast Saccharomyces cerevisiae sense extracellular amino acids and activate expression of amino acid permeases through the SPS-sensing pathway, which consists of Ssy1, an amino acid sensor on the plasma membrane, and two downstream factors, Ptr3 and Ssy5. Upon activation of SPS signaling, two transcription factors, Stp1 and Stp2, undergo Ssy5-dependent proteolytic processing that enables their nuclear translocation. Here we show that Ptr3 is a phosphoprotein whose hyperphosphorylation is increased by external amino acids and is dependent on Ssy1 but not on Ssy5. A deletion mutation in GRR1, encoding a component of the SCFGrr1 E3 ubiquitin ligase, blocks amino acid-induced hyperphosphorylation of Ptr3. We found that two casein kinase I (CKI) proteins, Yck1 and Yck2, previously identified as positive regulators of SPS signaling, are required for hyperphosphorylation of Ptr3. Loss- and gain-of-function mutations in PTR3 result in decreased and increased Ptr3 hyperphosporylation, respectively. We found that a defect in PP2A phosphatase activity leads to the hyperphosphorylation of Ptr3 and constitutive activation of SPS signaling. Two-hybrid analysis revealed interactions between the N-terminal signal transduction domain of Ssy1 with Ptr3 and Yck1. Our findings reveal that CKI and PP2A phosphatase play antagonistic roles in SPS sensing by regulating Ptr3 phosphorylation.

scholarly journals Structural insights into the activation of human calcium-sensing receptor

2021 ◽  
Author(s):  
Xiaochen Chen ◽  
Lu Wang ◽  
Zhanyu Ding ◽  
Qianqian Cui ◽  
Li Han ◽  
...  
Keyword(s):  
Conformational Changes ◽  
Large Scale ◽  
Transmembrane Domains ◽  
Structural Basis ◽  
Calcium Sensing Receptor ◽  
Calcium Sensing ◽  
Cryo Electron Microscopy ◽  
Activation Mechanisms ◽  
G Protein Coupled ◽  
Structural Insights

AbstractHuman calcium-sensing receptor (CaSR) is a G-protein-coupled receptor that maintains Ca2+ homeostasis in serum. Here, we present the cryo-electron microscopy structures of the CaSR in the inactive and active states. Complemented with previously reported crystal structures of CaSR extracellular domains, it suggests that there are three distinct conformations: inactive, intermediate and active state during the activation. We used a negative allosteric nanobody to stabilize the CaSR in the fully inactive state and found a new binding site for Ca2+ ion that acts as a composite agonist with L-amino acid to stabilize the closure of active Venus flytraps. Our data shows that the agonist binding leads to the compaction of the dimer, the proximity of the cysteine-rich domains, the large-scale transitions of 7-transmembrane domains, and the inter-and intrasubunit conformational changes of 7-transmembrane domains to accommodate the downstream transducers. Our results reveal the structural basis for activation mechanisms of the CaSR.

scholarly journals Nonessential amino acid usage for protein replenishment in humans: a method of estimation

2019 ◽  
Vol 110 (2) ◽  
pp. 255-264 ◽  
Author(s):  
Paolo Tessari
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Protein Quality ◽  
Essential Amino Acids ◽  
World Health ◽  
Whole Body ◽  
Published Data ◽  
Total Proteins ◽  
Body Protein ◽  
Amino Acid Turnover

ABSTRACT Background Essential amino acids (EAAs) are key factors in determining dietary protein quality. Their RDAs have been estimated. However, although nonessential amino acids (NEAAs) are utilized for protein synthesis too, no estimates of their usage for body protein replenishment have been proposed so far. Objective The aim of this study was to provide minimum, approximate estimates of NEAA usage for body protein replenishment/conservation in humans. Methods A correlation between the pattern of both EAAs and NEAAs in body proteins, and their usage, was assumed. In order to reconstruct an “average” amino acid pattern/composition of total body proteins (as grams of amino acid per gram of protein), published data of relevant human organs/tissues (skeletal muscle, liver, kidney, gut, and collagen, making up ∼74% of total proteins) were retrieved. The (unknown) amino acid composition of residual proteins (∼26% of total proteins) was assumed to be the same as for the sum of the aforementioned organs excluding collagen. Using international EAA RDA values, an average ratio of EAA RDA to the calculated whole-body EAA composition was derived. This ratio was then used to back-calculate NEAA usage for protein replenishment. The data were calculated also using estimated organ/tissue amino acid turnover. Results The individual ratios of World Health Organization/Food and Agriculture Organization/United Nations University RDA to EAA content ranged between 1.35 (phenylalanine + tyrosine) and 3.68 (leucine), with a mean ± SD value of 2.72 ± 0.81. In a reference 70-kg subject, calculated NEAA usage for body protein replenishment ranged from 0.73 g/d for asparagine to 3.61 g/d for proline. Use of amino acid turnover data yielded similar results. Total NEAA usage for body protein replenishment was ∼19 g/d (45% of total NEAA intake), whereas ∼24 g/d was used for other routes. Conclusion This method may provide indirect minimum estimates of the usage of NEAAs for body protein replacement in humans.

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