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Related Concept Videos

Calmodulin-dependent Signaling01:16

Calmodulin-dependent Signaling

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Calmodulin (CaM) is a calcium-binding protein in eukaryotes that controls various calcium-regulated cellular processes. It has four calcium-binding sites that bind calcium to form the calcium-calmodulin ( Ca2+-CaM) complex. GPCR stimulation increases the calcium levels in the cells that bind to CaM and induces a conformational change.
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ER is the primary site for the maturation and folding of soluble and transmembrane secretory proteins. The calnexin cycle is a specific chaperone system that folds and assesses the confirmation of N-glycosylated proteins before they can exit the ER lumen. The primary players of this quality check pipeline are the lectins, ER-resident chaperones, and a glucosyl transferase enzyme. In case the calnexin system in the lumen fails to salvage a misfolded protein, it is transported to the cytoplasm...
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Feedback Regulation of Calcium Concentration01:27

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Calcium is an essential signaling molecule required for various cellular functions. Calcium pumps and ion channels on cell and organellar membranes, such as those on the endoplasmic reticulum (ER), regulate calcium concentrations inside the cell. They remain closed, keeping the cytosolic calcium levels low at a resting state.
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Overview of Secretory Vesicles01:33

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Secretory vesicles, also known as dense core vesicles (DCVs), are membrane-bound vesicles that transport secretory proteins, such as hormones or neurotransmitters. Regulated secretory vesicles transport proteins from the trans-Golgi network to the exterior of the cell. Proteins present in regulated secretory vesicles are required to be rapidly exocytosed in large amounts upon a specific stimulus.
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Regulation of the Unfolded Protein Response01:31

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Inositol-requiring kinase one or IRE1 is the most conserved eukaryotic unfolded protein response (UPR) receptor. It is a type I transmembrane protein kinase receptor with a distinctive site-specific RNase activity. As the binding mechanics of the misfolded proteins with the N-terminal domain of IRE-1 are unclear, three binding models — direct, indirect, and allosteric -- are proposed for receptor activation. Nevertheless, it is known that once a misfolded protein associates with IRE1, it...
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The organelle-specific signaling sequences direct proteins synthesized in the cytosol to their final destination like ER, mitochondria, peroxisomes, etc. Some of the proteins directed to ER are then trafficked via vesicles to other organelles within the cell or the extracellular environment through the Golgi complex. For example, the rough ER synthesizes soluble proteins for transportation to the lysosomes or secretion out of the cell. It can also synthesize transmembrane proteins that can...
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Related Experiment Video

Updated: Mar 21, 2026

Live Cell Calcium Imaging Combined with siRNA Mediated Gene Silencing Identifies Ca2+ Leak Channels in the ER Membrane and their Regulatory Mechanisms
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Mapping the Ca(2+) induced structural change in calreticulin.

Sanne Grundvad Boelt1, Christoffer Norn2, Morten Ib Rasmussen3

  • 1Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK 5230 Odense, Denmark; Department of Autoimmunology and Biomarkers, Statens Serum Institut, Artillerivej 5, DK 2300 Copenhagen, Denmark.

Journal of Proteomics
|May 20, 2016
PubMed
Summary

Calcium (Ca2+) binding induces significant conformational changes in calreticulin, impacting its chaperone activity. These Ca2+-dependent structural shifts involve flexibility in the P-loop and stabilization of the C-terminal region.

Keywords:
BS(3) d(0)BS(3) d(4)CalreticulinChemical cross-linkingMass spectrometryMassAI softwareProtein structureRosetta modelling

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Direct Imaging of ER Calcium with Targeted-Esterase Induced Dye Loading TED
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Live Cell Calcium Imaging Combined with siRNA Mediated Gene Silencing Identifies Ca2+ Leak Channels in the ER Membrane and their Regulatory Mechanisms
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Monitoring ER/SR Calcium Release with the Targeted Ca2+ Sensor CatchER+

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Area of Science:

  • Biochemistry
  • Structural Biology
  • Molecular Biology

Background:

  • Calreticulin is a crucial endoplasmic reticulum chaperone involved in Ca(2+) homeostasis and MHC class I complex stabilization.
  • Existing high-resolution structures of calreticulin are incomplete, and Ca(2+)-induced conformational changes remain poorly understood.
  • The function of calreticulin as an endoplasmic reticulum chaperone is known to be modulated by Ca(2+) concentration, but the underlying structural mechanisms are unclear.

Purpose of the Study:

  • To investigate the Ca(2+)-induced conformational changes in calreticulin.
  • To elucidate the structural mechanism behind Ca(2+)-dependent regulation of calreticulin's chaperone activity.

Main Methods:

  • Utilized a combination of chemical cross-linking and mass spectrometry.
  • Employed bioinformatics analysis and computational modeling using Rosetta.
  • Investigated Ca(2+)-dependent structural alterations using a bifunctional linker.

Main Results:

  • Observed a significant change in the cross-linking pattern of calreticulin upon Ca(2+) binding.
  • Results indicate high flexibility in the P-loop region.
  • Demonstrated stabilization of the acidic C-terminal and a close interaction between the P-loop and C-terminal.

Conclusions:

  • Ca(2+) binding induces substantial conformational changes in calreticulin, affecting its structure and function.
  • These Ca(2+)-dependent structural rearrangements, particularly in the proline-rich loop, alter the accessibility of the peptide/lectin-binding site.
  • Ca(2+) regulation of calreticulin likely impacts its chaperone activity beyond simple Ca(2+) storage.