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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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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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Protein Folding Quality Check in the RER01:29

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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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Protein Translocation Machinery on the ER Membrane01:28

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The translocon complex situated on the ER membrane is the main gateway for the protein secretory pathway. It facilitates the transport of nascent peptides into the ER lumen and their insertion into the ER membrane.
Sec61 protein conducting channel
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Vesicular Tubular Clusters01:45

Vesicular Tubular Clusters

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After budding out from the ER membrane, some COPII vesicles lose their coat and fuse with one another to form larger vesicles and interconnected tubules called vesicular tubular clusters or VTCs. These clusters constitute a compartment at the ER-Golgi interface known as ERGIC (Endoplasmic Reticulum Golgi Intermediate Compartment). The ERGIC is a mobile membrane-bound cargo transport system that sorts proteins secreted from ER and delivers them to the Golgi.
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Directing Proteins to the Rough Endoplasmic Reticulum01:34

Directing Proteins to the Rough Endoplasmic Reticulum

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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: Nov 3, 2025

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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Ca2+ Regulates ERp57-Calnexin Complex Formation.

Yuya Tanikawa1, Shingo Kanemura1,2, Dai Ito3

  • 1School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337, Japan.

Molecules (Basel, Switzerland)
|June 2, 2021
PubMed
Summary

Calcium ions regulate the ERp57-calnexin complex, crucial for protein folding in the endoplasmic reticulum. This complex aids oxidative folding and prevents protein aggregation, maintaining cellular homeostasis.

Keywords:
Ca2+ERp57calnexinchaperoneendoplasmic reticulumhuman leukocyte antigenoxidative folding

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Cellular Biology

Background:

  • ERp57 is a key disulfide catalyst in the endoplasmic reticulum (ER) involved in protein folding.
  • ERp57 works with calnexin (CNX) and calreticulin (CRT) chaperones throughout protein folding.
  • Maintaining protein homeostasis is vital for cellular function and disease prevention.

Purpose of the Study:

  • To elucidate the regulatory mechanisms of calcium (Ca2+) on the ERp57-calnexin complex formation.
  • To understand the functional roles of the ERp57-CNX complex in protein folding and aggregation.

Main Methods:

  • Biochemical analyses were employed to study protein interactions.
  • Isothermal titration calorimetry (ITC) was used to quantify binding thermodynamics.
  • Functional assays assessed oxidative folding and client aggregation.

Main Results:

  • ERp57 binds strongly to CNX via non-covalent interactions in the absence of Ca2+.
  • The ERp57-CNX complex enhances oxidative folding of human leukocyte antigen heavy chains.
  • The complex also effectively inhibits client protein aggregation.

Conclusions:

  • Ca2+ plays a critical role in regulating the ERp57-calnexin interaction.
  • The ERp57-CNX complex exhibits both enzymatic and chaperoning functions, particularly under Ca2+ depletion.
  • These findings reveal molecular insights into the interplay between chaperone networks and Ca2+ in protein homeostasis.