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Related Concept Videos

ER Retrieval Pathway01:45

ER Retrieval Pathway

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In the secretory pathway, vesicles transport proteins from one cellular compartment to another in forward transport to deliver the protein to its correct location. Occasionally, misfolded proteins and incorrect proteins escape their original compartments, and a retrieval pathway is used to return the escaped proteins to their original compartment.
The ER uses many checkpoints to prevent the entry of incorrectly folded or a resident protein as cargo onto a transport vesicle. These mechanisms...
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Export of Misfolded Proteins out of the ER01:32

Export of Misfolded Proteins out of the ER

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After folding, the ER assesses the quality of secretory and membrane proteins. The correctly folded proteins are cleared by the calnexin cycle for transport to their final destination, while misfolded proteins are held back in the ER lumen. The ER chaperones attempt to unfold and refold the misfolded proteins but sometimes fail to achieve the correct native conformation. Such terminally misfolded proteins are then exported to the cytosol by ER-associated degradation or ERAD pathway for...
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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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Protein Folding Quality Check in the RER01:29

Protein Folding Quality Check in the RER

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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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Insertion of Single-pass Transmembrane Proteins in the RER01:26

Insertion of Single-pass Transmembrane Proteins in the RER

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Integral membrane proteins are proteins adhered to the lipid bilayer of a cell organelle or membrane. They can be of two types: transmembrane integral proteins that span the lipid bilayer and monotopic proteins that are attached to either side of the membrane but do not pass through it.
Integral transmembrane proteins possess transmembrane and extra membrane domains. The transmembrane domains are primarily made of 20-25 hydrophobic amino acids arranged in a helical secondary confirmation. These...
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Cotranslational Protein Translocation01:20

Cotranslational Protein Translocation

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Translocation of proteins across membranes is an ancient process that occurs even in bacteria and archaebacteria. In fact, the components of the translocation machinery are still conserved between prokaryotes and eukaryotes.
Sec61 channel partners for cotranslational translocation
During cotranslational translocation, the Sec61 channel partners with the signal recognition particle (SRP), the signal recognition particle receptor (SR), and the ribosomes to transport the nascent polypeptide chain...
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Related Experiment Video

Updated: Aug 11, 2025

Purification of the Membrane Compartment for Endoplasmic Reticulum-associated Degradation of Exogenous Antigens in Cross-presentation
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Purification of the Membrane Compartment for Endoplasmic Reticulum-associated Degradation of Exogenous Antigens in Cross-presentation

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CCPG1 recognizes endoplasmic reticulum luminal proteins for selective ER-phagy.

Shunsuke Ishii1, Haruka Chino2, Koji L Ode3

  • 1Department of Biology, Graduate School of Science and Engineering, Chiba University, Chiba 263-8522, Japan.

Molecular Biology of the Cell
|February 3, 2023
PubMed
Summary

Cell cycle progression 1 (CCPG1) acts as a bispecific receptor, mediating the ER-phagy of abnormal endoplasmic reticulum (ER) proteins like 6xIAPP and P3H4. This process ensures cellular homeostasis by clearing misfolded proteins via selective autophagy.

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Visualization and Quantification of Endogenous Intra-Organelle Protein Interactions at ER-Mitochondria Contact Sites by Proximity Ligation Assays
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Last Updated: Aug 11, 2025

Purification of the Membrane Compartment for Endoplasmic Reticulum-associated Degradation of Exogenous Antigens in Cross-presentation
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Visualization and Quantification of Endogenous Intra-Organelle Protein Interactions at ER-Mitochondria Contact Sites by Proximity Ligation Assays
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Visualization and Quantification of Endogenous Intra-Organelle Protein Interactions at ER-Mitochondria Contact Sites by Proximity Ligation Assays

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Area of Science:

  • Cell Biology
  • Molecular Biology
  • Autophagy Research

Background:

  • The endoplasmic reticulum (ER) is crucial for protein synthesis, folding, and modification.
  • ER quality control eliminates misfolded proteins, and ER-phagy (selective ER autophagy) maintains homeostasis.
  • Mechanisms for recognizing ER luminal proteins in ER-phagy remain poorly understood.

Purpose of the Study:

  • To elucidate the recognition mechanism of ER luminal proteins during ER-phagy.
  • To identify specific receptors and cargo involved in ER-phagy.
  • To understand how aberrant ER proteins are cleared to maintain cellular health.

Main Methods:

  • Utilized the aggregation-prone protein six-repeated islet amyloid polypeptide (6xIAPP) as a model ER-phagy substrate.
  • Investigated the role of cell cycle progression 1 (CCPG1) as an ER-phagy receptor.
  • Identified endogenous cargo proteins and characterized the interaction regions of CCPG1.

Main Results:

  • CCPG1 was identified as an ER-phagy receptor that mediates the degradation of 6xIAPP.
  • Prolyl 3-hydroxylase family member 4 (P3H4) was identified as an endogenous cargo of CCPG1-dependent ER-phagy.
  • CCPG1 possesses distinct cargo-interacting regions (CIRs) that bind different luminal proteins (6xIAPP and P3H4) and the autophagosomal membrane.

Conclusions:

  • CCPG1 functions as a bispecific ER-phagy receptor, recognizing both specific ER luminal cargos and the autophagosomal membrane.
  • This bispecificity facilitates the efficient removal of aberrant ER-resident proteins, maintaining ER and cellular homeostasis.
  • The study reveals a novel mechanism for selective ER protein degradation via ER-phagy.