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Related Concept Videos

The Proteasome01:13

The Proteasome

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Eukaryotic cells can degrade proteins through several pathways. One of the most important among these is the ubiquitin-proteasome pathway. It helps the cell eliminate the misfolded, damaged, or unwarranted cytoplasmic proteins in a highly specific manner.
In this pathway, the target proteins are first tagged with small proteins called ubiquitin. This involves participation of a series of enzymes including— E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and E3...
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It is vital to regulate the activity of enzymatic as well as non-enzymatic proteins inside the cell. This can be achieved either through creating a balance between their rate of synthesis and degradation or regulating the intrinsic activity of the protein. Both these regulation mechanisms play an essential role in the normal functioning of cells.
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Eukaryotic cells use different mechanisms to eliminate toxic waste obsolete and worn-out substances. Lysosomes play a pivotal role in this, and hence, these substances are carried to the lysosome from other parts of the cell and extracellular space through different pathways. The most elaborately studied pathways to the lysosome are the endocytic pathways.
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Export of Misfolded Proteins out of the ER01:32

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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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The Proteasome Structure01:17

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The ubiquitin-proteasome pathway is a well-known mechanism utilized by eukaryotic cells to remove cytoplasmic proteins that are misfolded, damaged, or no longer needed. In this pathway, the protein that needs to be eliminated undergoes a process called ubiquitination, where a chain of ubiquitin molecules is attached to the 48th lysine residue of the target protein. This ubiquitin modification helps the proteasome distinguish between a target protein and a healthy protein.
The proteasome is an...
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Post-translational Translocation of Proteins to the RER01:27

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A sizable fraction of proteins destined for ER are first synthesized in the cell cytosol and then transported across the ER membrane–a process called post-translational translocation. Similar to cotranslationally translocated proteins, these proteins also use the Sec translocon complex to enter the ER lumen.
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Related Experiment Video

Updated: May 12, 2025

Profiling Ubiquitin and Ubiquitin-like Dependent Post-translational Modifications and Identification of Significant Alterations
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Cytosolic Delivery of Functional Ubiquitin.

JoLynn B Giancola1, Aniekan Okon1, Yanfeng Li2

  • 1Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.

Journal of Peptide Science : an Official Publication of the European Peptide Society
|May 9, 2025
PubMed
Summary

Researchers developed a method for delivering exogenous ubiquitin into human cells. This technique allows for the functional incorporation of ubiquitin into endogenous proteins, advancing ubiquitin biology research.

Keywords:
cytosoldeliveryendosomolytic peptideproteostasistracelessubiquitin

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Area of Science:

  • Cell Biology
  • Biochemistry
  • Molecular Biology

Background:

  • The proteostasis network regulates protein homeostasis through complex signaling.
  • Ubiquitination is crucial for cellular protein degradation but its intricate role is challenging to study.
  • Existing methods limit the investigation of exogenous ubiquitin's function in human cells.

Purpose of the Study:

  • To develop a novel strategy for delivering exogenous ubiquitin into the cytosol of human cells.
  • To investigate the functional incorporation of delivered ubiquitin into endogenous proteins.
  • To facilitate the study of semisynthetic ubiquitin variants in a cellular context.

Main Methods:

  • Application of a traceless protein delivery system.
  • Coadministration of endosomolytic peptides L17E and L17ER4 for cytosolic access.
  • Monitoring of ubiquitin uptake and incorporation into endogenous proteins.

Main Results:

  • Successful delivery of exogenous ubiquitin into the cytosol of human cells.
  • Demonstration of functional incorporation of delivered ubiquitin into endogenous proteins.
  • Enhanced cytosolic access and functional integration achieved with L17ER4 peptide.

Conclusions:

  • The developed protein delivery strategy enables the study of exogenous ubiquitin in human cells.
  • This method facilitates the investigation of ubiquitin biology and semisynthetic ubiquitin variants.
  • The findings offer a new tool to advance understanding of protein homeostasis and degradation pathways.