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Related Concept Videos

Covalently Linked Protein Regulators02:04

Covalently Linked Protein Regulators

Proteins can undergo many types of post-translational modifications, often in response to changes in their environment. These modifications play an important role in the function and stability of these proteins. Covalently linked molecules include functional groups, such as methyl, acetyl, and phosphate groups, and also small proteins, such as ubiquitin. There are around 200 different types of covalent regulators that have been identified.
These groups modify specific amino acids in a protein.
Protein Complexes with Interchangeable Parts01:57

Protein Complexes with Interchangeable Parts

Groups of proteins may form a complex where each protein in this complex has a different role in the overall execution of the complex’s function. Often some of the proteins in the complex can be replaced by a closely related variant to give a complex that contains many of the same components yet is functionally distinct.
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The Proteasome02:18

The Proteasome

Eukaryotic cells can degrade proteins through several pathways. One of the most important amongst these is the ubiquitin-proteasome pathway. It helps the cell eliminate the misfolded, damaged, or unwarranted cytoplasmic proteins in a highly specific manner.
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Regulated Protein Degradation02:58

Regulated Protein Degradation

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.
Protein degradation plays two important roles in the cells. It helps to protect cells from misfolded or damaged proteins before they lead to a...
The Proteasome01:13

The Proteasome

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 (ubiquitin...
The Proteasome Structure01:17

The Proteasome Structure

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.
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Related Experiment Video

Updated: Jun 29, 2026

Ubiquitin Chain Analysis by Parallel Reaction Monitoring
08:33

Ubiquitin Chain Analysis by Parallel Reaction Monitoring

Published on: June 17, 2020

Distinct functional surface regions on ubiquitin.

K E Sloper-Mould1, J C Jemc, C M Pickart

  • 1Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, Illinois 60208, USA.

The Journal of Biological Chemistry
|June 16, 2001
PubMed
Summary

Ubiquitin targets proteins for degradation or endocytosis. Researchers identified key surface residues in ubiquitin essential for yeast growth, with specific sites crucial for endocytosis and proteasome degradation.

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Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • Ubiquitin is a highly conserved polypeptide crucial for protein regulation.
  • Its functions include targeting proteins for proteasome degradation and endocytosis.
  • Polyubiquitin chains signal for proteasome binding, while monoubiquitin mediates endocytosis.

Purpose of the Study:

  • To identify essential surface residues of ubiquitin in Saccharomyces cerevisiae.
  • To elucidate the roles of specific residues in ubiquitin's functions: proteasome degradation and endocytosis.
  • To understand the structural basis of ubiquitin signaling.

Main Methods:

  • Alanine scanning mutagenesis was employed to assess the importance of ubiquitin's surface residues.
  • Mutant yeast strains were analyzed for their vegetative growth.
  • Functional assays likely involved assessing protein degradation and endocytosis pathways.

Main Results:

  • Only 16 out of 63 surface residues of ubiquitin are essential for yeast vegetative growth.
  • Most essential residues cluster in hydrophobic regions involved in proteasome recognition and/or endocytosis.
  • Distinct functional surfaces were identified: residues around Phe(4) are critical for endocytosis, and those around Ile(44) are vital for both endocytosis and proteasome degradation.

Conclusions:

  • A small subset of ubiquitin surface residues is critical for its fundamental biological roles.
  • Specific residues and their spatial organization dictate ubiquitin's engagement with distinct cellular pathways.
  • This study provides insights into the structure-function relationship of ubiquitin in yeast.