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The Proteasome

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

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.
In this pathway, the target proteins are first tagged with small proteins called ubiquitin. A series of enzymes carry out the ubiquitination of the target proteins - E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and E3...

The Proteasome

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.
In this pathway, the target proteins are first tagged with small proteins called ubiquitin. A series of enzymes carry out the ubiquitination of the target proteins - E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and E3...

The Proteasome Structure

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.
The proteasome is an...

Protein Complexes with Interchangeable Parts

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.
The SCF ubiquitin ligase is a protein complex of five individual proteins. This complex attaches ubiquitin to other target proteins to mark them for degradation. In order to...

Protein Complex Assembly

Protein Complex Assembly

Proteins can form homomeric complexes with another unit of the same protein or heteromeric complexes with different types. Most protein complexes self-assemble spontaneously via ordered pathways, while some proteins need assembly factors that guide their proper assembly. Despite the crowded intracellular environment, proteins usually interact with their correct partners and form functional complexes.
Many viruses self-assemble into a fully functional unit using the infected host cell to...

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Related Experiment Video

Updated: May 15, 2026

Examining Proteasome Assembly with Recombinant Archaeal Proteasomes and Nondenaturing PAGE: The Case for a Combined Approach

Examining Proteasome Assembly with Recombinant Archaeal Proteasomes and Nondenaturing PAGE: The Case for a Combined Approach

Published on: December 17, 2016

Formation of alternative proteasomes: same lady, different cap?

Elah Pick¹, Tali S Berman

¹Department of Biology and Environment, Faculty of Natural Sciences, University of Haifa at Oranim, Tivon 36006, Israel. elahpic@research.haifa.ac.il

|January 22, 2013

Summary

The 26S proteasome, a cellular complex, may have an alternative activation pathway in eukaryotes. This pathway involves p97 and the COP9 signalosome (CSN), forming a novel "alternative cap" for substrate elimination.

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Last Updated: May 15, 2026

Examining Proteasome Assembly with Recombinant Archaeal Proteasomes and Nondenaturing PAGE: The Case for a Combined Approach

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The Development and Application of Biophysical Assays for Evaluating Ternary Complex Formation Induced by Proteolysis Targeting Chimeras (PROTACS)

The Development and Application of Biophysical Assays for Evaluating Ternary Complex Formation Induced by Proteolysis Targeting Chimeras (PROTACS)

Published on: January 12, 2024

Area of Science:

Cellular Biology
Protein Degradation
Molecular Mechanisms

Background:

The 26S proteasome is a key cellular machine for protein degradation, typically composed of a 20S core and a 19S regulatory particle.
Recent studies suggest archaeal 20S proteasomes can be activated by a p97-related AAA+ ATPase complex, similar to the 19S particle.
The presence of p97 in eukaryotes raises questions about potential alternative proteasome activation mechanisms.

Purpose of the Study:

To investigate the potential role of p97 and the COP9 signalosome (CSN) in eukaryotic proteasome regulation.
To explore the hypothesis of an alternative proteasome activation complex in higher organisms.
To provide supporting data for a novel mechanism of substrate elimination.

Main Methods:

Comparative analysis of proteasome activation mechanisms across different organisms.
Biochemical assays to investigate the interaction and function of p97 and CSN with the 20S proteasome.
In vivo studies to assess the physiological relevance of the proposed alternative cap.

Main Results:

The study presents data supporting the interaction between p97 and CSN in the context of proteasome regulation.
Evidence suggests that p97 and CSN can form a functional complex, termed an "alternative cap".
This alternative cap is proposed to facilitate the targeted degradation of specific protein substrates.

Conclusions:

Eukaryotes may possess an alternative pathway for 26S proteasome activation involving p97 and CSN.
This p97-CSN complex acts as a promiscuous and potentially transient "alternative cap".
This mechanism allows for the prompt and precise elimination of particular substrates, expanding our understanding of protein homeostasis.