Proteasome
Protein complexes that degrade proteins via proteolysis.
Proteasomes are essential protein complexes responsible for the degradation of proteins by proteolysis, a chemical reaction that breaks peptide bonds. They are found inside all eukaryotes and archaea, and in some bacteria. In eukaryotes, proteasomes are located both in the nucleus and in the cytoplasm. The proteasomal degradation pathway is essential for many cellular processes, including the cell cycle, the regulation of gene expression, and responses to oxidative stress.
- type
- Protein complex
- location
- Eukaryotes, archaea, some bacteria
- subcellular location
- Nucleus and cytoplasm (in eukaryotes)
- core complex
- 20S proteasome
- full complex
- 26S proteasome (20S core + 19S regulatory particle)
- function
- Degradation of proteins via proteolysis
- key associated protein
- Ubiquitin
Lore & Background
Before the discovery of the ubiquitin–proteasome system, protein degradation in cells was thought to rely mainly on lysosomes. However, work by Joseph Etlinger and Alfred L. Later work on modification of histones led to the identification of an unexpected covalent modification of the histone protein by ubiquitin, a protein that had no known function. It was then discovered that a previously identified protein associated with proteolytic degradation, known as ATP-dependent proteolysis factor 1 (APF-1), was the same protein as ubiquitin. The proteolytic activities of this system were isolated as a multi-protein complex originally called the multi-catalytic proteinase complex by Sherwin Wilk and Marion Orlowski. Later, the ATP-dependent proteolytic complex responsible for ubiquitin-dependent protein degradation was discovered and called the 26S proteasome.
Reader's Guide
The proteasome is a central component of the ubiquitin-proteasome system, a major mechanism by which cells regulate the concentration of particular proteins and degrade misfolded proteins. Much of the early work leading up to the discovery occurred in the late 1970s and early 1980s at the Technion in the laboratory of Avram Hershko, where Aaron Ciechanover worked as a graduate student. Hershko's year-long sabbatical in the laboratory of Irwin Rose at the Fox Chase Cancer Center provided key conceptual insights. The degradation process by the proteasome yields peptides of about seven to eight amino acids long, which can then be further degraded into shorter amino acid sequences and used in synthesizing new proteins. Cryo-electron tomography has provided unique insight into proteasomes within cells, showing that in neurons, most proteasomes were in a ground state, ready to start working when a cell undergoes proteotoxic stress.
Did You Know?
- Proteasomes are found inside all eukaryotes and archaea, and in some bacteria.
- The core 20S proteasome is a cylindrical complex of four stacked rings forming a central pore.
- Proteins destined for degradation by the 26S proteasome require attachment of ubiquitin and an unstructured region of about 25 amino acids.
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