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Definition: What is the proteasome and its function in protein degradation?

The proteasome is a large protein complex found in cells that plays a crucial role in protein degradation. It acts as a cellular garbage disposal system, breaking down unwanted or damaged proteins into smaller peptides. This process is essential for maintaining cellular homeostasis and regulating various cellular processes.

Structure of the Proteasome

The proteasome is composed of multiple subunits that come together to form a cylindrical structure. It consists of a central core particle (CP) and one or two regulatory particles (RP). The CP is responsible for the actual degradation of proteins, while the RP helps in recognizing and delivering specific proteins to the CP.

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The CP is made up of four stacked rings, each containing seven individual subunits. The two outer rings consist of α-subunits, which provide structural stability, while the two inner rings contain β-subunits, which possess proteolytic activity. The β-subunits have three distinct types: β1, β2, and β5, each with different substrate specificities.

The RP is attached to one or both ends of the CP and consists of multiple subunits. It acts as a gatekeeper, controlling the entry of proteins into the proteasome for degradation. The RP recognizes proteins that are tagged with specific degradation signals, such as ubiquitin, and facilitates their binding to the CP.

Function of the Proteasome in Protein Degradation

The proteasome plays a crucial role in maintaining protein homeostasis by selectively degrading proteins that are no longer needed or are misfolded, damaged, or abnormal. This process, known as proteolysis, ensures the removal of unwanted proteins and prevents their accumulation, which can be detrimental to cellular function.

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Protein degradation by the proteasome is a tightly regulated process. Proteins that need to be degraded are tagged with a small protein called ubiquitin. This tagging process, known as ubiquitination, marks the protein for recognition and subsequent degradation by the proteasome.

Once a protein is ubiquitinated, it is recognized by the RP of the proteasome. The RP unfolds the protein and guides it into the central chamber of the CP. Within the CP, the β-subunits of the proteasome cleave the protein into smaller peptides. These peptides are then further processed by other cellular enzymes and recycled for the synthesis of new proteins.

The proteasome also plays a role in regulating various cellular processes by selectively degrading specific proteins involved in cell cycle progression, DNA repair, immune response, and signal transduction. By controlling the levels of these regulatory proteins, the proteasome helps maintain cellular homeostasis and ensures proper functioning of the cell.

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In summary, the proteasome is a large protein complex that acts as a cellular garbage disposal system, degrading unwanted or damaged proteins. It plays a crucial role in maintaining protein homeostasis, regulating cellular processes, and preventing the accumulation of harmful proteins.

Keywords: proteasome, protein, proteins, cellular, degradation, subunits, process, homeostasis, function