page_title: Proteasome
section_title: Protein degradation process
hierarchical_section_title: Proteasome / Protein degradation process
caption_attribution_description: Original description - Cartoon representation of ubiquitin protein, highlighting the secondary structure. α-helices are coloured in blue and the β-sheet in green. The normal attachment point for a further ubiquitin molecule in polyubiquitin chain formation, lysine 48, is shown in pink. Image was created using PyMOL
context_page_description: Proteasomes are protein complexes which degrade unneeded or damaged proteins by proteolysis, a chemical reaction that breaks peptide bonds. Enzymes that help such reactions are called proteases.
  Proteasomes are part of a major mechanism by which cells regulate the concentration of particular proteins and degrade misfolded proteins. Proteins are tagged for degradation with a small protein called ubiquitin. The tagging reaction is catalyzed by enzymes called ubiquitin ligases. Once a protein is tagged with a single ubiquitin molecule, this is a signal to other ligases to attach additional ubiquitin molecules. The result is a polyubiquitin chain that is bound by the proteasome, allowing it to degrade the tagged protein. The degradation process 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.
  Proteasomes are found inside all eukaryotes and archaea, and in some bacteria.
  In eukaryotes, proteasomes are located both in the nucleus and in the cytoplasm.
  In structure, the proteasome is a cylindrical complex containing a "core" of four stacked rings forming a central pore.
caption: Ribbon diagram of ubiquitin, the highly conserved protein that serves as a molecular tag targeting proteins for degradation by the proteasome
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