20SKernpartikel

20SKernpartikel, in German literature also referred to as the 20S-Kernpartikel or 20S core particle, is the proteolytic core of the proteasome, a large multisubunit protease complex essential for regulated protein degradation in eukaryotic cells and archaea. The 20S Kernpartikel forms the catalytic center of the 26S proteasome, which degrades ubiquitin-tagged substrates when associated with regulatory particles.

Structurally, the 20SKernpartikel consists of four stacked heptameric rings, arranged as α7–β7–β7–α7, for a total of 28 subunits. The outer alpha rings regulate substrate entry, while the inner beta rings harbor the proteolytic active sites. In most eukaryotes, three beta subunits (β1, β2, β5) provide distinct proteolytic activities: caspase-like, trypsin-like, and chymotrypsin-like. Activation involves maturation of propeptides and removal of N-terminal residues.

Functionally, the 20SKernpartikel degrades unwanted or damaged proteins, contributing to protein quality control, cell cycle regulation, and antigen processing. In the presence of regulatory particles such as the 19S, it forms the 26S proteasome, which recognizes ubiquitin-tagged substrates. The 20S core can also act independently on certain substrates in ubiquitin-independent pathways.

Clinical relevance centers on proteasome inhibitors that target the 20S core particle or the 26S holoenzyme, used in cancer therapy and under investigation for other diseases. The 20SKernpartikel is conserved across many organisms, reflecting its fundamental role in intracellular proteostasis.