Molecular shredders: how proteasomes fulfill their role.

The 20S proteasome is a large, cylinder-shaped protease that is found in all domains of life and plays a crucial role in cellular protein turnover. It has multiple catalytic centers located within the hollow cavity of a molecular cage. This architecture prevents unwanted degradation of endogenous proteins and promotes processive degradation of substrates by restricting the dissociation of partially digested polypeptides. Although this kind of self-compartmentalization is generally conserved, the proteasomes of bacteria, archaea and eukaryotes show many differences in architecture, subunit composition and regulation. The structure of the 20S proteasome and its inherent role in the regulation of proteasome function are gradually being elucidated.