proteasome §

A large muticatalytic protease. Typically composed of:

• A 20S catalytic core
• Two 19S regulatory caps, one at each end.

The association of the core and the caps requires ATP as well as the ATPase activity of many of the caps’ subunits.

After ubiquitination, the ubiquitin tagged chain is recognised by the 19S caps of the proteasome, which unfolds the tagged protein so it an be fed into the proteasome’s catalytic core. The protein chain is then degraded in the core into short peptides which are released by the opposite cap into the cytosol.

Evidence shows the proteasome is implicated in the production of peptides for MHC class I molecules. Whether it is the only cytosolic protease capable of generating peptides for transport into the ER is not known.

Adaptation of the catalytic core leads to immunoproteasome and thymoproteasome.