The Proteasome

In eukaryotes, incorrectly folded proteins are degraded through pathways including the ubiquitin-proteasome pathway.

A ubiquitin ligase recognizes signals that show the difference between normal proteins those targeted for degradation. Several ubiquitin molecules are transferred to a specific amino acid on the target protein to mark them for degradation.

An ATP-dependent protease complex called the proteasome degrades these polyubiquitinated proteins in the proteolytic core surrounded by caps.

Deubiquitinase, an enzyme in the cap, cleaves ubiquitin from the substrate permitting the ubiquitin to be recycled.

The cap uses energy from ATP hydrolysis to unfold the target protein. With each round of ATP hydrolysis, the unfolded protein is fed into the core.

Here, it is digested by the proteases to form short peptides that are released into the cytosol, where peptidases further degrade them into their constituent amino acids for reuse.