a. 3 ubiquitin-ligases (E1, E2, E3) attach a ubiquitin polypeptide to a protein targeted for digestion.

b. The ubiquitinized protein binds to proteasome lid and enters central chamber where it is cleaved into peptides via tryptic,
chymotryptic, & caspace proteolytic activity. The ubiquitin is recycled.

c. Cytosolic peptidases further digest the degraded peptides.  BACK