Ubiquitin functions primarily through a process known as ubiquitination, where it attaches to a substrate protein, marking it for various fates. The most well-known outcome is the degradation of the substrate protein by the proteasome, a large protein complex responsible for breaking down unneeded or damaged proteins. Ubiquitination involves a cascade of enzymatic activities, typically executed by E1 (ubiquitin-activating enzymes), E2 (ubiquitin-conjugating enzymes), and E3 (ubiquitin ligases).
