Figure 1.

Protein ubiquitin proteasomal degradation and deubiquitination. A protein destined for degradation unleashes a cascade of enzymatic activity involving ubiquitination and proteasomal degradation. E1 Ub-activating enzymes activate ubiquitin and pass the ubiquitin to E2-Ub-conjugating enzymes. E3 Ub-ligases recognize the protein substrates and couple E2-Ub-conjugating enzymes to covalently add the ubiquitin or ubiquitin moieties to the protein substrates. The ubiquitinated proteins are then degraded by the proteasome. Deubiquitinating enzymes remove the mono-ubiquitin or polyubiquitin chains from the ubiquitinated protein to stabilize the protein from proteasomal degradation and recycle ubiquitin units. Ub: ubiquitin; E1: E1 Ub-activating enzyme; E2: E2-Ub-conjugating enzyme, E3: E3 Ub-ligases; DUB: deubiquitinating enzyme.