Fig. 1

The ubiquitination process. E1 hydrolyzes adenosine triphosphate (ATP) to catalyze the C-terminal acyl adenylation of ubiquitin. Then, ubiquitin is transferred to the cysteine residue of E1 active site, accompanied by the adenylation of the second ubiquitin. The adenylated ubiquitin is then transferred to the cysteine residue of the ubiquitin conjugated domain of E2. The final step in the binding of ubiquitin to the target is mediated by E3 ubiquitin ligase. The ubiquitinated proteins are then recognized and degraded by the proteasome. Ubiquitinated proteins can also be deubiquitinated by deubiquitin enzyme (DUBs)