E1/E2/E3 Enzyme

E1, E2, and E3 enzymes are integral components of the ubiquitination pathway, a critical cellular process responsible for tagging proteins with ubiquitin to signal their degradation via the proteasome system. The E1 enzyme (ubiquitin-activating enzyme) initiates the process by activating ubiquitin in an ATP-dependent manner. The activated ubiquitin is then transferred to the E2 enzyme (ubiquitin-conjugating enzyme), which collaborates with an E3 enzyme (ubiquitin ligase) to specifically attach ubiquitin to target proteins. This specificity is primarily determined by the E3 ligase, which recognizes particular protein substrates. This system regulates various cellular functions, including protein turnover, cell cycle progression, and stress response, highlighting its importance in maintaining cellular homeostasis.