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. 2023 Oct 2;55(10):2097–2104. doi: 10.1038/s12276-023-01087-w

Fig. 1. The ubiquitin proteasome system and classification of E3 ubiquitin ligases.

Fig. 1

a Ubiquitination of proteins is achieved through an enzymatic cascade involving ubiquitin-activating enzyme (E1), ubiquitin-conjugating enzyme (E2) and ubiquitin ligase (E3). E3 ubiquitin ligases provide platforms for binding E3 enzymes and specific protein substrates, thereby coordinating ubiquitination of the target protein. b The HECT and RBR types transfer ubiquitin to its active site cysteine to form a thioester intermediate before transferring ubiquitin to the substrate protein. The RING type transfers ubiquitin directly from E2 to the substrate protein.