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. 2020 Feb 4;8:39. doi: 10.3389/fcell.2020.00039

FIGURE 1.

FIGURE 1

Mechanism of action of RING-, HECT- and RBR-type E3 ubiquitin ligases (A) Schematic representation of a RING-type ubiquitin E3 ligase. RING E3s bind both the E2-ubiquitin and the substrate to be ubiquitinated, so bringing them together allows direct conjugation of ubiquitin (Ub) on the substrate by the E2. A monomeric RING E3 ligase is shown for illustrative purposes. (B) Schematic representation of a HECT-type ubiquitin E3 ligase. Ubiquitin is transferred first to a cysteine (C) of the HECT domain through a thioester bond and then to the substrate. (C) Schematic representation of an RBR-type ubiquitin E3 ligase. Two RING domains are separated by an in-between-RING (IBR) domain. Ubiquitin is first transferred to a cysteine (C) of the second RING domain through a thioester bond and then to the substrate.