Figure 2.

The molecular players of the Ub-conjugation system. Ubiquitination is a three-step enzyme-catalyzed reaction coordinated by E1 or Ub-activating enzyme that catalyzes the ATP and Mg²⁺ dependent activation of Ub required to form a thioester bond in between catalytic cysteine on the E1 and C terminus glycine of Ub. The transfer of activated Ub from the Ub-conjugating enzyme (E2) to the substrate is mediated by the E3-Ub ligase. The removal and recycling of Ub from substrates are catalyzed by DUBs which maintain the Ub-pool. S, substrate; Ub, ubiquitin; DUB, deubiquitinase.