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Ubiquitin ligase

Synonym: E3 ubiquitin ligase
German: E3-Enzym

1 Definition

Ubiquitin ligases are a class of enzymes that transfer ubiquitin to target proteins during the process of ubiquitination. Ubiquitin ligases are part of an enzyme cascade after ubiquitin-activating enzymes (E1 enzymes) and ubiquitin-conjugating enzymes (E2 enzymes).

2 Biochemistry

In a step requiring ATP, ubiquitin is activated by E1 enzymes and subsequently transferred to E2 enzymes. E3 ubiquitin ligase first makes sure that ubiquitin-loaded E2 enzymes reach their intended substrate and subsequently catalyzes the binding of ubiquitin to that substrate. This is achieved by creating an isopeptide bond between the C-terminal glycine of the ubiquitin and an ε-amino group of an internal lysine of the substrate.

Compared to E1 and E2 enzymes, E3 ubiquitin ligases are a very big class of enzymes with several hundred members. They can be divided into three groups by whether of not they have a RING, HECT, or RBR domain.

3 References

  • Ye et al Building ubiquitin chains: E2 enzymes at work. Nat Rev Mol Cell Biol; 2009
  • Chaugule et al Specificity and disease in the ubiquitin system. Biochem Soc Trans; 2016

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