E3 ubiquitin-protein ligase (E3 ligase)

E3 ubiquitin-protein ligases are a large and diverse family of enzymes that play a pivotal role in the ubiquitin-proteasome system (UPS). They are responsible for the final step of the ubiquitination cascade, where they facilitate the transfer of ubiquitin from an E2 conjugating enzyme to a specific substrate protein. This modification typically marks the substrate for degradation by the 26S proteasome, although it can also regulate protein localization, activity, and interactions. In humans, there are over 600 E3 ligases, categorized into three main types based on their structural domains: RING (Really Interesting New Gene), HECT (Homologous to E6AP Carboxyl Terminus), and RBR (RING-Between-RING). Because they determine substrate specificity, E3 ligases are highly attractive therapeutic targets for diseases characterized by protein dysregulation, such as cancer and neurodegeneration. Pharmacological modulation of E3 ligases includes direct inhibition (e.g., MDM2 inhibitors), molecular glues that redirect ligase activity toward new substrates (e.g., IMiDs targeting Cereblon), and Proteolysis Targeting Chimeras (PROTACs) that hijack E3 ligases to degrade specific proteins of interest.

Other names

Ubiquitin-protein ligaseE3 enzymeUbiquitin ligase

E3 ubiquitin-protein ligases are targeted through several mechanisms: direct inhibition of the ligase's enzymatic activity or its interaction with a substrate (e.g., MDM2-p53 inhibitors), molecular glues that induce the recruitment of neosubstrates (e.g., IMiDs targeting Cereblon), and Proteolysis Targeting Chimeras (PROTACs) that utilize a bifunctional molecule to recruit an E3 ligase to a specific protein of interest for degradation.