ubiquitin-protein transferase activity

Definition

Target type: molecularfunction

Catalysis of the transfer of ubiquitin from one protein to another via the reaction X-Ub + Y = Y-Ub + X, where both X-Ub and Y-Ub are covalent linkages. [GOC:BioGRID, GOC:jh2, PMID:9635407]

Ubiquitin-protein transferase (E3 ligase) activity is a crucial molecular function that plays a central role in regulating diverse cellular processes. E3 ligases facilitate the attachment of ubiquitin, a small protein, to target proteins. This process, known as ubiquitination, is highly specific and can lead to a variety of downstream effects, including protein degradation, signal transduction, DNA repair, and protein trafficking. The ubiquitination cascade involves a series of enzymatic steps. First, ubiquitin is activated by a ubiquitin-activating enzyme (E1), which utilizes ATP to attach ubiquitin to itself. Next, the activated ubiquitin is transferred to a ubiquitin-conjugating enzyme (E2). Finally, the E3 ligase, through its substrate-binding domain, recognizes and interacts with a specific target protein, and then transfers the ubiquitin from the E2 to the target protein. E3 ligases exhibit remarkable diversity in their substrate specificity, ensuring precise regulation of cellular processes. They employ various mechanisms to target their substrates, including direct interaction with specific amino acid sequences, recognition of protein modifications like phosphorylation, and association with protein complexes. The ubiquitin molecule can be attached to target proteins as a single unit (monoubiquitination) or as a polyubiquitin chain (polyubiquitination). The linkage between ubiquitin molecules within a polyubiquitin chain can vary, and different linkages are associated with distinct cellular outcomes. For example, K48-linked polyubiquitin chains typically target proteins for degradation by the proteasome, while K63-linked polyubiquitin chains are often involved in signal transduction pathways. The ubiquitination system is highly dynamic and reversible, with deubiquitinating enzymes (DUBs) acting as counter-regulators. DUBs remove ubiquitin chains from target proteins, thus reversing the effects of ubiquitination. The intricate interplay between E3 ligases and DUBs ensures precise control of ubiquitination levels, allowing for fine-tuning of cellular processes.'
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Proteins (23)

Compounds (50)