Ubiquitinconjugated

Ubiquitin-conjugated describes a molecule, typically a substrate protein, that has covalently attached ubiquitin as part of the ubiquitination process. Ubiquitin is a small, 76-amino-acid protein attached to substrate lysines via an isopeptide bond between the ubiquitin C-terminus and the substrate’s lysine residue. The conjugation is carried out by a three-enzyme cascade: an E1 activating enzyme transfers ubiquitin to an E2 conjugating enzyme, and an E3 ligase provides substrate specificity to attach ubiquitin to the target.

A substrate may carry a single ubiquitin (monoubiquitination) or a chain of ubiquitin molecules (polyubiquitination). The outcome of ubiquitination depends on the linkage type between ubiquitin units and the number of attached ubiquitin moieties. For example, Lys48-linked polyubiquitin commonly marks proteins for proteasomal degradation, whereas Lys63-linked chains participate in signaling, DNA repair, endocytosis, and autophagy. Other linkages and mixed chains convey diverse regulatory signals. Monoubiquitination can regulate activity, localization, or interactions without triggering degradation.

Deubiquitinating enzymes (DUBs) reverse ubiquitination by cleaving the isopeptide bonds, thereby removing ubiquitin and restoring substrates or regenerating ubiquitin pools. Ubiquitin-conjugated substrates are recognized by the proteasome or by ubiquitin-binding domains that recruit downstream factors, influencing degradation, trafficking, or signaling.

Detection and study employ techniques such as immunoblotting with anti-ubiquitin antibodies, immunoprecipitation under denaturing conditions, ubiquitin linkage-specific antibodies, affinity reagents like TUBEs, and mass spectrometry to identify modified residues and chain types.

Dysregulation of ubiquitination is linked to diseases including cancer, neurodegenerative disorders, and immune dysfunction. The term ubiquitin-conjugated serves as a descriptive label for substrates modified by ubiquitin, with the cellular outcome determined by chain length, linkage, site, and context.