Ubiquitin (Ub)

Ubiquitin is a highly conserved small regulatory protein (76 amino acids, ~8.6 kDa) found in all eukaryotic cells[1][6]. It mediates post-translational modification of numerous proteins via a process known as ubiquitylation, in which ubiquitin is covalently attached to lysine residues on substrate proteins[1][5]. This modification is central to protein homeostasis, marking proteins for degradation by the 26S proteasome, altering cellular localization, modulating activity, and regulating interactions[1][3]. Ubiquitin is itself encoded by several genes (UBB, UBC, UBA52, RPS27A), and its conjugation/deconjugation requires a cascade of E1 activating, E2 conjugating, and E3 ligase enzymes[1][5]. The ubiquitin–proteasome system is fundamental to the regulation of many cellular processes, including cell cycle progression, signal transduction, DNA repair, immune response, and apoptosis[3]. Dysregulation of ubiquitin pathways has roles in cancer, neurodegenerative disorders, cardiovascular disease, and infection[3]. Drugs do not target ubiquitin directly due to its essentiality, but several drugs (such as bortezomib) inhibit the proteasome, disrupting the downstream consequences of ubiquitylation for therapeutic benefit in certain cancers[3]. Notes and rationale: - Ubiquitin is not considered a classic "drug target" such as a receptor, enzyme, or transporter: it is a post-translational modifier, not a druggable protein on its own. Drug discovery focuses on components of the ubiquitin pathway (e.g., E1, E2, E3 enzymes, proteasome) rather than ubiquitin itself[3]. - Ubiquitin as a search term for drug-target purposes is incorrect (is_incorrect: true) because therapeutic interventions modulate its pathway rather than ubiquitin protein directly. - Interacting drugs listed for the ubiquitin–proteasome pathway (such as bortezomib) target the proteasome; there are no approved drugs that act directly on ubiquitin[3]. - As a biomarker, increased ubiquitin conjugates can signal impaired proteasome activity or stress states. - Systemic targeting of ubiquitin is profoundly toxic due to its central cellular functions. For structured target-centric drug discovery, it is more appropriate to search for enzymes within the ubiquitin-proteasome system, such as "26S proteasome", "Ubiquitin-activating enzyme E1", "Ubiquitin ligase (E3)", etc., rather than ubiquitin itself[3].

Other names

Ubiquitous immunopoietic polypeptideUbbUb

Not applicable for drugs against ubiquitin; drugs target the ubiquitin-proteasome pathway (e.g., proteasome inhibitors)