Polyubiquitin chain (PolyUb) (PolyUb)

Polyubiquitin chains are post-translational modifications consisting of ubiquitin monomers linked covalently to form polymers on intracellular substrate proteins. These chains serve as a sophisticated signaling language, often referred to as the "ubiquitin code," where the specific lysine residue used for linkage (e.g., K48, K63) determines the functional outcome for the substrate (Komander & Rape, 2012, Annu Rev Biochem) [1]. K48-linked chains typically target proteins for degradation by the 26S proteasome, a process essential for maintaining protein homeostasis and regulating the cell cycle (Pickart & Fushman, 2004, Curr Opin Chem Biol) [2]. In contrast, K63-linked chains often mediate non-degradative processes such as DNA repair, endocytosis, and scaffold formation in immune signaling pathways (Popovic et al., 2014, BMC Biol) [3]. From a therapeutic perspective, these chains are central to the mechanism of proteasome inhibitors used in multiple myeloma and are the intended "tag" in targeted protein degradation (TPD) modalities like PROTACs and molecular glues (Deshaies, 2015, Nat Chem Biol) [4]. Modern drug discovery also targets the enzymes that assemble (E3 ligases) or disassemble (deubiquitinases) these chains to modulate protein levels in various diseases (Moreau et al., 2020, Nat Rev Drug Discov) [5]. Dysfunction in the formation or recognition of these chains is implicated in a wide range of diseases, including various cancers and neurodegenerative disorders characterized by the accumulation of ubiquitinated protein aggregates (Zheng et al., 2016, Front Mol Neurosci) [6]. Consequently, polyubiquitin chains represent both a critical biological signal and a versatile handle for therapeutic intervention in precision medicine.

Other names

Ubiquitin chainUbiquitin polymerMulti-ubiquitin chainK48-linked ubiquitinK63-linked ubiquitinPolyubiquitin conjugate

Modulation of the ubiquitin-proteasome system via inhibition of the 26S proteasome, inhibition of deubiquitinating enzymes (DUBs), or recruitment of E3 ubiquitin ligases to induce neo-substrate ubiquitination (Targeted Protein Degradation) [3][4][5].