UBC

Function

Ubiquitin

Exists either covalently attached to another protein, or free (unanchored). When covalently bound, it is conjugated to target proteins via an isopeptide bond either as a monomer (monoubiquitin), a polymer linked via different Lys residues of the ubiquitin (polyubiquitin chains) or a linear polymer linked via the initiator Met of the ubiquitin (linear polyubiquitin chains). Polyubiquitin chains, when attached to a target protein, have different functions depending on the Lys residue of the ubiquitin that is linked: Lys-6-linked may be involved in DNA repair; Lys-11-linked is involved in ERAD (endoplasmic reticulum-associated degradation) and in cell-cycle regulation; Lys-29-linked is involved in lysosomal degradation; Lys-33-linked is involved in kinase modification; Lys-48-linked is involved in protein degradation via the proteasome; Lys-63-linked is involved in endocytosis, DNA-damage responses as well as in signaling processes leading to activation of the transcription factor NF-kappa-B. Linear polymer chains formed via attachment by the initiator Met lead to cell signaling. Ubiquitin is usually conjugated to Lys residues of target proteins, however, in rare cases, conjugation to Cys or Ser residues has been observed. When polyubiquitin is free (unanchored-polyubiquitin), it also has distinct roles, such as in activation of protein kinases, and in signaling.

Post-translational modifications

Ubiquitin

Phosphorylated at Ser-65 by PINK1 during mitophagy. Phosphorylated ubiquitin specifically binds and activates parkin (PRKN), triggering mitophagy (PubMed:24660806, PubMed:24751536, PubMed:24784582, PubMed:25527291). Phosphorylation does not affect E1-mediated E2 charging of ubiquitin but affects discharging of E2 enzymes to form polyubiquitin chains. It also affects deubiquitination by deubiquitinase enzymes such as USP30 (PubMed:25527291).

Ubiquitin

Mono-ADP-ribosylated at the C-terminus by PARP9, a component of the PPAR9-DTX3L complex. ADP-ribosylation requires processing by E1 and E2 enzymes and prevents ubiquitin conjugation to substrates such as histones.

Sequence similarities

Belongs to the ubiquitin family.

Cellular localization

• Ubiquitin
• Cytoplasm
• Nucleus

Alternative names

• Polyubiquitin-C
• UBC

Database links

• entrezGene:7316
• entrezGene:7314
• omim:191340
• omim:191339
• swissprot:P0CG48
• swissprot:P0CG47
• swissprot:P62979
• swissprot:P62987
• swissprot:P0CG47
• swissprot:P62988

Target type

Proteins

Primary research area

Neuroscience

Molecular weight

77039Da