title: Orchestra for assembly and fate of polyubiquitin chains.
abstract: Selective protein degradation by the 26 S proteasome usually requires a polyubiquitin chain attached to the protein substrate by three classes of enzymes: a ubiquitin-activating enzyme (E1), a ubiquitin-conjugating enzyme (E2), and a ubiquitin ligase (E3). This reaction can produce different polyubiquitin chains that, depending on size and linkage type, can provide distinct intracellular signals. Interestingly, polyubiquitination is sometimes regulated by additional conjugation factors, called E4s (polyubiquitin chain conjugation factors). Yeast UFD2 (ubiquitin fusion degradation protein-2), the first E4 to be described, binds to the ubiquitin moieties of preformed conjugates and catalyses ubiquitin-chain elongation together with E1, E2, and E3. Recent studies have illustrated that the E4 enzyme UFD2 co-operates with an orchestra of ubiquitin-binding factors in an escort pathway to transfer and deliver polyubiquitinated substrates to the 26 S proteasome. Here we propose a model in which E4-dependent polyubiquitination pathways are modulated by different ubiquitin-binding proteins, using ataxin-3 as an example.
authors.affiliation: Centre for Molecular Neurobiology (ZMNH), University of Hamburg, Falkenried 94, 20251 Hamburg, Germany.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Kuhlbrodt
authors.forename: Julien
authors.initials: J
authors.lastname: Mouysset
authors.forename: Thorsten
authors.initials: T
authors.lastname: Hoppe
mesh_terms: D000818:Animals; D000067699:Ataxin-3; D006801:Humans; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009687:Nuclear Proteins; D025821:Polyubiquitin / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D012097:Repressor Proteins; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D044764:Ubiquitin-Activating Enzymes / Q000378:metabolism*; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*
chemical_list: D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D025821:Polyubiquitin; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; C092341:ATXN3 protein, human; D000067699:Ataxin-3; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; D044764:Ubiquitin-Activating Enzymes; C114683:UFD2 protein, S cerevisiae