title: Surface hydrophobic residues of multiubiquitin chains essential for proteolytic targeting.
abstract: Ubiquitin conjugation is a signal for degradation of eukaryotic proteins by the 26S protease. Conjugation of a homopolymeric multiubiquitin chain to a substrate lysine residue results in 10-fold faster degradation than does conjugation of monoubiquitin, but the molecular basis of enhanced targeting by chains is unknown. We show that ubiquitin residues L8, I44, and V70 are critical for targeting. Mutation of pairs of these residues to alanine had little effect on attachment of ubiquitin to substrates but severely inhibited degradation of the resulting conjugates. The same mutations blocked the binding of chains to a specific subunit (S5a) of the regulatory complex of the 26S protease. The side chains implicated in this binding--L8, I44, and V70--form repeating patches on the chain surface. Thus, hydrophobic interactions between these patches and S5a apparently contribute to enhanced proteolytic targeting by multiubiquitin chains.
authors.affiliation: Department of Biochemistry, School of Medicine and Biomedical Sciences, State University of New York, Buffalo 14214, USA.
authors.forename: R
authors.initials: R
authors.lastname: Beal
authors.forename: Q
authors.initials: Q
authors.lastname: Deveraux
authors.forename: G
authors.initials: G
authors.lastname: Xia
authors.forename: M
authors.initials: M
authors.lastname: Rechsteiner
authors.forename: C
authors.initials: C
authors.lastname: Pickart
mesh_terms: D001704:Biopolymers / Q000235:genetics / Q000378:metabolism*; D004252:DNA Mutational Analysis; D008025:Ligases / Q000378:metabolism; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D010447:Peptide Hydrolases / Q000378:metabolism*; D025821:Polyubiquitin; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D013379:Substrate Specificity; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins / Q000235:genetics / Q000378:metabolism*
chemical_list: D001704:Biopolymers; D014452:Ubiquitins; D025821:Polyubiquitin; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; D008025:Ligases