title: In vivo disassembly of free polyubiquitin chains by yeast Ubp14 modulates rates of protein degradation by the proteasome.
abstract: Degradation of many eukaryotic proteins requires their prior ligation to polyubiquitin chains, which target substrates to the 26S proteasome, an abundant cellular protease. We describe a yeast deubiquitinating enzyme, Ubp14, that specifically disassembles unanchored ('free') ubiquitin chains in vitro, a specificity shared by mammalian isopeptidase T. Correspondingly, deletion of the UBP14 gene from yeast cells results in a striking accumulation of free ubiquitin chains, which correlates with defects in ubiquitin-dependent proteolysis. Increasing the steady-state levels of ubiquitin chains in wild-type cells (by expressing a derivative of ubiquitin with an altered C-terminus) inhibits protein degradation to a degree comparable with that observed in ubp14delta cells. Inhibition of degradation is also seen when an active site mutant of Ubp14 is overproduced in vivo. Surprisingly, overproduction of wild-type Ubp14 can inhibit degradation of some proteins as well. Finally, Ubp14 and human isopeptidase T are shown to be functional homologs by complementation analysis. We propose that Ubp14 and isopeptidase T facilitate proteolysis in vivo by preventing unanchored ubiquitin chains from competitively inhibiting polyubiquitin-substrate binding to the 26S proteasome.
authors.affiliation: University of Chicago, Department of Biochemistry and Molecular Biology, IL 60637, USA.
authors.lastname: Amerik AYu
authors.forename: S
authors.initials: S
authors.lastname: Swaminathan
authors.forename: B A
authors.initials: BA
authors.lastname: Krantz
authors.forename: K D
authors.initials: KD
authors.lastname: Wilkinson
authors.forename: M
authors.initials: M
authors.lastname: Hochstrasser
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D019759:Carbon-Nitrogen Lyases; D010450:Endopeptidases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D006801:Humans; D015151:Immunoblotting; D008190:Lyases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010447:Peptide Hydrolases / Q000737:chemistry / Q000378:metabolism*; D010641:Phenotype; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment; D013379:Substrate Specificity; D014452:Ubiquitins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D005656:Fungal Proteins; D029701:Saccharomyces cerevisiae Proteins; D014452:Ubiquitins; D010450:Endopeptidases; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; C108364:UBP14 protein, S cerevisiae; D008190:Lyases; D019759:Carbon-Nitrogen Lyases; C034300:isopeptidase