The dynamic turnover of cellular proteins has been recognized for a long time, but the biochemical mechanisms which carry out the selective degradation of intracellular proteins have begun to be elucidated only recently. A major part of selective protein breakdown appears to be carried out by the ubiquitin proteolytic pathway. Studies indicated that the covalent conjugation of the polypeptide ubiquitin to proteins is the initial signal event in protein breakdown. We have characterized several enzymatic steps in the formation and breakdown of ubiquitin-protein conjugates, but major questions concerning the mode of action of the ubiquitin proteolytic pathway remained obscure. We intend to delineate some of the as yet unexplored enzymatic reactions in the formation and breakdown of ubiquitin conjugates. We wish to focus on the question: What determines the specificity of the ubiquitin conjugation system for the commitment of a certain protein for degradation. Recent results indicate that the availability of a free and exposed NH2-terminal Alpha-NH2 group of the protein substrate is an important determinant. We shall characterize the structure of different ubiquitin-protein conjugates to determine whether ubiquitin conjugation to the Alpha-NH2 group is the initial event which allows the subsequent conjugation of multiple molecules of ubiquitin to Epsilon-NH2 groups of lysine residues. We shall examine what other features of protein structure (besides the free NH2-terminus) are recognized by the uniquitin conjugation system. The selectivity of protein breakdown may further be increased by a correction system, which removes ubiquitin from incorrectly conjugated proteins not destined for degradation. We shall examine the possible role of ubiquitin-protein lyases in such a correction mechanism, in an assay system coupled to purified conjugate-forming enzymes. Since protein breakdown carries out important cellular functions, such as the regulation of enzyme levels and the removal of abnormal proteins, the elucidation of its mechanisms and selectivity are of basic importance and may have further implications in the understanding of diseases of abnormal protein catabolism.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK025614-08
Application #
3227507
Study Section
Biochemistry Study Section (BIO)
Project Start
1980-02-01
Project End
1989-01-31
Budget Start
1987-02-01
Budget End
1988-01-31
Support Year
8
Fiscal Year
1987
Total Cost
Indirect Cost
Name
Technion-Israel Institute of Technology
Department
Type
DUNS #
City
Haifa
State
Country
Israel
Zip Code
32000
Lahav-Baratz, S; Sudakin, V; Ruderman, J V et al. (1995) Reversible phosphorylation controls the activity of cyclosome-associated cyclin-ubiquitin ligase. Proc Natl Acad Sci U S A 92:9303-7
Sudakin, V; Ganoth, D; Dahan, A et al. (1995) The cyclosome, a large complex containing cyclin-selective ubiquitin ligase activity, targets cyclins for destruction at the end of mitosis. Mol Biol Cell 6:185-97
Hershko, A; Ganoth, D; Sudakin, V et al. (1994) Components of a system that ligates cyclin to ubiquitin and their regulation by the protein kinase cdc2. J Biol Chem 269:4940-6
Eytan, E; Armon, T; Heller, H et al. (1993) Ubiquitin C-terminal hydrolase activity associated with the 26 S protease complex. J Biol Chem 268:4668-74
Hershko, A; Ciechanover, A (1992) The ubiquitin system for protein degradation. Annu Rev Biochem 61:761-807
Hadari, T; Warms, J V; Rose, I A et al. (1992) A ubiquitin C-terminal isopeptidase that acts on polyubiquitin chains. Role in protein degradation. J Biol Chem 267:719-27
Hershko, A; Ganoth, D; Pehrson, J et al. (1991) Methylated ubiquitin inhibits cyclin degradation in clam embryo extracts. J Biol Chem 266:16376-9
Hershko, A (1991) The ubiquitin pathway for protein degradation. Trends Biochem Sci 16:265-8
Armon, T; Ganoth, D; Hershko, A (1990) Assembly of the 26 S complex that degrades proteins ligated to ubiquitin is accompanied by the formation of ATPase activity. J Biol Chem 265:20723-6
Heller, H; Hershko, A (1990) A ubiquitin-protein ligase specific for type III protein substrates. J Biol Chem 265:6532-5

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