Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:6.3.2.19 (ubiquitin-protein ligase)
 799 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Previous studies have shown that the activity of the ubiquitin-mediated proteolytic system declines markedly following reticulocyte maturation, but the specific alterations responsible for this phenomenon have not been defined. We find that the rate of ATP-dependent degradation of 125I-albumin is reduced 20-fold in lysates of rabbit erythrocytes, as compared to reticulocyte lysates. The activity of the proteolytic system in erythrocyte extracts can be restored by supplementation with components of the ubiquitin-protein ligase system purified from reticulocytes by affinity chromatography. These components are the ubiquitin-carrier protein E2, the activity of which is nearly completely absent, and the ligase E3, the activity of which is partially reduced in erythrocytes. Erythrocyte extracts contain other ligases which attach a single, or a few ubiquitin molecules to proteins; these products are different from the multi-ubiquitin derivatives which are formed by the ligase system of protein breakdown. Mature red cells may thus serve to distinguish between different ubiquitin-protein ligase systems with presumably different functions.
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PMID:Alterations in components of the ubiquitin-protein ligase system following maturation of reticulocytes to erythrocytes. 359 63

By affinity chromatography of a crude reticulocyte extract on ubiquitin-Sepharose, three enzymes required for the conjugation of ubiquitin with proteins have been isolated. One is the ubiquitin-activating enzyme (E1), which is covalently linked to the affinity column in the presence of ATP and can be specifically eluted with AMP and pyrophosphate (Ciechanover, A., Elias, S., Heller, H., and Hershko, A. (1982) J. Biol. Chem. 257, 2537-2542). A second enzyme, designated E2, is bound to the ubiquitin column when E1 and ATP are present, and is eluted with a thiol compound at high concentration. The third enzyme, designated E3, is adsorbed to the affinity column by noncovalent interactions and can be eluted with high salt or increased pH. The presence of all three enzymes is absolutely required for the conjugation of 125I-ubiquitin with proteins. All three affinity-purified enzymes are also required for the breakdown of 125I-albumin to acid-soluble material in the presence of ubiquitin, ATP, and the unadsorbed fraction of the affinity column. The following observations indicate that the function of E2 is the transfer of activated ubiquitin to the site of conjugation in the form of an E2-ubiquitin thiol ester intermediate. (a) E2 is rapidly inactivated by iodoacetamide, but can be protected against inactivation by a prior incubation with E1, ATP, and ubiquitin. This suggests an E1-mediated transfer of activated ubiquitin to an iodoacetamide-sensitive thiol site of E2. (b) The requirements for the binding of E2 to the ubiquitin column and the mode of its elution, cited above, are consistent with the notion that a covalent linkage is formed between E2 and Sepharose-bound ubiquitin. (c) Upon the incubation of 125I-ubiquitin with E1 and ATP, followed by the addition of purified E2, activated ubiquitin is transferred from E1 to several low molecular weight forms of E2, as analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The linkage of ubiquitin to all these forms has the characteristics of a thiol ester bond. In a further incubation with E3 and a protein substrate for conjugation, activated ubiquitin was transferred from the different forms of E2-ubiquitin to stable ubiquitin-protein conjugates. Thus, E3 is involved in the last step of the ligase system.
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PMID:Components of ubiquitin-protein ligase system. Resolution, affinity purification, and role in protein breakdown. 630 78

Abraxane, an FDA-approved albumin-bound nanoparticle (NP) form of paclitaxel (PTX) to treat breast cancer and nonsmall cell lung cancer (NSCLC), has been demonstrated to be more effective than the original Taxol, the single molecule form. We have established a cell line from NSCLC A549 cells to be resistant to Abraxane. To further understand the molecular mechanisms involved in the NP drug resistance, global protein expression profiles of Abraxane sensitive (A549) and resistant cells (A549/Abr), along with the treatment of Abraxane, have been obtained by a quantitative proteomic approach. The most significantly differentially expressed proteins are associated with lipid metabolism, cell cycle, cytoskeleton, apoptosis pathways and processes, suggesting several mechanisms are working synergistically in A549 Abraxane-resistant cells. Overexpression of proteins in the lipid metabolism processes, such as E3 ubiquitin-protein ligase RNF139 (RNF139) and Hydroxymethylglutaryl-CoA synthase (HMGCS1), have not been reported previously in the study of paclitaxel resistance, suggesting possibly different mechanism between nanoparticle and single molecular drug resistance. In particular, RNF139 is one of the most up-regulated proteins in A549 Abraxane-resistant cell line, but remains no change when the resistant cells were further treated with Abraxane and down-regulated in the sensitive cells after 4 h treatment of Abraxane. This study shows the use of a proteomic strategy to understand the unique response of drug resistant cells to a nanoparticle therapeutic.
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PMID:Quantitative Proteomic Analysis of Cellular Resistance to the Nanoparticle Abraxane. 2632 59