Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P62988 (Ubiquitin)
 4,326 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We tested the role of different intracellular proteolytic pathways in sepsis-induced muscle proteolysis. Sepsis was induced in rats by cecal ligation and puncture; controls were sham operated. Total and myofibrillar proteolysis was determined in incubated extensor digitorum longus muscles as release of tyrosine and 3-methylhistidine, respectively. Lysosomal proteolysis was assessed by using the lysosomotropic agents NH4Cl, chloroquine, leupeptin, and methylamine. Ca(2+)-dependent proteolysis was determined in the absence or presence of Ca2+ or by blocking the Ca(2+)-dependent proteases calpain I and II. Energy-dependent proteolysis was determined in muscles depleted of ATP by 2-deoxyglucose and 2.4-dinitrophenol. Muscle ubiquitin mRNA and the concentrations of free and conjugated ubiquitin were determined by Northern and Western blots, respectively, to assess the role of the ATP-ubiquitin-dependent proteolytic pathway. Total and myofibrillar protein breakdown was increased during sepsis by 50 and 440%, respectively. Lysosomal and Ca(2+)-dependent proteolysis was similar in control and septic rats. In contrast, energy-dependent total and myofibrillar protein breakdown was increased by 172% and more than fourfold, respectively, in septic muscle. Ubiquitin mRNA was increased severalfold in septic muscle. The results suggest that the increase in muscle proteolysis during sepsis is due to an increase in nonlysosomal energy-dependent protein breakdown, which may involve the ubiquitin system.
 ...
PMID:Sepsis stimulates nonlysosomal, energy-dependent proteolysis and increases ubiquitin mRNA levels in rat skeletal muscle. 798 81

The ATP-ubiquitin-dependent proteolytic pathway (ubiquitin pathway) is believed to be involved in the formation of various neuronal inclusion bodies including Lewy bodies (LBs), a pathological hallmark of Parkinson disease and diffuse Lewy body disease (DLBD). Since multicatalytic proteinase (MCP) is involved in the ubiquitin pathway, an investigation of whether MCP is involved in neuronal inclusion bodies would provide a clue to the mechanism underlying the formation of neuronal inclusion bodies as well as to the pathogenesis of degenerative neurological disorders. In this study, we investigated detailed immunolocalization of MCP in LBs in DLBD brains using light and electron microscopy. We raised three different monoclonal antibodies against purified human MCP. Each of them recognized different sets of MCP subunits on Western blotting. Immunohistochemically, anti-MCP antibodies recognized all ubiquitin-positive cortical LBs in situ as well as those isolated from frozen DLBD cortices, suggesting that MCP is present in LBs as a whole molecule exhibiting protease activity. In electron microscopy, MCP immunoreactivity (MCP-IR) was exclusively localized on a characteristic oval structure with an approximate diameter of 100 nm. This structure was distributed throughout the LBs and was devoid of ubiquitin immunoreactivity. Treatment of isolated LBs with 2% SDS, but not with 0.5% Triton X-100, removed this structure from LBs in which fibrous materials predominated. Ubiquitin immunoreactivity was also decreased in isolated LBs treated with 2% SDS, suggesting that the fibrous structures in LBs were not ubiquitinated in situ. Thus, it is suggested that LBs are subjected to a proteolytic process in which MCP plays a role via processing of specific components of LBs.
 ...
PMID:Multicatalytic proteinase is associated with characteristic oval structures in cortical Lewy bodies: an immunocytochemical study with light and electron microscopy. 802 94

Ubiquitin (Ub) was determined by a competitive enzyme-linked immunosorbent assay (ELISA) in serum (S) and cerebrospinal fluid (CSF) samples from 29 patients with 'probable Alzheimer's disease' (AD), 14 patients with vascular dementia (VAD), and 13 healthy individuals. The mean concentration of Ub in CSF (110 +/- 20 ng/mL) was about 20% of that in serum (940 +/- 120 ng/mL) in healthy controls. There was no significant correlation between S-Ub and CSF-Ub, or between the CSF/S.Ub ratio and the CSF/S albumin ratio. These findings suggest that a major portion of CSF-Ub is intrathecally produced. CSF-Ub was increased while S-Ub was decreased in both AD and VAD patients as compared with controls. As a consequence, the CSF/S Ub ratio showed good discrimination between patients and controls: 22/29 (76%) of the AD patients and 9/14 (64%) of the VAD patients had a CSF/S Ub ratio that was higher than the highest control value. No significant differences in any of the parameters were found between AD and VAD. Ub is involved in an ATP-dependent proteolytic pathway and also acts as a heatshock protein. The increase in CSF-Ub in AD and VAD may therefore be interpreted as a cytoprotective response to abnormal or damaged proteins, and CSF-Ub may have a potential as a non-disease-specific marker for cerebral degeneration.
 ...
PMID:Ubiquitin in cerebrospinal fluid in Alzheimer's disease and vascular dementia. 805 91

Ubiquitin modification of a variety of protein targets within the cell plays important roles in many cellular processes. Among these are regulation of gene expression, regulation of cell cycle and division, involvement in the cellular stress response, modification of cell surface receptors, DNA repair, import of proteins into mitochondria, uptake of precursors into neurons, and biogenesis of mitochondria, ribosomes, and peroxisomes. The best studied modification occurs in the ubiquitin-mediated proteolytic pathway. Degradation of a protein via the ubiquitin system involves two discrete steps. Initially, multiple ubiquitin molecules are covalently linked in an ATP-dependent mode to the protein substrate. The targeted protein is then degraded by a specific and energy-dependent high molecular mass protease into free amino acids, and free and reutilizable ubiquitin is released. In addition, stable mono-ubiquitin adducts are also found in the cell, for example, those involving nucleosomal histones. Despite the considerable progress that has been made in elucidating the mode of action and roles of the ubiquitin system, many problems remain unsolved. For example, little is known on the signals that target proteins for degradation. Although mechanistic aspects of recognition via the N-terminal residue have been studied thoroughly, it is clear that the vast majority of cellular proteins are targeted by other signals. The identity of the native cellular substrates of the system is another important, yet unresolved, problem: only few proteins have been recognized so far as substrates of the system in vivo. The scope of this review is to discuss the mechanisms involved in ubiquitin activation, selection of substrates for conjugation, and degradation of ubiquitin-conjugated proteins in the cell-free system. In addition, we shall summarize what is currently known of the physiological roles of ubiquitin-mediated proteolysis in vivo.
 ...
PMID:The ubiquitin-mediated proteolytic pathway: mechanisms of recognition of the proteolytic substrate and involvement in the degradation of native cellular proteins. 811 89

Ubiquitin-mediated proteolysis proceeds via the formation and degradation of ubiquitin-protein conjugates. Ubiquitin (Ub)-activating enzyme (E1) catalyzes the first, MgATP-dependent step in the conjugative reaction sequence. With wild type ubiquitin, the product of the E1 reaction is a ternary complex (E1-Ub-AMP-Ub) containing one thiol-linked ubiquitin (via the Ub COOH terminus, Gly-76) and one tightly bound ubiquitin adenylate. The thiol-linked ubiquitin is subsequently transferred to the thiol of a ubiquitin-conjugating enzyme (E2 protein); the latter adduct is the proximal donor of ubiquitin to the target protein. A mutant ubiquitin, bearing a Gly to Ala substitution at the COOH terminus (G76A-ubiquitin), was characterized as a substrate for E1. G76A-ubiquitin 1) supported PPi-ATP exchange poorly (500-fold decrease in kcat/K(m); 2) did not produce detectable AMP-Ub with native E1; 3) produced stoichiometric AMP-Ub with thiol-blocked E1; 4) gave a stoichiometric burst of ATP consumption (1 mol/mol E1) with either native or thiol-blocked E1; 5) supported E1-ubiquitin thiol ester formation with native E1; 6) supported several downstream reactions of the proteolytic pathway at approximately 20% of the rate of wild type ubiquitin. These results indicate that G76A-ubiquitin gives a binary E1 thiol ester complex with native E1, due to the failure of the E1-ubiquitin thiol ester to undergo another round of adenylate synthesis; thus AMP-Ub is detected only if adenylate to thiol transfer is prevented by alkylating E1. The inability of G76A-ubiquitin to support ternary complex formation has implications for E1 active site structure. In other experiments, occupancy of the nucleotide/adenylate site of E1, by either MgATP or AMP-Ub, was found to stimulate ubiquitin transthiolation between E1 and E2 proteins. The intermediacy of ubiquitin adenylate thus provides a previously unrecognized catalytic advantage in the E1 mechanism.
 ...
PMID:Substrate properties of site-specific mutant ubiquitin protein (G76A) reveal unexpected mechanistic features of ubiquitin-activating enzyme (E1). 812 20

Metabolic acidosis often leads to loss of body protein due mainly to accelerated protein breakdown in muscle. To identify which proteolytic pathway is activated, we measured protein degradation in incubated epitrochlearis muscles from acidotic (NH4Cl-treated) and pair-fed rats under conditions that block different proteolytic systems. Inhibiting lysosomal and calcium-activated proteases did not reduce the acidosis-induced increase in muscle proteolysis. However, when ATP production was also blocked, proteolysis fell to the same low level in muscles of acidotic and control rats. Acidosis, therefore, stimulates selectively an ATP-dependent, nonlysosomal, proteolytic process. We also examined whether the activated pathway involves ubiquitin and proteasomes (multicatalytic proteinases). Acidosis was associated with a 2.5- to 4-fold increase in ubiquitin mRNA in muscle. There was no increase in muscle heat shock protein 70 mRNA or in kidney ubiquitin mRNA, suggesting specificity of the response. Ubiquitin mRNA in muscle returned to control levels within 24 h after cessation of acidosis. mRNA for subunits of the proteasome (C2 and C3) in muscle were also increased 4-fold and 2.5-fold, respectively, with acidosis; mRNA for cathepsin B did not change. These results are consistent with, but do not prove that acidosis stimulates muscle proteolysis by activating the ATP-ubiquitin-proteasome-dependent, proteolytic pathway.
 ...
PMID:Metabolic acidosis stimulates muscle protein degradation by activating the adenosine triphosphate-dependent pathway involving ubiquitin and proteasomes. 818 44

We have isolated a mutant, mts2, in the fission yeast Schizosaccharomyces pombe which is defective in chromosome segregation. The predicted amino-acid sequence of the cloned mts2+ gene product is 75% identical to the S4 subunit of the human 26S ATP/ubiquitin-dependent protease. The human S4 subunit complementary DNA expressed from an S. pombe expression plasmid can rescue an S. pombe mts2 gene disruption. Both observations demonstrate that the mts2+ gene is the S. pombe homologue of the human S4 subunit. In addition, we provide genetic evidence for a physical interaction between the S4 and the related S7 subunit in the 26S multiprotein protease. We show that polyubiquitin-conjugated proteins accumulate in the mts2 mutant at the restrictive temperature, demonstrating that the mutant has an in vivo defect in the ubiquitin-dependent proteolysis pathway. Finally, the phenotype for the mts2 mutant indicates that protein degradation by the 26S protease is essential not for entry into but for the completion of mitosis.
 ...
PMID:Defective mitosis due to a mutation in the gene for a fission yeast 26S protease subunit. 824 31

Ubiquitin modification of a variety of protein targets within the cell plays important roles in many cellular processes. Among these are regulation of gene expression, regulation of cell cycle and division, involvement in the cellular stress response, modification of cell surface receptors, DNA repair, and biogenesis of mitochondria and ribosomes. The best studied modification occurs in the ubiquitin-dependent proteolytic pathway. Degradation of a protein by the ubiquitin system involves two discrete steps. Initially, multiple ubiquitin molecules are covalently linked in an ATP-dependent mode to the protein substrate. The protein moiety of the conjugate is then degraded by a specific protease into free amino acids with the release of free and reutilizable ubiquitin. This process also requires energy. In addition, stable mono-ubiquitin adducts are also found intracellularly, for example, those involving nucleosomal histones. Despite the considerable progress that has been made in elucidating the mode of action and roles of the ubiquitin system, many problems remain unsolved. For example, very little is known about the cellular substrates of the system and the signals that target them for conjugation and degradation. The scope of this review is to summarize briefly what is currently known on the role of the ubiquitin system in protein turnover, and to discuss in detail the mechanisms involved in selection of substrates for conjugation and in degradation of ubiquitin-conjugated proteins.
 ...
PMID:The ubiquitin-mediated proteolytic pathway. 826 85

Lens cells must remove obsolete or damaged proteins produced during development, maturation and aging to maintain lens transparency. In reticulocytes removal of abnormal or obsolete proteins is thought to involve a ubiquitin-dependent proteolytic pathway. Two hallmarks of ubiquitin (Ub) dependent proteolysis have previously been demonstrated in lens cell or tissue supernatants: (1) the presence of ubiquitin conjugates, and (2) ATP-dependent proteolysis. Nevertheless, conclusive proof was lacking of a requirement for ubiquitination of substrate proteins for proteolysis. Here we show that in bovine lens epithelial cell (BLEC) supernatant, ATP-dependent proteolysis is also ubiquitin-dependent. Ubiquitin-activating enzyme (E1), the first enzyme in the cascade of ubiquitin ligation, was purified over 3000-fold from a rabbit reticulocyte lysate using Ubiquitin-Sepharose, and showed ATP-PPi exchange activity. Antiserum to E1 was prepared in goats and affinity-purified on Protein G-Sepharose. Western blot analysis revealed that both the goat antiserum and purified antibody (anti-E1(IgG)) recognize specifically E1. Anti-E1(IgG) inhibits 86% of the ATP-dependent degradation of labeled histone H2A in reticulocyte lysate and 75% of the ATP-dependent degradation in BLEC. Upon reconstitution with purified E1, 100% and 80% of proteolysis was restored in reticulocytes and BLEC supernatant, respectively. This confirms that there is a ubiquitin-dependent proteolytic system in lens.
 ...
PMID:Bovine lens epithelial cells have a ubiquitin-dependent proteolysis system. 838 Mar 40

Xenopus egg extract is capable of supporting mitosis in vitro, which makes it ideal for biochemical analysis of the cell cycle. Since several studies have implicated the ubiquitin system in cell cycle progression, we have measured ubiquitin conjugation rates, proteolysis of ubiquitin-lysozyme conjugates, and rates of isopeptidase activity in cycling Xenopus egg extracts. Although ubiquitin conjugation in cytostatic factor arrested extract was half that in activated extract, there were no changes in rates of ubiquitin conjugation during the cell cycle. Ubiquitin conjugates are degraded by a 26 S ATP-stimulated protease. The ability of the 26 S protease to degrade ubiquitin-lysozyme conjugates and a fluorigenic peptide also remained constant across the cell cycle. In contrast to previously characterized systems, isopeptidase activity in Xenopus egg extract is energy-dependent. Glycerol gradient fractionation of Xenopus egg extract separated two ATP-dependent isopeptidases. On co-sedimented with the 26 S protease; the other sedimented slower and was not associated with any additional proteolytic activity. As found for rates of Ub conjugation and conjugate proteolysis, there was little or no variation in isopeptidase activity during the cell cycle.
 ...
PMID:Ubiquitin metabolism in cycling Xenopus egg extracts. 840 56


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>