FEBS Letters
0014-5793
Cơ quản chủ quản: WILEY , Wiley-Blackwell
Lĩnh vực:
Molecular BiologyBiochemistryBiophysicsGeneticsCell BiologyStructural Biology
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Effect of a negative regulatory element (NRE) on the human CYP1A1 gene expression in breast carcinoma MCF-7 and hepatoma HepG2 cells
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Cysteine‐153 is required for redox regulation of pea chloroplast fructose‐1,6‐bisphosphatase Chloroplastic fructose‐1,6‐bisphosphatases are redox regulatory enzymes which are activated by the ferredoxin thioredoxin system via the reduction/isomerization of a critical disulfide bridge. All chloroplastic sequences contain seven cysteine residues, four of which are located in, or close to, an amino acid insertion region of approximately 17 amino acids. In order to gain more information on the nature of the regulatory site, five cysteine residues (Cys49 , Cys153 , Cys173 , Cys178 and Cys190 ) have been modified individually into serine residues by site‐directed mutagenesis. While mutations C173S and C178S strongly affected the redox regulatory properties of the enzyme, the most striking effect was observed with the C153S mutant which became permanently active and redox independent. On the other hand, the C190S mutant retained most of the properties of the wild‐type enzyme (except that it could now also be partially activated by the NADPH/NTR/thioredoxin h system). Finally, the C49S mutant is essentially identical to the wild‐type enzyme. These results are discussed in the light of recent crystallographic data obtained on spinach FBPase [Villeret et al. (1995) Biochemistry 34, 4299–4306].
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Characterization of thioredoxin <i>y</i>, a new type of thioredoxin identified in the genome of <i>Chlamydomonas reinhardtii</i> The sequencing of the Arabidopsis genome revealed a multiplicity of thioredoxins (TRX), ubiquitous protein disulfide oxido‐reductases. We have analyzed the TRX family in the genome of the unicellular green alga Chlamydomonas reinhardtii and identified eight different thioredoxins for which we have cloned and sequenced the corresponding cDNAs. One of these TRXs represents a new type that we named TRX y . This most probably chloroplastic TRX is highly conserved in photosynthetic organisms. The biochemical characterization of the recombinant protein shows that it exhibits a thermal stability profile and specificity toward target enzymes completely different from those of TRXs characterized so far.
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Both oxidative and nitrosative stress are associated with muscle wasting in tumour‐bearing rats Reactive oxygen and nitrogen species (ROS and RNS) have been proposed as mechanisms of cancer‐induced cachexia. In this study, we assessed using Western blot analysis the levels of total protein carbonylation (2,4‐dinitrophenylhydrazine assay), both malondialdehyde‐ (MDA‐) and 2‐hydroxy‐4‐nonenal‐ (HNE‐) protein adducts, Mn‐superoxide dismutase (Mn‐SOD), catalase, heme oxygenase‐1 (HO‐1) and 3‐nitrotyrosine formation in gastrocnemius muscles of rats bearing the Yoshida AH‐130 hepatoma. In the muscles of the tumour‐bearing animals, protein carbonylation as measured by total levels of carbonyl group formation and both HNE and MDA‐protein adducts, and protein tyrosine nitration were significantly greater than in control muscles. Protein levels of the antioxidant enzymes Mn‐SOD, catalase, and HO‐1 were not significantly modified in the rat cachectic muscles compared to controls. The inefficiency of the antioxidant enzymes in neutralizing excessive ROS production may account for elevated markers of protein oxidation and be responsible for the development of both oxidative and nitrosative stress in cancer‐induced cachexia.
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Purification of <i>N</i>‐acetyl β‐D‐hexosaminidase from bull epididymis by affinity chromatography
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Pertussis toxin‐dependent and ‐independent hormonal effects on cultured renal epithelioid cells The present study has been performed to test for the involvement of pertussis toxin‐sensitive GTP‐binding proteins (G‐proteins) in the cellular transduction of hormone‐induced activation of potassium channels. In Madin Darby canine kidney (MDCK) cells, a permanent cell line from dog kidney, epinephrine, acetylcholine, bradykinin, serotonin and ATP hyperpolarize the cell membrane by activation of potassium channels. In cells pretreated with pertussis toxin the hyperpolarizations elicited by either acetylcholine or serotonin are completely abolished; that following epinephrine is blunted and only transient. The hyperpolarizing effects of ATP or bradykinin are not affected by pertussis toxin. Thus, in MDCK cells both pertussis toxin‐dependent and ‐independent mechanisms operate in parallel to enhance the potassium conductance of the cell membrane.
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CO<sub>2</sub> response for expression of ribulose‐1,5‐bisphosphate carboxylase/oxygenase genes is inhibited by AT‐rich decoy in the cyanobacterium The CO2 ‐regulatory function of the AT‐rich element in the promoter for ribulose‐1,5‐bisphosphate carboxylase/oxygenase (rbc ) genes in the cyanobacterium Synechococcus sp. PCC7002 was analyzed using the transcription factor decoy approach. Double‐stranded phosphorothioate AT‐rich oligonucleotides with high affinity for a sequence‐specific DNA‐binding protein were successfully introduced into cyanobacterial cells in culture without any transfection reagent. The AT‐rich decoy oligonucleotides interfered with CO2 regulation of rbc expression by blocking the binding of the sequence‐specific DNA‐binding protein, indicating that the AT‐rich element plays a critical role in CO2 regulation for rbc genes. The decoy oligonucleotide approach to cyanobacteria provides a simple and excellent tool for investigating transcriptional regulation in vivo.
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Molecular mechanisms underlying endocytosis and sorting of ErbB receptor tyrosine kinases The major process that regulates the amplitude and kinetics of signal transduction by tyrosine kinase receptors is endocytic removal of active ligand–receptor complexes from the cell surface, and their subsequent sorting to degradation or to recycling. Using the ErbB family of receptor tyrosine kinases we exemplify the diversity of the down regulation process, and concentrate on two sorting steps whose molecular details are emerging. These are the Eps15‐mediated sorting to clathrin‐coated regions of the plasma membrane and the c‐Cbl‐mediated targeting of receptors to lysosomal degradation. Like in yeast cells, sorting involves not only protein phosphorylation but also conjugation of ubiquitin molecules. The involvement of other molecules is reviewed and recent observations that challenge the negative regulatory role of endocytosis are described. Finally, we discuss the relevance of receptor down regulation to cancer therapy.
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