Avicins are a recently discovered family of plant-derived terpenoid molecules that possess proapoptotic, antiinflammatory, and cytoprotective properties in mammalian cells. Previous work ...demonstrating that avicins can exert their effects by suppressing or activating the redox-sensitive transcription factors NF-κB and nuclear factor-erythroid 2 p45-related factor (Nrf2), respectively, has raised the idea that they may react with critical cysteine residues. To understand the molecular mechanism through which avicins regulate protein function, we examined their effects on the paradigmatic redox-responsive transcriptional activator, OxyR of Escherichia coli, which protects bacterial cells against oxidative and nitrosative stresses. In vitro transcription assays demonstrated that avicins activate OxyR and its target genes katG and oxyS in a DTT-reversible manner. In addition, katG-dependent hydroperoxidase I activity was enhanced in avicin-treated bacteria. Mass spectrometric analysis of activated OxyR revealed thioesterification of the critical regulatory cysteine, Cys-199, to an avicin fragment comprising the outer monoterpene side chain. Our results indicate that avicinylation can induce adaptive responses that protect cells against oxidative or nitrosative stress. More generally, transesterification may represent a previously undescribed thioldirected posttranslational modification, which extends the code for redox regulation of protein function.
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Nitric oxide (NO) and related molecules play important roles in vascular biology. NO modifies proteins through nitrosylation of free cysteine residues, and such modifications are important in ...mediating NO's biologic activity. Tissue transglutaminase (tTG) is a sulfhydryl rich protein that is expressed by endothelial cells and secreted into the extracellular matrix (ECM) where it is bound to fibronectin. Tissue TG exhibits a Ca2+-dependent transglutaminase activity (TGase) that cross-links proteins involved in wound healing, tissue remodeling, and ECM stabilization. Since tTG is in proximity to sites of NO production, has 18 free cysteine residues, and utilizes a cysteine for catalysis, we investigated the factors that regulated NO binding and tTG activity. We report that TGase activity is regulated by NO through a unique Ca2+-dependent mechanism. Tissue TG can be poly-S-nitrosylated by the NO carrier, S-nitrosocysteine (CysNO). In the absence of Ca2+, up to eight cysteines were nitrosylated without modifying TGase activity. In the presence of Ca2+, up to 15 cysteines were found to be nitrosylated and this modification resulted in an inhibition of TGase activity. The addition of Ca2+ to nitrosylated tTG was able to trigger the release of NO groups (i.e. denitrosylation). tTG nitrosylated in the absence of Ca2+ was 6-fold more susceptible to inhibition by Mg-GTP. When endothelial cells in culture were incubated with tTG and stimulated to produce NO, the exogenous tTG was S-nitrosylated. Furthermore, S-nitrosylated tTG inhibited platelet aggregation induced by ADP. In conclusion, we provide evidence that Ca2+ regulates the S-nitrosylation and denitrosylation of tTG and thereby TGase activity. These data suggest a novel allosteric role for Ca2+ in regulating the inhibition of tTG by NO and a novel function for tTG in dispensing NO bioactivity.
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5.
Fusion of radioactive 132Sn with 64Ni Liang, J Felix; Shapira, Dan; Beene, James R ...
Physical review. C, Nuclear physics,
01/2007, Volume:
75, Issue:
5
Journal Article
Evaporation residue and fission cross sections of radioactive 132Sn on 64Ni were measured near the Coulomb barrier. A large subbarrier fusion enhancement was observed. Coupled-channel calculations, ...including inelastic excitation of the projectile and target, and neutron transfer are in good agreement with the measured fusion excitation function. When the change in nuclear size and shift in barrier height are accounted for, there is no extra fusion enhancement in 132Sn+64Ni with respect to stable Sn+64Ni. A systematic comparison of evaporation residue cross sections for the fusion of even 112-124Sn and 132Sn with 64Ni is presented.
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