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21.
Baek KT Vegge CS Skórko-Glonek J Brøndsted L 《Applied and environmental microbiology》2011,77(1):57-66
The microaerophilic bacterium Campylobacter jejuni is the most common cause of bacterial food-borne infections in the developed world. Tolerance to environmental stress relies on proteases and chaperones in the cell envelope, such as HtrA and SurA. HtrA displays both chaperone and protease activities, but little is known about how each of these activities contributes to stress tolerance in bacteria. In vitro experiments showed temperature-dependent protease and chaperone activities of C. jejuni HtrA. A C. jejuni mutant lacking only the protease activity of HtrA was used to show that the HtrA chaperone activity is sufficient for growth at high temperature or under oxidative stress, whereas the HtrA protease activity is essential only under conditions close to the growth limit for C. jejuni. However, the protease activity was required to prevent induction of the cytoplasmic heat shock response even under optimal growth conditions. Interestingly, the requirement of HtrA at high temperatures was found to depend on the oxygen level, and our data suggest that HtrA may protect oxidatively damaged proteins. Finally, protease activity stimulates HtrA production and oligomer formation, suggesting that a regulatory role depends on the protease activity of HtrA. Studying a microaerophilic organism encoding only two known periplasmic chaperones (HtrA and SurA) revealed an efficient HtrA chaperone activity and proposed multiple roles of the protease activity, increasing our understanding of HtrA in bacterial physiology. 相似文献
22.
Rutkowska J Badyaev AV 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2008,363(1497):1675-1686
Differences in relative fitness of male and female offspring across ecological and social environments should favour the evolution of sex-determining mechanisms that enable adjustment of brood sex ratio to the context of breeding. Despite the expectation that genetic sex determination should not produce consistent bias in primary sex ratios, extensive and adaptive modifications of offspring sex ratio in relation to social and physiological conditions during reproduction are often documented. Such discordance emphasizes the need for empirical investigation of the proximate mechanisms for modifying primary sex ratios, and suggests epigenetic effects on sex-determining mechanisms as the most likely candidates. Birds, in particular, are thought to have an unusually direct opportunity to modify offspring sex ratio because avian females are heterogametic and because the sex-determining division in avian meiosis occurs prior to ovulation and fertilization. However, despite evidence of strong epigenetic effects on sex determination in pre-ovulatory avian oocytes, the mechanisms behind such effects remain elusive. Our review of molecular and cytological mechanisms of avian meiosis uncovers a multitude of potential targets for selection on biased segregation of sex chromosomes, which may reflect the diversity of mechanisms and levels on which such selection operates in birds. Our findings indicate that pronounced differences between sex chromosomes in size, shape, size of protein bodies, alignment at the meiotic plate, microtubule attachment and epigenetic markings should commonly produce biased segregation of sex chromosomes as the default state, with secondary evolution of compensatory mechanisms necessary to maintain unbiased meiosis. We suggest that it is the epigenetic effects that modify such compensatory mechanisms that enable context-dependent and precise adjustment of primary sex ratio in birds. Furthermore, we highlight the features of avian meiosis that can be influenced by maternal hormones in response to environmental stimuli and may account for the precise and adaptive patterns of offspring sex ratio adjustment observed in some species. 相似文献
23.
Sarker P Shepherd J Swindells K Douglas I MacNeil S Swanson L Rimmer S 《Biomacromolecules》2011,12(1):1-5
Polymyxin peptide conjugated to the end groups of highly branched poly(N-isopropyl acrylamide) was shown to bind to a Gram negative bacterium, Pseudomonas aeruginosa . The nonbound polymer had a lower critical solution temperature (LCST) above 60 °C. However, binding caused aggregation, which was disrupted on cooling of the bacteria and polymer mixture. The data indicate that polymer binding of bacteria occurred by interaction of the end groups with lipopolysaccharide and that the binding decreased the LCST to below 37 °C. Cooling then progressed the polymer/bacteria aggregate through a bound LCST into an open polymer coil conformation that was not adhesive to P. aeruginosa . 相似文献
24.
Nichola A. Strandberg Mary Edwards Joanna C. Ellison Manuel J. Steinbauer Anna Walentowitz Patricia L. Fall David Sear Peter Langdon Shane Cronin Alvaro Castilla-Beltrán Ian W. Croudace Matiu Prebble William D. Gosling Sandra Nogué 《Biotropica》2023,55(4):816-827
Here, we investigate Mid- to Late-Holocene vegetation changes in low-lying coastal areas in Tonga and how changing sea levels and recurrent volcanic eruptions have influenced vegetation dynamics on four islands of the Tongan archipelago (South Pacific). To investigate past vegetation and environmental change at Ngofe Marsh (‘Uta Vava’u), we examined palynomorphs (pollen and spores), charcoal (fire), and sediment characteristics (volcanic activity) from a 6.7-m-long sediment core. Radiocarbon dating indicated the sediments were deposited over the last 7700 years. We integrated the Ngofe Marsh data with similar previously published data from Avai’o’vuna Swamp on Pangaimotu Island, Lotofoa Swamp on Foa Island, and Finemui Swamp on Ha’afeva Island. Plant taxa were categorized as littoral, mangrove, rainforest, successional/ disturbance, and wetland groups, and linear models were used to examine relationships between vegetation, relative sea level change, and volcanic eruptions (tephra). We found that relative sea level change has impacted vegetation on three of the four islands investigated. Volcanic eruptions were not identified as a driver of vegetation change. Rainforest decline does not appear to be driven by sea level changes or volcanic eruptions. From all sites analyzed, vegetation at Finemui Swamp was most sensitive to changes in relative sea level. While vegetation on low-lying Pacific islands is sensitive to changing sea levels, island characteristics, such as area and elevation, are also likely to be important factors that mediate specific island responses to drivers of change. 相似文献
25.
Wisniewska-Jarosinska M Poplawski T Chojnacki CJ Pawlowska E Krupa R Szczepanska J Blasiak J 《Molecular biology reports》2011,38(7):4603-4611
Dental composite materials contain polymers of methacrylates, which, due to mechanical abrasion and enzymatic action of saliva,
may release their monomers into oral cavity and the pulp. Moreover, polymerization is always incomplete and leaves usually
considerable fraction of free monomers. Mechanisms of the genotoxicity of methacrylate monomers have been rarely explored.
As the polymerization of a monomer is catalyzed by a co-monomer, their combined action should be considered. In the present
work, we investigated cytotoxic and genotoxic effects of urethane dimethacrylate (UDMA), often used as a monomer, at 1 mM,
and triethylene glycol dimethacrylate (TEGDMA), a typical co-monomer, at 5 mM singly and in combination. Experiments were
conducted on Chinese hamster ovary cells. Cell viability, apoptosis and cell cycle were assessed by flow cytometry, whereas
DNA damage was evaluated by plasmid conformation test and comet assay. Both compounds decreased the viability of the cells,
but did not induce strand breaks in an isolated plasmid DNA. However, both substances, either singly or in combination, damaged
DNA in CHO cells as evaluated by comet assay. Both compounds induced apoptosis, but a combined action of them led to a decrease
in the number of apoptotic cells. The combined action of UDMA and TEGDMA in the disturbance of cell cycle was lesser compared
to the action of each compound individually. Individually, though UDMA and TEGDMA may induce cytotoxic and genotoxic, however,
a combination of both does not produce a significant increase in these effects. 相似文献
26.
Toll-like receptor (TLR) 2 and TLR5, but not TLR4, are required for Helicobacter pylori-induced NF-kappa B activation and chemokine expression by epithelial cells 总被引:11,自引:0,他引:11
Smith MF Mitchell A Li G Ding S Fitzmaurice AM Ryan K Crowe S Goldberg JB 《The Journal of biological chemistry》2003,278(35):32552-32560
27.
Our study focused on the relationship between amyloid β 1–42 (Aβ), sphingosine kinases (SphKs) and mitochondrial sirtuins in regulating cell fate. SphK1 is a key enzyme involved in maintaining sphingolipid rheostat in the brain. Deregulation of the sphingolipid metabolism may play a crucial role in the pathogenesis of Alzheimer’s disease (AD). Mitochondrial function and mitochondrial deacetylases, i.e. sirtuins (Sirt3,-4,-5), are also important for cell viability. In this study, we evaluated the interaction between Aβ1–42, SphKs and Sirts in cell survival/death, and we examined several compounds to indicate possible target(s) for a strategy protecting against cytotoxicity of Aβ1–42. PC12 cells were subjected to Aβ1–42 oligomers and SphK inhibitor SKI II for 24–96 h. Our data indicated that Aβ1–42 enhanced SphK1 expression and activity after 24 h, but down-regulated them after 96 h and had no effect on Sphk2. Aβ1–42 and SKI II induced free radical formation, disturbed the balance between pro- and anti-apoptotic proteins and evoked cell death. Simultaneously, up-regulation of anti-oxidative enzymes catalase and superoxide dismutase 2 was observed. Moreover, the total protein level of glycogen synthase kinase-3β was decreased. Aβ1–42 significantly increased the level of mitochondrial proteins: apoptosis-inducing factor AIF and Sirt3, -4, -5. By using several pharmacologically active compounds we showed that p53 protein plays a significant role at very early stages of Aβ1–42 toxicity. However, during prolonged exposure to Aβ1–42, the activation of caspases, MEK/ERK, and alterations in mitochondrial permeability transition pores were additional factors leading to cell death. Moreover, SphK product, sphingosine-1-phosphate (S1P), and Sirt activators and antioxidants, resveratrol and quercetin, significantly enhanced viability of cells subjected to Aβ1–42. Our data indicated that p53 protein and inhibition of SphKs may be early key events responsible for cell death evoked by Aβ1–42. We suggest that activation of S1P-dependent signalling and Sirts may offer a promising cytoprotective strategy. 相似文献
28.
29.
DiDonato M Krishna SS Schwarzenbacher R McMullan D Jaroszewski L Miller MD Abdubek P Agarwalla S Ambing E Axelrod H Biorac T Chiu HJ Deacon AM Elsliger MA Feuerhelm J Godzik A Grittini C Grzechnik SK Hale J Hampton E Haugen J Hornsby M Klock HE Knuth MW Koesema E Kreusch A Kuhn P Lesley SA Moy K Nigoghossian E Okach L Paulsen J Quijano K Reyes R Rife C Spraggon G Stevens RC van den Bedem H Velasquez J White A Wolf G Xu Q Hodgson KO Wooley J Wilson IA 《Proteins》2006,63(1):256-260
30.
Although Lrp5 is known to be an important contributor to the mechanisms regulating bone mass, its precise role remains unclear. The aim of this study was to establish whether mutations in Lrp5 are associated with differences in the growth and/or apoptosis of osteoblast-like cells and their proliferative response to mechanical strain in vitro. Primary osteoblast-like cells were derived from cortical bone of adult mice lacking functional Lrp5 (Lrp5(-/-)), those heterozygous for the human G171V High Bone Mass (HBM) mutation (LRP5(G171V)) and their WT littermates (WT(Lrp5), WT(HBM)). Osteoblast proliferation over time was significantly higher in cultures of cells from LRP5(G171V) mice compared to their WT(HBM) littermates, and lower in Lrp5(-/-) cells. Cells from female LRP5(G171V) mice grew more rapidly than those from males, whereas cells from female Lrp5(-/-) mice grew more slowly than those from males. Apoptosis induced by serum withdrawal was significantly higher in cultures from Lrp5(-/-) mice than in those from WT(HBM) or LRP5(G171V) mice. Exposure to a single short period of dynamic mechanical strain was associated with a significant increase in cell number but this response was unaffected by genotype which also did not change the 'threshold' at which cells responded to strain. In conclusion, the data presented here suggest that Lrp5 loss and gain of function mutations result in cell-autonomous alterations in osteoblast proliferation and apoptosis but do not alter the proliferative response of osteoblasts to mechanical strain in vitro. 相似文献