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1.
Abhishek Chatterjee Celia Caballero-Franco Dannika Bakker Stephanie Totten Armando Jardim 《The Journal of biological chemistry》2015,290(42):25579-25594
Enterohemorrhagic Escherichia coli is a causative agent of gastrointestinal and diarrheal diseases. Pathogenesis associated with enterohemorrhagic E. coli involves direct delivery of virulence factors from the bacteria into epithelial cell cytosol via a syringe-like organelle known as the type III secretion system. The type III secretion system protein EspD is a critical factor required for formation of a translocation pore on the host cell membrane. Here, we show that recombinant EspD spontaneously integrates into large unilamellar vesicle (LUV) lipid bilayers; however, pore formation required incorporation of anionic phospholipids such as phosphatidylserine and an acidic pH. Leakage assays performed with fluorescent dextrans confirmed that EspD formed a structure with an inner diameter of ∼2.5 nm. Protease mapping indicated that the two transmembrane helical hairpin of EspD penetrated the lipid layer positioning the N- and C-terminal domains on the extralumenal surface of LUVs. Finally, a combination of glutaraldehyde cross-linking and rate zonal centrifugation suggested that EspD in LUV membranes forms an ∼280–320-kDa oligomeric structure consisting of ∼6–7 subunits. 相似文献
2.
Fine root distribution of trees and understory in mature stands of maritime pine (Pinus pinaster) on dry and humid sites 总被引:2,自引:0,他引:2
Maritime pine (Pinus pinaster) is the main tree cropping species in the Landes of Gascogne forest range in south western France. Soils are nutrient poor, sandy podzosols and site fertility is determined essentially by organic matter content and depth of water table, which is known to limit root growth. We hypothesised, with an ultimate goal of constructing a nutrient uptake model applicable to this region, that the organic top horizons together with the depth of the water table should be the most important parameters related to fine root distribution and presence of associated mycorrhiza. To test this hypothesis, we compared two adult Pinus pinaster stands, contrasting in depth of water table and soil fertility and evaluated fine roots (diameter ≤2 mm) of understory species and fine roots and ectomycorrhizal morphotypes of Pinus pinaster down to 1.2 m, using a soil corer approach. Total fine root biomass of Pinus pinaster was not significantly different between both sites (3.6 and 4.5 t ha−1 for the humid, respectively, dry site), but root distribution was significantly shallower and root diameter increased more with depth at the humid site, presumably due to more adverse soil conditions as related to the presence of a hardpan, higher amount of aluminium oxides and / or anoxia. Fine roots of Pinus pinaster represented only about 30% of total fine root biomass and 15% of total fine root length, suggesting that the understory species cannot be ignored with regards to competition for mineral nutrients and water. A comparison of the ectomycorrhizal morphotypes showed that the humid site could be characterised by a very large proportion of contact exploration types, thought to be more relevant in accessing organic nutrient sources, whereas the dry site had a significantly higher proportion of both long-distance and short-distance exploration types, the latter of which was thought to be more resistant to short-term drought periods. These results partly confirm our hypothesis on root distribution as related to the presence of soil mineral nutrients (i.e. in organic matter), point out the potential role of understory plant species and ectomycorrhizal symbiosis and are a valuable step in building a site-specific nutrient uptake model. 相似文献
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4.
Marion Mehlis Ingolf P. Rick Theo C. M. Bakker 《Proceedings. Biological sciences / The Royal Society》2015,282(1817)
In polyandrous mating systems, male reproductive success depends on both mate-acquisition traits (precopulatory) and sperm competitive abilities (postcopulatory). Empirical data on the interaction between these traits are inconsistent; revealing positive, negative or no relationships. It is generally expected that the investment in pre- and postcopulatory traits is mediated by environmental conditions. To test how dietary resource availability affects sexual ornamentation, sperm quality and their interrelationship in three-spined sticklebacks (Gasterosteus aculeatus), full-sibling groups were raised under three conditions differing in food quantity and/or quality (i.e. carotenoid content): (i) high-quantity/high-quality, (ii) high-quantity/low-quality or (iii) low-quantity/low-quality. After 1 year of feeding, food-restricted males developed a more intense breeding coloration and faster sperm compared with their well-fed brothers, indicating that they allocated relatively more in pre- and postcopulatory traits. Moreover, they outcompeted their well-fed, carotenoid-supplemented brothers in sperm competition trials with equal numbers of competing sperm, suggesting that food-restricted males maximize their present reproductive success. This may result in reduced future reproductive opportunities as food-restricted males suffered from a higher mortality, had an overall reduced body size, and sperm number available for fertilization. In accordance with theory, a trade-off between the investment in pre- and postcopulatory traits was observed in food-restricted males, whereas well-fed males were able to allocate to both traits resulting in a significantly positive relationship. 相似文献
5.
Host discrimination studies were conducted with different species of Asobara, which are larval endo-parasitoids of Drosophilidae. Results indicated variable host discrimination which depended on the relatedness of the species. The closely related sibling species Asobara tabida (Nees) and A. rufescens (Foerster) were not only capable of intraspecific discrimination, but also avoided multiparasitism by discriminating between unparasitized host larvae and larvae previously parasitized by females of the other species. This ability to discriminate interspecifically does not seem functional as each species occupies its own microhabitat. As it was shown to be absent in less closely related Asobara species we concluded that interspecific discrimination by A. tabida and A. rufescens was due to their close relationship. 相似文献
6.
Efficient isolation of X chromosome-specific single-copy probes from a cosmid library of a human X/hamster hybrid-cell line: mapping of new probes close to the locus for X-linked mental retardation. 总被引:18,自引:12,他引:6
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M H Hofker A A Bergen M I Skraastad N J Carpenter H Veenema J M Connor E Bakker G J van Ommen P L Pearson 《American journal of human genetics》1987,40(4):312-328
We isolated X-chromosomal DNA probes from a cosmid library constructed from a single human X/hamster hybrid-cell line (C12D). One hundred human clones were isolated and used to construct a pool of X-chromosomal DNA. This DNA was digested into 0.15-2-kb fragments and subcloned into plasmids allowing the rapid characterization of new single-copy probes. These were regionally mapped and used for the detection of restriction-site polymorphisms. Together with a series of subcloned probes from individually isolated cosmids, we found seven polymorphic probes among 53 tested. Thirty-one of the probes were physically localized to different regions of the X chromosome. Four polymorphic probes map to Xq27-Xq28: DXS102 (cX38.1), DXS105(cX55.7), DXS107(cpX234), and DXS134(cpX67). These were genetically mapped by multipoint analysis relative to previously characterized loci, a mapping that resulted in the following order: DXYS1, DXS107, DXS51/DXS102, F9, DXS105, Fra-X, F8/DXS52, DXS15, DXS134. The mapping of DXS105 between F9 and Fra-X makes this probe useful for Fra-X analysis. For the linkage between FraX and DXS105, a maximum lod score of 5.01 at 4 cMorgans has been obtained in one large Dutch pedigree. 相似文献
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8.
Sera from three chimpanzees infected with a primary lymphadenopathy-associated virus (LAV-1) or human T-lymphotropic virus type III (HTLV-IIIB) passage, from two chimpanzees infected with blood from the primary infected chimpanzees, and from one chimpanzee infected with blood from a secondary passage animal all bound the peptides 3B and 3B/RF, sharing the sequence IQRGPGR, with equally high titers. Pepscan analysis confirmed the amino acids Q, R, G, P, and G as irreplaceable in order to retain antigenicity. 相似文献
9.
J. Visscher R. van der Woerd C. G. Bakker Alan W. Schwartz 《Origins of life and evolution of the biosphere》1989,19(1):3-6
Evidence is presented that a poly(U) template selectively favors the oligomerization of the activated, 3–5 pyrophosphate-linked dimer pdAppdAp, in comparison with the 3–3 and 5–5 linked dimers. In the absence of poly(U), the 5–5linked dimer is the most reactive, and chains are formed which are more than 60 monomer units in length.Nucleic Acid-Like Structures V. For the previous paper in this series see Visscher and Schwartz (1988). 相似文献
10.
B. L. Simons P. T. J. Willemsen D. Bakker B. Roosendaal F. K. De Graaf B. Oudega 《Molecular microbiology》1990,4(12):2041-2050
The DNA sequence of the K99 fanF gene, encoding FanF, was determined. An open reading frame of 999 bp was found. The primary structure of FanF was deduced and analysis revealed the presence of a signal sequence of 22 amino acid residues. The mature protein contains 311 amino acid residues (Mr 33,905 D). The amino acid sequence of FanF showed similarity with the K88ab major subunit FaeG. A specific mouse antiserum against FanF was prepared by constructing and purifying a hybrid Cro-LacZ-FanF protein. Minicell analysis, immunoblotting and immunoelectronmicroscopy revealed a pool of FanF in the periplasm of K99-producing cells and showed, furthermore, that FanF is a minor component of K99 fibrillae, present at the top and in or along the shaft of the K99 fibrillar structures. A fanF mutant plasmid was constructed. Cells harbouring this plasmid produced all K99-specific proteins, except FanF, but produced 0.1% of the K99 fibrillae relative to 'normal' K99-producing cells. Electron microscopic observations showed that cells defective in fanF produce only a few (apparently short) K99 fibrillae. FanF, therefore, was supposed to play a role in initiation and elongation of K99 fibrillae formation. Thin-layer chromatography experiments involving purified receptor material showed that FanF is not required for binding of K99 fibrillae to the ganglioside receptor. Fibrillae produced by an adhesion-negative strain carrying a mutation in the K99 major fibrillar subunit were shown to contain a normal amount of FanF. 相似文献