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The large microtubule-associated/Ca2+-signalling protein p600 (also known as UBR4) is required for hippocampal neuronal survival upon Ca2+ dyshomeostasis induced by glutamate treatment. During this process, p600 prevents aggregation of the Ca2+/calmodulin-dependent kinase IIα (CaMKIIα), a proxy of neuronal death, via direct binding to calmodulin in a microtubuleindependent manner. Using photoconductive stimulation coupled with live imaging of single neurons, we identified a distinct mechanism of prevention of CaMKIIα aggregation by p600. Upon direct depolarization, CaMKIIα translocates to microtubules. In the absence of p600, this translocation is interrupted in favour of a sustained self-aggregation that is prevented by the microtubule-stabilizing drug paclitaxel. Thus, during photoconductive stimulation, p600 prevents the aggregation of CaMKIIα by stabilizing microtubules. The effectiveness of this stabilization for preventing CaMKIIα aggregation during direct depolarization but not during glutamate treatment suggests a model wherein p600 has two modes of action depending on the source of cytosolic Ca2+.
The effect of immobilization in bed on metabolism and function of human blood platelet was studied. Blood platelets taken from patients with bone fractures after long term bed rest (14 days and 28 days) demonstrated significantly reduced concentration of total adenine nucleotides (after 28 days reduction about 30%). This decrease of total platelet adenine nucleotides af er immobilization in bed is probably caused by s imulation of platelet secretory process. Thrombin which released from confrol platele s 58.2%±1.5% of total adenine nucleotides liberated decreased amounfs (only 23.1 %±3.3% of total) of nucleotides from patient platelets isolated after 28 days of immobilization in bed. Loss of nucleotides from platelets was accompanied by sligh ly increased extent of platelet aggregation. It is concluded that during bed rest the reactivity of blood platelets (aggregation and release reaction) is stimulated.
Aggregation of Aβ peptides is a seminal event in Alzheimer’s disease. Detailed understanding of Aβ assembly would facilitate the targeting and design of fibrillogenesis inhibitors. Here comparative conformational and aggregation studies using CD spectroscopy and thioflavine T fluorescence assay are presented. As a model peptide, the 11–28 fragment of Aβ was used. This model peptide is known to contain the core region responsible for Aβ aggregation. The structural and aggregational behaviour of the peptide was compared with the properties of its variants corresponding to natural, clinically relevant mutants at positions 21-23 (A21G, E22K, E22G, E22Q and D23N). In HFIP (hexafluoro-2-propanol), a strong α-helix inducer, the CD spectra revealed an unexpectedly high amount of β-sheet conformation. The aggregation process of Aβ(11–28) variants provoked by water addition to HFIP was found to be consistent with a model of an α-helix-containing intermediate. The aggregation propensity of all Aβ(11–28) variants was also compared and discussed.
Direct interactions between collagen, the most thrombogenic component of the extracellular matrix, and platelet surface membrane receptors mediate platelet adhe­sion and induce platelet activation and aggregation. In this process two glyco- proteins are crucial: integrin a2β1, an adhesive receptor, and GPVI, which is espe­cially responsible for signal transduction. Specific antagonists of the collagen recep­tors are useful tools for investigating the complexity of platelet-collagen interactions. In this work we assessed the usefulness of DGEA peptide (Asp-Gly-Glu-Ala), the shortest collagen type I-derived motif recognised by the collagen-binding integrin a2β1, as a potential antagonist of collagen receptors. We examined platelet function using several methods including platelet adhesion under static conditions, platelet function analyser PFA-100™, whole blood electric impedance aggregometry (WBEA) and flow cytometry. We found that DGEA significantly inhibited adhesion, aggrega­tion and release reaction of collagen activated blood platelets. The inhibitory effect of DGEA on static platelet adhesion reached sub-maximal values at millimolar inhibi­tor concentrations, whereas the specific blocker of a2β1 — monoclonal antibodies Gi9, when used at saturating concentrations, had only a moderate inhibitory effect on platelet adhesion. Considering that 25-30% of total collagen binding to is specific, we conclude that DGEA is a strong antagonist interfering with a variety of collagen-platelet inter­actions, and it can be recognised not only by the primary platelet adhesion receptor but also by other collagen receptors.
The evergreen, semi-parasitic pine mistletoe, Viscum album ssp. austriacum (Wiesb.) Volmann, is one of the four subspecies of European mistletoe, Viscum album L. It is frequently encountered on Scots pine communities in Poland. Distribution of pine mistletoe in representative P. sylvestris stand from the central Poland was investigated. The host density and host size to the frequency of Viscum was verified. Within the studied area 46% out of 313 individuals of P. sylvestris trees were infected by mistletoe, among them 78% in low mistletoe infection, 17% in medium and 3% in high infection. Of 1171 infections recorded on pines, 97% were on branches, 4% on the host trunk. The mistletoe individuals had an aggregated pattern of spatial distribution which was mainly explained by the host size. Infected trees are larger than uninfected ones, on average, and within the infected tree population, trees with mistletoe had higher number of dead branches than trees with none infection. Parasitized trees were more prevalent in low-density stands than in high-density stands. Mistletoes occurred mainly on the outer brunches within trees crowns.
Urinary tract infections are the most common health problem affecting millions of people each year. Uropathogenic Escherichia coli (UPEC) strains are the major factor causing lower and upper urinary tract infections. UPEC produce several virulence factors among which are surface exposed adhesive organelles (pili/fimbriae) responsible for colonization, invasion and amplification within uroepithelial cells. The virulence of the uropathogenic E. coli Dr⁺ IH11128 is associated with Dr fimbriae belonging to the Dr family of adhesins (associated with diarrhea and urinary tract infections) and a DraD protein capping the linear fiber at the bacterial cell surface. In this study we revealed that biofilm development can be another urovirulence determinant allowing pathogenic E. coli Dr⁺ to survive within the urinary tract. E. coli strains were grown in rich or minimal media, allowed to adhere to abiotic surfaces and analyzed microscopically by staining of cells with cristal violet. We found that both Dr fimbriae and DraD, exposed at the cell surface in two forms, fimbria-assoeiated or fimbria non-associated, (DraE⁺/DraD⁺, DraE⁺/DraD⁻ or DraE⁻/DraD⁺ E. coli strains) are required for biofilm formation. Additionally, we demonstrated the biofilm formation capacity of E. coli strains deficient in the surface secretion or production of the DraE adhesin.
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