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Sökning: L773:1365 2958 > Engelska

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1.
  • Ahuja, Umesh, et al. (författare)
  • Haem-delivery proteins in cytochrome c maturation System II
  • 2009
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 73:6, s. 1058-1071
  • Tidskriftsartikel (refereegranskat)abstract
    • P>Cytochromes of the c-type function on the outer side of the cytoplasmic membrane in bacteria where they also are assembled from apo-cytochrome polypeptide and haem. Two distinctly different systems for cytochrome c maturation are found in bacteria. System I present in Escherichia coli has eight to nine different Ccm proteins. System II is found in Bacillus subtilis and comprises four proteins: CcdA, ResA, ResB and ResC. ResB and ResC are poorly understood polytopic membrane proteins required for cytochrome c synthesis. We have analysed these two B. subtilis proteins produced in E. coli and in the native organism. ResB is shown to bind protohaem IX and haem is found covalently bound to residue Cys-138. Results in B. subtilis suggest that also ResC can bind haem. Our results complement recent findings made with Helicobacter CcsBA supporting the hypothesis that ResBC as a complex translocates haem by attaching it to ResB on the cytoplasmic side of the membrane and then transferring it to an extra-cytoplasmic location in ResC, from where it is made available to the apo-cytochromes.
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2.
  • Ausmees, Nora, et al. (författare)
  • SmeA, a small membrane protein with multiple functions in Streptomyces sporulation including targeting of a SpoIIIE/FtsK-like protein to cell division septa
  • 2007
  • Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 65:6, s. 1458-1473
  • Tidskriftsartikel (refereegranskat)abstract
    • Sporulation in aerial hyphae of Streptomyces coelicolor involves profound changes in regulation of fundamental morphogenetic and cell cycle processes to convert the filamentous and multinucleoid cells to small unigenomic spores. Here, a novel sporulation locus consisting of smeA (encoding a small putative membrane protein) and sffA (encoding a SpoIIIE/FtsK-family protein) is characterized. Deletion of smeA-sffA gave rise to pleiotropic effects on spore maturation, and influenced the segregation of chromosomes and placement of septa during sporulation. Both smeA and sffA were expressed specifically in apical cells of sporogenic aerial hyphae simultaneously with or slightly after Z-ring assembly. The presence of smeA-like genes in streptomycete chromosomes, plasmids and transposons, often paired with a gene for a SpoIIIE/FtsK- or Tra-like protein, indicates that SmeA and SffA functions might be related to DNA transfer. During spore development SffA accumulated specifically at sporulation septa where it colocalized with FtsK. However, sffA did not show redundancy with ftsK, and SffA function appeared distinct from the DNA translocase activity displayed by FtsK during closure of sporulation septa. The septal localization of SffA was dependent on SmeA, suggesting that SmeA may act as an assembly factor for SffA and possibly other proteins required during spore maturation.
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3.
  • Berggård, Karin, et al. (författare)
  • Binding of human C4BP to the hypervariable region of M protein: a molecular mechanism of phagocytosis resistance in Streptococcus pyogenes
  • 2001
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 42:2, s. 539-551
  • Tidskriftsartikel (refereegranskat)abstract
    • The amino-terminal hypervariable region (HVR) of streptococcal M protein is required for the ability of this virulence factor to confer phagocytosis resistance. The function of the HVR has remained unknown, but the finding that many HVRs with extremely divergent sequences bind the human complement regulator C4b-binding protein (C4BP) has suggested that this ligand may play a role in phagocytosis resistance. We used the M22 system to study the function of bound C4BP and provide several lines of evidence that C4BP indeed contributes to phagocytosis resistance. First, the ability of anti-HVR antibodies to cause opsonization correlated with their ability to inhibit binding of C4BP. Secondly, a short deletion in the HVR eliminated C4BP binding and also reduced the ability of M22 to confer phagocytosis resistance. Thirdly, the addition of an excess of pure C4BP to a phagocytosis system almost completely blocked the effect of opsonizing anti-HVR antibodies. Together, our data indicate that binding of C4BP to the HVR of M22 plays an important role in phagocytosis resistance, but other properties of M22 also contribute. This study provides the first molecular insight into the mechanisms by which the HVR of an M protein confers phagocytosis resistance.
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4.
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5.
  • Frick, Inga-Maria, et al. (författare)
  • Uptake and intracellular transportation of a bacterial surface protein in lymphoid cells.
  • 2002
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 44:4, s. 917-934
  • Tidskriftsartikel (refereegranskat)abstract
    • Some strains of the human pathogen Streptococcus pyogenes express a surface protein called protein H, which is released from the streptococcal surface by a cysteine proteinase produced by the bacteria. Here, we find that soluble protein H binds to the surface of lymphocytes and granulocytes, and that the molecule is taken up by lymphocytes and transported to the perinuclear region. The translocation over the cell membrane is rapid, and the uptake and intracellular transportation is not dependent on actin polymerization. Protein H could be immunoprecipitated from cell extracts and nuclear preparations of lymphocytes, and analysis of molecular interactions between pro-tein H and proteins of different cellular compart-ments demonstrated a binding to nucleophosmin/ B23, a protein known to shuttle between the cytoplasm and the nucleus, and to the nuclear proteins SET and hnRNP A2/B1. Nucleophosmin/B23 was co-immunoprecipitated with protein H from cell and nuclear extracts, and binding experiments, including kinetic analyses, suggest that protein H dissociating from nucleophosmin/B23 complexes in the perinuclear region or in the nucleus binds to proteins SET and hnRNP A2/B1. Finally, the uptake and intracellular transportation of protein H was found to result in a cytostatic effect on B and T lymphocytes.
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6.
  • Frick, Inga-Maria, et al. (författare)
  • Virulent aggregates of Streptococcus pyogenes are generated by homophilic protein-protein interactions
  • 2000
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 37:5, s. 1232-1247
  • Tidskriftsartikel (refereegranskat)abstract
    • Many strains of the important human pathogen Streptococcus pyogenes form aggregates when grown in vitro in liquid medium. The present studies demonstrate that this property is crucial for the adherence, the resistance to phagocytosis and the virulence of S. pyogenes. A conserved sequence of 19 amino acid residues (designated AHP) was identified in surface proteins of common S. pyogenes serotypes. This sequence was found to promote bacterial aggregation through homophilic protein-protein interactions between AHP-containing surface proteins of neighbouring bacteria. A synthetic AHP peptide inhibited S. pyogenes aggregation, reduced the survival of S. pyogenes in human blood and attenuated its virulence in mice. In contrast, mutant bacteria devoid of surface proteins containing AHP-related sequences did not aggregate or adhere to epithelial cells. These bacteria are also rapidly killed in human blood and show reduced virulence in mice, underlining the pathogenic significance of the AHP sequence and S. pyogenes aggregation.
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7.
  • Hedlund, Maria, et al. (författare)
  • Sphingomyelin, glycosphingolipids, and ceramide signalling in cells exposed to p-fimbriated Escherichia coli
  • 1998
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 29:5, s. 1297-1306
  • Forskningsöversikt (refereegranskat)abstract
    • Uropathogenic Escherichia coli attach to epithelial cells through P fimbriae that bind Galα1‐4Galβ‐oligosaccharide sequences in cell surface glycosphingolipids. The binding of P‐fimbriated E. coli to uroepithelial cells causes the release of ceramide, activation of the ceramide signalling pathway and a cytokine response in the epithelial cells. The present study examined the molecular source of ceramide in human kidney A498 cells exposed to P‐fimbriated E. coli. Agonists such as TNF‐α and IL‐1β released ceramide from sphingomyelin by the activation of endogenous sphingomyelinases and hydrolysis of sphingomyelin, and triggered an IL‐6 response. P‐fimbriated E. coli caused a slight increase in endogenous sphingomyelinase activity, but there was no associated sphingomyelin hydrolysis. Instead, the concentration of galactose‐containing glycolipids decreased. We propose that P‐fimbriated E. coli differ from other activators of the ceramide pathway, in that release of ceramide is from receptor glycolipids and not from sphingomyelin. Receptor breakdown may be an efficient host defence strategy, as it reduces the concentration of cell surface receptors, releases soluble receptor analogues and activates an inflammatory response.
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8.
  • Hedlund, Maria, et al. (författare)
  • Type 1 fimbriae deliver an LPS- and TLR4-dependent activation signal to CD14-negative cells
  • 2001
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 39:3, s. 542-552
  • Tidskriftsartikel (refereegranskat)abstract
    • Fimbriae target bacteria to different mucosal surfaces and enhance the inflammatory response at these sites. Inflammation may be triggered by the fimbriae themselves or by fimbriae-dependent delivery of other host activating molecules such as lipopolysaccharide (LPS). Although LPS activates systemic inflammation through the CD14 and Toll-like receptor 4 (TLR4) pathways, mechanisms of epithelial cell activation by LPS are not well understood. These cells lack CD14 receptors and are unresponsive to pure LPS, but fimbriated Escherichia coli overcome this refractoriness and trigger epithelial cytokine responses. We now show that type 1 fimbriae can present an LPS- and TLR4-dependent signal to the CD14-negative epithelial cells. Human uroepithelial cells were shown to express TLR4, and type 1 fimbriated E. coli strains triggered an LPS-dependent response in those cells. A similar LPS- and fimbriae-dependent response was observed in the urinary tract of TLR4-proficient mice, but not in TLR4-defective mice. The moderate inflammatory response in the TLR4-defective mice was fimbriae dependent but LPS independent. The results demonstrate that type 1 fimbriae present LPS to CD14-negative cells and that the TLR4 genotype determines this response despite the absence of CD14 on the target cells. The results illustrate how the host "sees" LPS and other microbial products not as purified molecules but as complexes, and that fimbriae determine the molecular context in which LPS is presented to host cells.
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9.
  • Håkansson, Anders P, et al. (författare)
  • A folding variant of alpha-lactalbumin with bactericidal activity against Streptococcus pneumoniae
  • 2000
  • Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 35:3, s. 589-600
  • Tidskriftsartikel (refereegranskat)abstract
    • This study describes an alpha-lactalbumin folding variant from human milk with bactericidal activity against antibiotic-resistant and -susceptible strains of Streptococcus pneumoniae. The active complex precipitated with the casein fraction at pH 4.6 and was purified from casein by a combination of anion exchange and gel chromatography. Unlike other casein components, the active complex was retained on the ion-exchange matrix and eluted only with high salt. The eluted fraction showed N-terminal and mass spectrometric identity with human milk alpha-lactalbumin, but native alpha-lactalbumin had no bactericidal effect. Spectroscopic analysis demonstrated that the active form of the molecule was in a different folding state, with secondary structure identical to alpha-lactalbumin from human milk whey, but fluctuating tertiary structure. Native alpha-lactalbumin could be converted to the active bactericidal form by ion-exchange chromatography in the presence of a cofactor from human milk casein, characterized as a C18:1 fatty acid. Analysis of the antibacterial spectrum showed selectivity for streptococci; Gram-negative and other Gram-positive bacteria were resistant. The folding variant of alpha-lactalbumin is a new example of naturally occurring molecules with antimicrobial activity.
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10.
  • Krokowski, D, et al. (författare)
  • Yeast ribosomal P0 protein has two separate binding sites for P1/P2 proteins
  • 2006
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 60:2, s. 386-400
  • Tidskriftsartikel (refereegranskat)abstract
    • The ribosome has a distinct lateral protuberance called the stalk; in eukaryotes it is formed by the acidic ribosomal P-proteins which are organized as a pentameric entity described as P0-(P1-P2)(2). Bilateral interactions between P0 and P1/P2 proteins have been studied extensively, however, the region on P0 responsible for the binding of P1/P2 proteins has not been precisely defined. Here we report a study which takes the current knowledge of the P0 - P1/P2 protein interaction beyond the recently published information. Using truncated forms of P0 protein and several in vitro and in vivo approaches, we have defined the region between positions 199 and 258 as the P0 protein fragment responsible for the binding of P1/P2 proteins in the yeast Saccharomyces cerevisiae. We show two short amino acid regions of P0 protein located at positions 199-230 and 231-258, to be responsible for independent binding of two dimers, P1A-P2B and P1B-P2A respectively. In addition, two elements, the sequence spanning amino acids 199-230 and the P1A-P2B dimer were found to be essential for stalk formation, indicating that this process is dependent on a balance between the P1A-P2B dimer and the P0 protein.
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