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  • Artikel: DFG Deutsche Nationallizenzen  (23)
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  • Artikel: DFG Deutsche Nationallizenzen  (23)
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  • 1
    Digitale Medien
    Digitale Medien
    Chromosomal insertion and excision of a 30 kb unstable genetic element is responsible for phase variation of lipopolysaccharide and other virulence determinants in Legionella pneumophila (2001)
    Oxford, UK : Blackwell Science, Ltd
    Molecular microbiology 39 (2001), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: We recently described the phase-variable expression of a virulence-associated lipopolysaccharide (LPS) epitope in Legionella pneumophila. In this study, the molecular mechanism for phase variation was investigated. We identified a 30 kb unstable genetic element as the molecular origin for LPS phase variation. Thirty putative genes were encoded on the 30 kb sequence, organized in two putative opposite transcription units. Some of the open reading frames (ORFs) shared homologies with bacteriophage genes, suggesting that the 30 kb element was of phage origin. In the virulent wild-type strain, the 30 kb element was located on the chromosome, whereas excision from the chromosome and replication as a high-copy plasmid resulted in the mutant phenotype, which is characterized by alteration of an LPS epitope and loss of virulence. Mapping and sequencing of the insertion site in the genome revealed that the chromosomal attachment site was located in an intergenic region flanked by genes of unknown function. As phage release could not be induced by mitomycin C, it is conceivable that the 30 kb element is a non-functional phage remnant. The protein encoded by ORF T on the 30 kb plasmid could be isolated by an outer membrane preparation, indicating that the genes encoded on the 30 kb element are expressed in the mutant phenotype. Therefore, it is conceivable that the phenotypic alterations seen in the mutant depend on high-copy replication of the 30 kb element and expression of the encoded genes. Excision of the 30 kb element from the chromosome was found to occur in a RecA-independent pathway, presumably by the involvement of RecE, RecT and RusA homologues that are encoded on the 30 kb element.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.2001.02314.x
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  • 2
    Digitale Medien
    Digitale Medien
    Fibronectin mediates Opc-dependent internalization of Neisseria meningitidis in human brain microvascular endothelial cells (2002)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 46 (2002), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: A central step in the pathogenesis of bacterial meningitis caused by Neisseria meningitidis (the meningococcus) is the interaction of the bacteria with cells of the blood–brain barrier. In the present study, we analysed the invasive potential of two strains representing hypervirulent meningococcal lineages of the ET-5 and ET-37 complex in human brain-derived endothelial cells (HBEMCs). In contrast to previous observations made with epithelial cells and human umbilical vein-derived endothelial cells (HUVECs), significant internalization of encapsulated meningococci by HBMECs was observed. However, this uptake was found only for the ET-5 complex isolate MC58, and not for an ET-37 complex strain. Furthermore, the uptake of meningococci by HBMECs depended on the presence of human serum, whereas serum of bovine origin did not promote the internalization of meningococci in HBMECs. By mutagenesis experiments, we demonstrate that internalization depended on the expression of the opc gene, which is present in meningococci of the ET-5 complex, but absent in ET-37 complex meningococci. Chromatographic separation of human serum proteins revealed fibronectin as the uptake-promoting serum factor, which binds to HBMECs via α5β1 integrin receptors. These data provide evidence for unique molecular mechanisms of the interaction of meningococci with endothelial cells of the blood–brain barrier and contribute to our understanding of the pathogenesis of meningitis caused by meningococci of different clonal lineages.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2958.2002.03222.x
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  • 3
    Digitale Medien
    Digitale Medien
    Phospholipid substitution of capsular polysaccharides and mechanisms of capsule formation in Neisseria meningitidis (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 8 (1993), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Within the capsule gene complex (cps) of Neisseria meningitidis two functional regions B and C are involved in surface translocation of the cytoplasmically synthesized capsular polysaccharide, which is a homopolymer of α-2,8 polyneuraminic acid. The region-C gene products share characteristics with transporter proteins of the ABC (ATP-binding cassette) superfamily of active transporters. For analysis of the role of region B in surface translocation of the capsular polysaccharide we purified the polysaccharides of region B- and region C-defective Escherichia coli clones by affinity chromatography. The molecular weights of the polysaccharides were determined by gel filtration and the polysaccharides were analysed for phospholipid substitution by polyacrylamide gel electrophoresis and immunoblotting. The results indicate that the full-size capsular polysaccharide with a phospholipid anchor is synthesized intracellularly and that lipid modification is a strong requirement for translocation of the poly saccharide to the cell surface. Proteins encoded by region B are involved in phospholipid substitution of the capsular polysaccharide. Nucleotide sequence analysis of region B revealed two open reading frames, which encode proteins with molecular masses of 45.1 and 48.7 kDa.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb01592.x
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  • 4
    Digitale Medien
    Digitale Medien
    The role of galE in the biosynthesis and function of gonococcal lipopolysaccharide (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 8 (1993), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Lipopolysaccharide is an essential component of the outer membrane of Gram-negative bacteria and an important virulence factor of many pathogens, such as Neisseria gonorrhoeae. We have cloned the gonococcal galE gene which was found to be located in the gonococcal homologue of the meningococcal capsule gene complex region D. Sequence alignment indicated extensive homology with the Escherichia coli and Salmonella GalE proteins. Mutants with insertions in the galE gene were used as a tool to characterize the structure and function of gonococcal lipopolysaccharide. They displayed deep rough phenotypes, and chemical analysis confirmed the loss of galactose from the mutant lipopolysaccharide. Functional analysis indicated that the terminal oligosaccharides contain galactose and that these are lost in galE mutants. The importance of these oligosaccharides in gonococcal biology is clear from the fact that they contain the epitopes that are the targets for killing by normal human serum, and the acceptor site for sialic acid, which acts to protect the gonococcus from this killing. Furthermore, infection experiments in vitro indicate that the galE mutants exhibit unaltered intergonococcal adhesion as well as adhesion to, and invasion of, epithelial cells.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb01635.x
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  • 5
    Digitale Medien
    Digitale Medien
    Molecular analysis of the biosynthesis pathway of the α-2,8 polysialic acid capsule by Neisseria meningitidls serogroup B (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 14 (1994), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: The genes encoding all enzymes necessary for capsular polysaccharide biosynthesis in Neisseria meningitidis B are located on a 5 kb DNA fragment within the chromosomal cps gene cluster. Nucleotide sequence analysis revealed four open reading frames (ORFs), which can encode proteins with molecular masses of 41.4 kDa, 24.9kDa, 38.3 kDa, and 54.4 kDa, respectively. These ORFs constitute a transcriptional unit as demonstrated by Northern blots. Primer extension analysis revealed that the transcriptional start site is preceded by a nucleotide sequence with homologies to the σ70consensus promoter sequence of Escherichia coli. Functional analysis of the proteins encoded by the ORFs indicated that ORF2 encodes the CMP-NeuNAc synthetase, ORF3 encodes the NeuNAc condensing enzyme, and ORF4 encodes the α-2,8 polysialyltransferase. ORF1 encodes an enzyme, which provides a precursor molecule for synthesis of monomeric NeuNAc. In E. coli the subcloned ORFs 2–4 were able to synthesize a high-molecular-weight α-2,8 polysialic acid. In contrast, inactivation of ORF1 in the meningococcal genome resulted in a complete loss of capsule production. A regulatory enzyme, the CMP-NeuNAc hydrolase, which cleaves CMP-NeuNAc to CMP and NeuNAc, was not found as a part of the capsular polysaccharide biosynthesis gene operon or within the cps gene cluster.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.1994.tb01274.x
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  • 6
    Digitale Medien
    Digitale Medien
    Contribution of genes from the capsule gene complex (cps) to lipooligosaccharide biosynthesis and serum resistance in Neisseria meningitidis (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 11 (1994), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Within the capsule gene complex (cps) of Neisseria meningitidis B a 5.5 kb DNA fragment encodes proteins with strong homologies to enzymes of the lipopolysaccharide biosynthetic pathway of Salmonella typhimurium and Escherichia coli, GalE, RfbB, RfbC and RfbD. A meningococcal galE mutant expressed a truncated lipooligosaccharide (LOS), which terminated at the glucose residue between inner and outer core, and a second gaiE gene present outside the cps cluster was found to be transcriptionally and functionally inactive and, thus, unable to complement this defect. Because of the defect in the outer core, the LOS of the galE-defective meningococcal mutant was not sialylated. In contrast, carbohydrate analysis of the LOS of an rfb-defective meningococcal mutant revealed no difference from the LOS of the wild-type strain, suggesting that the rfb genes are inactive. This was supported by Northern blot analysis, which showed that expression of the rfb gene products was transcriptionally regulated. The inability of the meningococcal galE mutant, which cannot sialylate the LOS, allowed us to investigate the significance of LOS sialylation in relation to the presence of the polysialic acid capsule. Sialylated LOS, but not the polysialic acid capsule, is necessary to confer complete serum resistance on the meningococcus by inhibition of the alternative complement pathway.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.1994.tb00367.x
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  • 7
    Digitale Medien
    Digitale Medien
    Mechanisms of neisserial serum resistance (1999)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 32 (1999), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Pathogenic Neisseria use a variety of mechanisms to survive the bactericidal action of the complement system. Serum resistance is a crucial virulence factor for the development of severe meningococcal disease, meningococcal meningitis and disseminated gonococcal infection. Furthermore, local inflammation at the site of gonococcal infection exposes the bacteria to moderate concentrations of complement factors. We review current concepts of neisserial serum resistance with emphasis on porins and polysaccharides exposed on the neisserial surface and their interaction with components of normal human serum.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2958.1999.01469.x
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  • 8
    Digitale Medien
    Digitale Medien
    Neisseria meningitidis producing the Opc adhesin binds epithelial cell proteoglycan receptors (1998)
    Oxford BSL : Blackwell Science Ltd, UK
    Molecular microbiology 27 (1998), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Neisseria meningitidis possesses a repertoire of surface adhesins that promote bacterial adherence to and entry into mammalian cells. Here, we have identified heparan sulphate proteoglycans as epithelial cell receptors for the meningococcal Opc invasin. Binding studies with radiolabelled heparin and heparin affinity chromatography demonstrated that Opc is a heparin binding protein. Subsequent binding experiments with purified 35SO4-labelled epithelial cell proteoglycan receptors and infection assays with epithelial cells that had been treated with heparitinase to remove glycosaminoglycans confirmed that Opc-expressing meningococci exploit host cell-surface proteoglycans to gain access to the epithelial cell interior. Unexpectedly, Opa28-producing meningococci lacking Opc also bound proteoglycans. These bacteria also bound CEA receptors in contrast to the Opc-expressing phenotype, suggesting that Opa28 may possess domains with specificity for different receptors. Opa/Opc-negative meningococci did not bind either proteoglycan or CEA receptors. Using a set of genetically defined mutants with different lipopolysaccharide (LPS) and capsular phenotype, we were able to demonstrate that surface sialic acids interfere with the Opc–proteoglycan receptor interaction. This effect may provide the molecular basis for the reported modulatory effect of capsule and LPS on meningococcal adherence to and entry into various cell types.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2958.1998.00763.x
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  • 9
    Digitale Medien
    Digitale Medien
    Capsule phase variation in Neisseria meningitidis serogroup B by slipped-strand mispairing in the polysialyltransferase gene (siaD): correlation with bacterial invasion and the outbreak of meningococcal disease (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 20 (1996), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: A mechanism of capsular polysaccharide phase variation in Neisseria meningitidis is described. Meningococcal cells of an encapsulated serogroup B strain were used in invasion assays. Only unencapsulated variants were found to enter epithelial cells. Analysis of one group of capsule-deficient variants indicated that the capsular polysaccharide was re-expressed at a frequency of 10−3. Measurement of enzymatic activities involved in the biosynthesis of the α-2,8 polysialic acid capsule showed that polysialyltransferase (PST) activity was absent in these capsule-negative variants. Nucleotide sequence analysis of siaD revealed an insertion or a deletion of one cytidine residue within a run of (dC)7 residues at position 89, resulting in a frameshift and premature termination of translation. We analysed unencapsulated isolates from carriers and encapsulated case isolates collected during an outbreak of meningococcal disease. Further paired blood-culture isolates and unencapsulated nasopharyngeal isolates from patients with meningococcal meningitis were examined. In all unencapsulated strains analysed we found an insertion or deletion within the oligo-(dC) stretch within siaD, resulting in a frameshift and loss of capsule formation. All encapsulated isolates, however, had seven dC residues at this position, indicating a correlation between capsule phase variation and bacterial invasion and the out-break of meningococcal disease.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.1996.tb02641.x
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  • 10
    Digitale Medien
    Digitale Medien
    Molecular cloning and functional expression of bacteriophage PK1E-encoded endoneuraminidase Endo NE (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 16 (1995), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Homopolymeric α-2,8-linked sialic acid (PSA) has been found as a capsular component of sepsis- and meningitis-causing bacterial pathogens, and on eukaryotic cells as a post-translational modification of the neural cell adhesion molecule (NCAM). The polysaccharide is specifically recognized and degraded by a phage-encoded enzyme, the endo-N-acetylneuraminidase E (Endo NE). Endo NE therefore has become a valuable tool in the study of bacterial pathogenesis and eukaryotic morphogenesis. In this report we describe the molecular cloning of Endo NE and the expression of a functionally active recombinant enzyme. The cloned DNA sequence (2436 bp) encodes a polypeptide of 811 amino acids, which at the 5′ end contains a totally conserved neuraminidase motif. Expressed in Escherichia coli, the enzyme migrates as a single band of approximately 74 kDa in SDS-PAGE. A central domain of 669 amino acid residues is about 90% homologous to the recently cloned Endo NF. Both phage-induced lysis of bacteria and the catalysis of PSA degradation by the recombinant enzyme are efficiently inhibited by a polyclonal antiserum raised against the intact phage particle. The C-terminal region seems to be essential to enzymatic functions, as truncation of 32 amino acids outside the homology domain completely abolishes Endo NE activity. Our data also indicate that the 38 kDa protein, previously assumed to be a subunit of the Endo NE holoenzyme, is the product of a separate gene locus and is not necessary for in vitro depolymerase activity.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.1995.tb02409.x
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