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Sökning: L773:0950 382X OR L773:1365 2958

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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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11.
  • Larsson, Jonas, et al. (författare)
  • YjbH is a novel negative effector of the disulphide stress regulator,Spx, in Bacillus subtilis.
  • 2007
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 66:3, s. 669-684
  • Tidskriftsartikel (refereegranskat)abstract
    • In the soil bacterium Bacillus subtilis Spx is a key regulator that controls expression, positively or negatively, of several genes in response to certain oxidative stresses that lead to the formation of unwanted disulphide bonds. Here we characterized the yjbH gene and show that it encodes a novel effector of Spx. The yjbH gene is part of the yjbIH operon that encodes a truncated haemoglobin (YjbI) and a predicted 34 kDa cytosolic protein of unknown function (YjbH). Deletion of yjbIH or yjbH has pleiotropic effects and affects growth, sporulation and competence development. Cells lacking yjbIH display a reduced sensitivity to the thiol oxidant diamide and show an apparent down- or upregulation of several transcripts that belong to the Spx regulon. Twenty-two suppressor mutations that bypass the defects conferred by yjbH were isolated. These mutations were identified as six deletions, three nonsense and 11 missense substitutions in the spx gene. Real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis showed that mutations in yjbIH or yjbH do not affect the level of spx transcription. The combined data from the present work show that strains lacking yjbIH or yjbH overproduce Spx under unperturbed growth. The elevated Spx concentration cannot be attributed to an increased spx expression but is likely to result from control at the post-transcriptional level. YjbH is proposed to affect the cellular concentration of Spx by modulating proteolysis via the ClpXP protease.
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12.
  • Lind, Peter A, et al. (författare)
  • Compensatory gene amplification restores fitness after inter-species gene replacements
  • 2010
  • Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 75:5, s. 1078-1089
  • Tidskriftsartikel (refereegranskat)abstract
    • Genes introduced by gene replacements and other types of horizontal gene transfer (HGT) represent a significant presence in many archaeal and eubacterial genomes. Most alien genes are likely to be neutral or deleterious upon arrival and their long-term persistence may require a mechanism that improves their selective contribution. To examine the fate of inter-species gene replacements, we exchanged three native S. typhimurium genes encoding ribosomal proteins with orthologues from various other microbes. The results show that replacement of each of these three genes reduces fitness to such an extent that it would provide an effective barrier against inter-species gene replacements in eubacterial populations. However, these fitness defects could be partially ameliorated by gene amplification that augmented the dosage of the heterologous proteins. This suggests that suboptimal expression is a common fitness constraint for inter-species gene replacements, with fitness costs conferred by either a lower expression level of the alien protein compared with the native protein or a requirement for an increased amount of the alien protein to maintain proper function. Our findings can explain the observation that duplicated genes are over-represented among horizontally transferred genes, and suggest a potential coupling between compensatory gene amplification after HGT and the evolution of new genes.
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13.
  • Liu, Yiming, et al. (författare)
  • Penicillin-binding protein SpoVD disulfide is a target for StoA in Bacillus subtilis forespores.
  • 2010
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 75:1, s. 46-60
  • Tidskriftsartikel (refereegranskat)abstract
    • Summary The bacterial endospore is a dormant and heat-resistant form of life. StoA (SpoIVH) in Bacillus subtilis is a membrane-bound thioredoxin-like protein involved in endospore cortex synthesis. It is proposed to reduce disulfide bonds in hitherto unknown proteins in the inter-membrane compartment of developing forespores. Starting with a bioinformatic analysis combined with mutant studies we identified the sporulation-specific, high molecular weight, class B penicillin-binding protein SpoVD as a putative target for StoA. We then demonstrate that SpoVD is a membrane-bound protein with two exposed redox-active cysteine residues. Structural modelling of SpoVD, based on the well characterized orthologue PBP2x of Streptococcus pneumoniae, confirmed that a disulfide bond can form close to the active site of the penicillin-binding domain restricting access of enzyme substrate or functional association with other cortex biogenic proteins. Finally, by exploiting combinations of mutations in the spoVD, stoA and ccdA genes in B. subtilis cells, we present strong in vivo evidence that supports the conclusion that StoA functions to specifically break the disulfide bond in the SpoVD protein in the forespore envelope. The findings contribute to our understanding of endospore biogenesis and open a new angle to regulation of cell wall synthesis and penicillin-binding protein activity.
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14.
  • Nilsson, Maria, et al. (författare)
  • The antibacterial activity of peptides derived from human beta-2 glycoprotein I is inhibited by protein H and M1 protein from Streptococcus pyogenes.
  • 2008
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 67:3, s. 482-492
  • Tidskriftsartikel (refereegranskat)abstract
    • During the last years, the importance of antibacterial peptides has attracted considerable attention. We report here that peptides derived from the fifth domain of beta-2 glycoprotein I (beta(2)GPI), a human heparin binding plasma protein, have antibacterial activities against Gram-positive and Gram-negative bacteria. Streptococcus pyogenes, an important human pathogen that can survive and grow in human blood, has developed mechanisms to escape the attack by these peptides. Thus, protein H and M1 protein, two surface proteins of the highly pathogenic S. pyogenes AP1 strain, bind full-length beta(2)GPI and thereby prevent the processing of beta(2)GPI by proteases from polymorphonuclear neutrophils (PMNs) into antibacterial peptides. In addition, protein H and M1 protein, released from the bacterial cell wall by PMN-derived proteases, bind to, and inhibit the activity of, beta(2)GPI-derived antibacterial peptides. Taken together, the data suggest that the interaction between the streptococcal proteins and beta(2)GPI or beta(2)GPI-derived peptides presents a novel mechanism to resist an antibacterial attack by beta(2)GPI-cleavage products.
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15.
  • Piskur, Jure, et al. (författare)
  • Yeast genome sequencing: the power of comparative genomics
  • 2004
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 53:2, s. 381-389
  • Forskningsöversikt (refereegranskat)abstract
    • For decades, unicellular yeasts have been general models to help understand the eukaryotic cell and also our own biology. Recently, over a dozen yeast genomes have been sequenced, providing the basis to resolve several complex biological questions. Analysis of the novel sequence data has shown that the minimum number of genes from each species that need to be compared to produce a reliable phylogeny is about 20. Yeast has also become an attractive model to study speciation in eukaryotes, especially to understand molecular mechanisms behind the establishment of reproductive isolation. Comparison of closely related species helps in gene annotation and to answer how many genes there really are within the genomes. Analysis of non-coding regions among closely related species has provided an example of how to determine novel gene regulatory sequences, which were previously difficult to analyse because they are short and degenerate and occupy different positions. Comparative genomics helps to understand the origin of yeasts and points out crucial molecular events in yeast evolutionary history, such as whole-genome duplication and horizontal gene transfer(s). In addition, the accumulating sequence data provide the background to use more yeast species in model studies, to combat pathogens and for efficient manipulation of industrial strains.
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16.
  • Rasmussen, Magnus, et al. (författare)
  • Proteolysis and its regulation at the surface of Streptococcus pyogenes.
  • 2002
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 43:3, s. 537-544
  • Forskningsöversikt (refereegranskat)abstract
    • Pathogenic bacteria often produce proteinases that are believed to be involved in virulence. Moreover, several host defence systems depend on proteolysis, demonstrating that proteolysis and its regulation play an important role during bacterial infections. Here, we discuss how proteolytical events are regulated at the surface of Streptococcus pyogenes during infection with this important human pathogen. Streptococcus pyogenes produces proteinases, and host proteinases are produced and released as a result of the infection. Streptococcus pyogenes also recruits host proteinase inhibitors to its surface, suggesting that proteolysis is tightly regulated at the bacterial surface. We propose that the initial phase of a S. pyogenes infection is characterized by inhibition of proteolysis and complement activity at the bacterial surface. This is achieved mainly through binding of host proteinase inhibitors and complement regulatory proteins to bacterial surface proteins. In a later phase of the infection, massive proteolytic activity will release bacterial surface proteins and degrade human tissues, thus facilitating bacterial spread. These proteolytic events are regulated both temporally and spatially, and should influence virulence and the outcome of S. pyogenes infections.
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17.
  • Rasmussen, Magnus, et al. (författare)
  • Unique regulation of SclB - a novel collagen-like surface protein of Streptococcus pyogenes
  • 2001
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 40:6, s. 1427-1438
  • Tidskriftsartikel (refereegranskat)abstract
    • Slipped-strand mispairing at sites containing so-called coding repeats (CRs) can lead to phase variation of surface proteins in Gram-negative bacteria. This mechanism, believed to contribute to virulence, has so far not been identified in a Gram-positive bacterium. In the genome of the Gram-positive human pathogen Streptococcus pyogenes, we identified pentanucleotide CRs within a putative signal sequence of an open reading frame (ORF) encoding a novel collagen-like surface protein, denoted SclB. In 12 S. pyogenes strains, the number of CRs in the sclB gene varied from three to 19, rendering the start codon in frame with the downstream ORF in four strains and out of frame in eight strains. A protein reacting with anti-SclB antibodies could only be solubilized from three strains, all containing an intact sclB gene. Variations in the number of CRs were observed within strains of the same M serotype and occurred during growth of S. pyogenes in fresh human blood, but not in medium. The SclB protein has a hypervariable N-terminal part, a collagen-like central part and a typical cell wall sorting sequence containing the LPXTGX motif. SclB is related to the collagen-like SclA and is, like SclA, involved in the adhesion of S. pyogenes bacteria to human cells. However, the Mga protein, known to upregulate sclA and several additional genes encoding virulence factors of S. pyogenes, downregulates sclB transcription. This observation and the potential of SclB to phase vary by slipped-strand mispairing emphasize the unique regulation of this novel S. pyogenes surface protein.
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18.
  • Sandin, Charlotta, et al. (författare)
  • Binding of human plasma proteins to Streptococcus pyogenes M protein determines the location of opsonic and non-opsonic epitopes
  • 2006
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 59:1, s. 20-30
  • Tidskriftsartikel (refereegranskat)abstract
    • Antibodies directed against a pathogenic microorganism may recognize either protective or non-protective epitopes. Because antibodies elicited by a vaccine must be directed against protective epitopes, it is essential to understand the molecular properties that distinguish the two types of epitope. Here we analyse this problem for the antiphagocytic M protein of Streptococcus pyogenes, using the opsonizing capacity of antibodies to estimate their ability to confer protection in vivo. Our studies were focused on the M5 protein, which has three surface-exposed regions: the amino-terminal hypervariable region (HVR) and the B- and C-repeat regions. We first analysed the role of different M5 regions in phagocytosis resistance under non-immune conditions, employing chromosomal mutants expressing M5 proteins with internal deletions, and demonstrate that only the B-repeat region is essential for phagocytosis resistance. However, only antibodies to the HVR were opsonic. This apparent paradox could be explained by the ability of fibrinogen and albumin to specifically bind to the B- and C-repeats, respectively, causing inhibition of antibody binding under physiological conditions, while antibodies to the HVR could bind and promote deposition of complement. These data indicate that binding of human plasma proteins plays an important role in determining the location of opsonic and non-opsonic epitopes in streptococcal M protein.
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19.
  • Schmidtchen, Artur, et al. (författare)
  • Dermatan sulphate is released by proteinases of common pathogenic bacteria and inactivates antibacterial alpha-defensin
  • 2001
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 39:3, s. 708-713
  • Tidskriftsartikel (refereegranskat)abstract
    • Defensins represent an evolutionarily conserved group of small peptides with potent antibacterial activities. We report here that extracellular proteinases secreted by the human pathogens Pseudomonas aeruginosa, Enterococcus faecalis and Streptococcus pyogenes release dermatan sulphate by degrading dermatan sulphate-containing proteoglycans, such as decorin. Dermatan sulphate was found to bind to neutrophil-derived alpha-defensin, and this binding completely neutralized its bactericidal activity. During infection, proteoglycan degradation and release of dermatan sulphate may therefore represent a previously unknown virulence mechanism, which could serve as a target for novel antibacterial strategies.
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20.
  • Singh, Birendra, et al. (författare)
  • Vitronectin binds to the head region of Moraxella catarrhalis ubiquitous surface protein A2 and confers complement-inhibitory activity.
  • 2010
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 75, s. 1426-1444
  • Tidskriftsartikel (refereegranskat)abstract
    • Summary The serum resistance of the common respiratory pathogen Moraxella catarrhalis is mainly dependent on ubiquitous surface proteins (Usp) A1 and A2 that interact with complement factor 3 (C3) and complement inhibitor C4b binding protein (C4BP) preventing the alternative and classical pathways of the complement system respectively. UspA2 also has the capacity to attract vitronectin that in turn binds C9 and hereby inhibits membrane attack complex (MAC) formation. We found UspA2 as a major vitronectin binding protein and hence the UspA2/vitronectin interaction was studied in detail. The affinity constant (K(D)) for vitronectin binding to UspA2 was 2.3 x 10(-8) M, and the N-terminal region encompassing residues UspA2 30-170 bound vitronectin with a K(D) of 7.9 x 10(-8) M. Electron microscopy verified that the active binding domain (UspA2(30-177)) was located at the head region of UspA2. Experiments with recombinantly expressed vitronectin also revealed that UspA2(30-177) bound to the C-terminal region of vitronectin residues 312-396. Finally, when human serum was pre-incubated with UspA2, bacteria showed significantly less serum resistance. Our study directly reveals the binding mode between the N-terminal domain of UspA2 and the C-terminal part of vitronectin and thus sheds light upon the mechanism of M. catarrhalis-dependent serum resistance.
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21.
  • Thorsen, Michael, 1974, et al. (författare)
  • Glutathione serves an extracellular defence function to decrease arsenite accumulation and toxicity in yeast.
  • 2012
  • Ingår i: Molecular microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 84:6, s. 1177-88
  • Tidskriftsartikel (refereegranskat)abstract
    • Arsenic is an environmental toxin and a worldwide health hazard. Since this metalloid is ubiquitous in nature, virtually all living organisms require systems for detoxification and tolerance acquisition. Here, we show that during chronic exposure to arsenite [As(III)], Saccharomyces cerevisiae (budding yeast) exports and accumulates the low-molecular-weight thiol molecule glutathione (GSH) outside of cells. Extracellular accumulation of the arsenite triglutathione complex As(GS)₃ was also detected and direct transport assays demonstrate that As(GS)₃ does not readily enter cells. Yeast cells with increased extracellular GSH levels accumulate less arsenic and display improved growth when challenged with As(III). Conversely, cells defective in export and extracellular accumulation of GSH are As(III) sensitive. Taken together, our data are consistent with a novel detoxification mechanism in which GSH is exported to protect yeast cells from arsenite toxicity by preventing its uptake.
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22.
  • Wang, Ellen, et al. (författare)
  • Structure and functional properties of the Bacillus subtilis transcriptional repressor Rex.
  • 2008
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 69:2, s. 466-478
  • Tidskriftsartikel (refereegranskat)abstract
    • The transcription factor Rex has been implicated in regulation of the expression of genes important for fermentative growth and for growth under conditions of low oxygen tension in several Gram-positive bacteria. Rex senses the redox poise of the cell through changes in the NADH/NAD(+) ratio. The crystal structures of two essentially identical Rex proteins, from Thermus aquaticus and T. thermophilus, have previously been determined in complex with NADH. Here we present the crystal structure of the Rex protein from Bacillus subtilis, as well as extensive studies of its affinity for nucleotides and DNA, using surface plasmon resonance, isothermal titration calorimetry and electrophoretic mobility shift assays. We show that Rex has a very high affinity for NADH but that its affinity for NAD(+) is 20 000 times lower. However the NAD(+) affinity is increased by a factor of 30 upon DNA binding, suggesting that there is a positive allosteric coupling between DNA binding and NAD(+) binding. The crystal structures of two pseudo-apo forms (from crystals soaked with NADH and co-crystallized with ATP) show a very different conformation from the previously determined Rex:NADH complexes, in which the N-terminal domains are splayed away from the dimer core. A mechanism is proposed whereby conformational changes in a C-terminal domain-swapped helix mediate the transition from a flexible DNA-binding form to a locked NADH-bound form incapable of binding DNA.
  •  
23.
  • Wullt, Björn, et al. (författare)
  • P fimbriae enhance the early establishment of Escherichia coli in the human urinary tract
  • 2000
  • Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 38:3, s. 456-464
  • Tidskriftsartikel (refereegranskat)abstract
    • This study examined the role of P fimbriae in the establishment of bacteriuria. Patients (n = 17) were subjected to intravesical inoculation with an asymptomatic bacteriuria strain, Escherichia coli 83972, or its P-fimbriated (pap+/prs+) transformants. As shown by groupwise analysis, the pap+/prs+ transformants established bacteriuria more rapidly than E. coli 83972 (P = 0.021) and required a lower number of inoculations to reach 105 cfu ml-1 (P=0.018). Intraindividual analysis showed that the pap+/prs+ transformants established bacteriuria more rapidly than E. coli 83972 in the patients who subsequently became carriers of both strains. Finally, bacterial establishment was shown to vary with the in vivo expression of P fimbriae. Bacterial counts were higher when P-fimbrial expression was detected than when the pap+/prs+ strain showed a negative phenotype. The results suggested that P fimbriae enhance the establishment of bacteriuria and fulfil the molecular Koch postulates as a colonization factor in the human urinary tract.
  •  
24.
  • Brady, L. Jeannine, et al. (författare)
  • The changing faces of Streptococcus antigen I/II polypeptide family adhesins
  • 2010
  • Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 77:2, s. 276-286
  • Tidskriftsartikel (refereegranskat)abstract
    • Streptococcus mutans antigen I/II (AgI/II) protein was one of the first cell wall-anchored adhesins identified in Gram-positive bacteria. It mediates attachment of S. mutans to tooth surfaces and has been a focus for immunization studies against dental caries. The AgI/II family polypeptides recognize salivary glycoproteins, and are also involved in biofilm formation, platelet aggregation, tissue invasion and immune modulation. The genes encoding AgI/II family polypeptides are found among Streptococcus species indigenous to the human mouth, as well as in Streptococcus pyogenes, S. agalactiae and S. suis. Evidence of functionalities for different regions of the AgI/II proteins has emerged. A sequence motif within the C-terminal portion of Streptococcus gordonii SspB (AgI/II) is bound by Porphyromonas gingivalis, thus promoting oral colonization by this anaerobic pathogen. The significance of other epitopes is now clearer following resolution of regional crystal structures. A new picture emerges of the central V (variable) region, predicted to contain a carbohydrate-binding trench, being projected from the cell surface by a stalk formed by an unusual association between an N-terminal α-helix and a C-terminal polyproline helix. This presentation mode might be important in determining functional conformations of other Gram-positive surface proteins that have adhesin domains flanked by α-helical and proline-rich regions. Ever since dental caries (tooth decay) was first shown to be caused by bacteria, there has been continued interest in developing vaccine or passive immunization protocols for its control or prevention (Lehner et al., 1980). Although dental caries is not fatal, and in developed countries caries is now considered to be largely avoidable through controlled diet and good oral hygiene, there remain significant problems with childhood disease, especially among indigent populations. Consequently, caries is one of the most common worldwide infectious diseases. Therefore, research continues towards employing vaccine formulations comprised of peptide components derived from surface proteins of Streptococcus mutans, a major agent associated with dental caries (Lehner et al., 1975). One of the most promising strategies seems to be delivery of peptides, derived from glucan-binding protein B (GbpB) and antigen I/II (AgI/II) protein, via a mucosal (nasal) route. The GbpB polypeptide binds extracellular glucans, thus promoting co-adhesion of S. mutans cells in the development of dental plaque (Taubman and Nash, 2006). The AgI/II protein (also named P1, SpaP, AgB or PAc) is a major surface protein that functions as an adhesin, attaching S. mutans to the saliva-coated tooth enamel surface (Koga et al., 1990; Kelly et al., 1995). Antibodies against SpaP and GbpB block adherence and co-adhesion, respectively, thus disrupting colonization of the oral cavity by S. mutans (Ma et al., 1990; 1998; Taubman and Nash, 2006). The terminology AgI/II derives from the identification of two major cell wall antigens I and II in S. mutans by Russell et al. (1980), and the subsequent recognition that AgII was a component of AgI. Following the discovery of AgI/II, it became apparent that genes encoding orthologous proteins were widely dispersed among the streptococci (Jenkinson and Demuth, 1997). The viridans Streptococcus AgI/II adhesins range in composition from 1310 to 1653 amino acid (aa) residues, while the Streptococcus agalactiae AgI/II proteins are smaller (826–932 aa residues) (Tettelin et al., 2005). The widespread distribution of these AgI/II protein genes across the streptococci is perhaps not surprising, given the complex streptococcal communities that exist on surfaces of the oro- and naso-pharynx and within the bacterial soup of saliva. It is interesting, though, that the AgI/II family polypeptide genes have not yet been discovered in Streptococcus pneumoniae, which might be by the fact that S. pneumoniae forms a distinct evolutionary cluster (Kilian et al., 2008).
  •  
25.
  • Francis, Matthew, 1969-, et al. (författare)
  • A study of the YopD-LcrH interaction from Yersinia pseudotuberculosis reveals a role for hydrophobic residues within the amphipathic domain of YopD
  • 2000
  • Ingår i: Molecular Microbiology. - : Blackwell Publishing. - 0950-382X .- 1365-2958. ; 38:1, s. 85-102
  • Tidskriftsartikel (refereegranskat)abstract
    • The enteropathogen Yersinia pseudotuberculosis is a model system used to study the molecular mechanisms by which Gram-negative pathogens translocate effector proteins into target eukaryotic cells by a common type III secretion machine. Of the numerous proteins produced by Y. pseudotuberculosis that act in concert to establish an infection, YopD (Yersiniaouter protein D) is a crucial component essential for yop regulation and Yop effector translocation. In this study, we describe the mechanisms by which YopD functions to control these processes. With the aid of the yeast two-hybrid system, we investigated the interaction between YopD and the cognate chaperone LcrH. We confirmed that non-secreted LcrH is necessary for YopD stabilization before secretion, presumably by forming a complex with YopD in the bacterial cytoplasm. At least in yeast, this complex depends upon the N-terminal domain and a C-terminal amphipathic α-helical domain of YopD. Introduction of amino acid substitutions within the hydrophobic side of the amphipathic α-helix abolished the YopD–LcrH interaction, indicating that hydrophobic, as opposed to electrostatic, forces of attraction are important for this process. Suppressor mutations isolated within LcrH could compensate for defects in the amphipathic domain of YopD to restore binding. Isolation of LcrH mutants unable to interact with wild-type YopD revealed no single domain responsible for YopD binding. The YopD and LcrH mutants generated in this study will be relevant tools for understanding YopD function during a Yersinia infection.
  •  
26.
  • Carlson, Karin, et al. (författare)
  • Bacteriophage T4 endonuclease II: concerted single-strand nicks yield double-strand cleavage.
  • 2004
  • Ingår i: Mol Microbiol. - : Wiley. ; 52, s. 1403-1411
  • Tidskriftsartikel (refereegranskat)abstract
    • In vivo, endonuclease II (EndoII) of coliphage T4 cleaves sites with conserved sequence elements (CSEs) to both the left and the right of the cleaved bonds, 16 bp altogether with some variability tolerated. In vitro, however, single-strand nicks in the lower strand predominate at sites containing only the left-side CSE that determines the precise position of lower strand nicks. Upper strand nick positions vary both in vivo and in vitro. A 24 bp substrate was nicked with the same precision as in longer substrates, showing that the conserved sequence suffices for precise nicking by EndoII. Using DNA ligase in vitro, we found that EndoII nicked both strands simultaneously at an in vivo-favoured site but not at an in vitro-favoured site. This indicates that the right-side CSE at in vivo-favoured sites is important for simultaneous nicking of both strands, generating double-strand cleavage. Separate analysis of the two strands following in vitro digestion at two in vitro-favoured sites showed that EndoII nicked the lower strand about 1.5-fold faster than the upper strand. In addition, the upper and lower strands were nicked independently of each other, seldom resulting in double-strand cleavage. Thus, cleavage by EndoII is the fortuitous outcome of two separate nicking events.
  •  
27.
  • Carlson, Karin, et al. (författare)
  • Endonuclease II of coliphage T4: a recombinase disguised as a restriction endonuclease?
  • 1998
  • Ingår i: Mol Microbiol. - : Wiley. ; 27:4, s. 671-676
  • Tidskriftsartikel (refereegranskat)abstract
    • EndoII shares with restriction endonucleases the property of cleaving foreign DNA while leaving the endonuclease-encoding genome intact, ensuring the survival of one DNA species in the cell. In addition, in vivo EndoII cleaves a specific DNA sequence and cleavage is context dependent. These context effects extend over at least 1000 bp, largely limiting cleavage to once within this distance. Like homing endonucleases, in vivo EndoII recognizes a long, asymmetric and degenerate consensus sequence which has two distinct parts. Recognition of one part of the consensus sequence involves base-specific bonds, and recognition of the other involves sequence-dependent helical structure. EndoII fulfils an obvious short-term survival role in ensuring the dominance of phage DNA in an infected cell, but may also have a long-term evolutionary role, producing gene-size fragments of foreign DNA to be enrolled in the phage genetic repertoire.
  •  
28.
  • Carlson, Karin, et al. (författare)
  • Sequence-specific cleavage by bacteriophage T4 endonuclease II in vitro
  • 1999
  • Ingår i: Mol Microbiol. - : Wiley. ; 31:5, s. 1395-1406
  • Tidskriftsartikel (refereegranskat)abstract
    • The 136 codon (408 bp) denA gene encoding endonuclease II (EndoII) of bacteriophage T4 was unambiguously identified through sequencing and subsequent cloning. EndoII prepared from cloned DNA through coupled in vitro transcriptiontranslation nicked and cut DNA in vitro in a sequence-specific manner. In vitro (and in vivo ), the bottom strand was nicked between the first and second base pair to the right of a top-strand CCGC motif shared by favoured in vitro and in vivo cleavage sites; top-strand cleavage positions varied. To the right of the cleavage position, favoured in vitro sites lacked a sequence element conserved at favoured in vivo sites. In pBR322 DNA, the sites cleaved in vivo as previously described were also cleaved in vitro, but in vitro additional sites were nicked or cleaved and the preference for individual sites was different. Also, different from the in vivo reaction, nicking was more frequent than ds cutting; in many copies of a ds cleavage site, only the bottom strand was nicked in vitro. A model is discussed in which sequential nicking of the two strands, and different factors influencing bottom-strand nicking and top-strand nicking, can explain the differences between the in vitro and the in vivo reaction.
  •  
29.
  • Collin, Mattias, et al. (författare)
  • Generation of a mature streptococcal cysteine proteinase is dependent on cell wall-anchored M1 protein
  • 2000
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 36:6, s. 1306-1318
  • Tidskriftsartikel (refereegranskat)abstract
    • In the present study, we have generated a mutant strain of Streptococcus pyogenes, MC25, which lacks M protein on its surface, and we demonstrate that this strain is unable to generate a mature 28 kDa cysteine proteinase. Furthermore, we show that S. pyogenes bacteria of M1 serotype are dependent on cell wall-anchored M protein to cleave the secreted zymogen into a mature cysteine proteinase. We also show that MC25 secretes a 40 kDa zymogen, having a conformation different from that secreted by wild-type bacteria. We provide data showing that the cleavage site is not blocked but, presumably, the active site is. This suggests that M protein, when anchored to the cell wall, is involved in the unfolding of the zymogen and generation of a mature cysteine proteinase that can be activated under reducing conditions. Our data add new aspects to the interaction between two important virulence factors of S. pyogenes, the streptococcal cysteine proteinase and M protein.
  •  
30.
  • Collins, James, et al. (författare)
  • Fibrinogen-binding and platelet-aggregation activities of a Lactobacillus salivarius septicaemia isolate are mediated by a novel fibrinogen-binding protein.
  • 2012
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 85:5, s. 862-877
  • Tidskriftsartikel (refereegranskat)abstract
    • The marketplace for probiotic foods is burgeoning, measured in billions of euro per annum. It is imperative, however, that all bacterial strains are fully assessed for human safety. The ability to bind fibrinogen is considered a potential pathogenicity trait that can lead to platelet aggregation, serious medical complications, and in some instances, death. Here we examined strains from species frequently used as probiotics for their ability to bind human fibrinogen. Only one strain (CCUG 47825), a Lactobacillus salivarius isolate from a case of septicaemia, was found to strongly adhere to fibrinogen. Furthermore, this strain was found to aggregate human platelets at a level comparable to the human pathogen Staphylococcus aureus. By sequencing the genome of CCUG 47825, we were able to identify candidate genes responsible for fibrinogen binding. Complementing the genetic analysis with traditional molecular microbiological techniques enabled the identification of the novel fibrinogen receptor, CCUG_2371. Although only strain CCUG 47825 bound fibrinogen under laboratory conditions, homologues of the novel fibrinogen binding gene CCUG_2371 are widespread among L. salivarius strains, maintaining their potential to bind fibrinogen if expressed. We highlight the fact that without a full genetic analysis of strains for human consumption, potential pathogenicity traits may go undetected. © 2012 Blackwell Publishing Ltd.
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31.
  • Frendeus, Björn, et al. (författare)
  • Escherichia coli P fimbriae utilize the Toll-like receptor 4 pathway for cell activation
  • 2001
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 40:1, s. 37-51
  • Tidskriftsartikel (refereegranskat)abstract
    • Fimbriae mediate bacterial attachment to host cells and provide a mechanism for tissue attack. They activate a host response by delivery of microbial products such as lipopolysaccharide (LPS) or through direct fimbriae-dependent signalling mechanisms. By coupling to glycosphingolipid (GSL) receptors, P fimbriae trigger cytokine responses in CD14 negative host cells. Here we show that P fimbriae utilize the Toll-like receptor 4 (TLR4)-dependent pathway to trigger mucosal inflammation. Escherichia coli strains expressing P fimbriae as their only virulence factor stimulated chemokine and neutrophil responses in the urinary tract of TLR4 proficient mice, but TLR4 defective mice failed to respond to infection. Mucosal cells were CD14 negative but expressed several TLR species including TLR4, and TLR4 protein was detected. Infection with P fimbriated bacteria stimulated an increase in TLR4 mRNA levels. The activation signal did not involve the LPS-CD14 pathway and was independent of lipid A myristoylation, as shown by mutational inactivation of the msbB gene. Co-staining experiments revealed that TLR4 and the GSL receptors for P fimbriae co-localized in the cell membrane. The results demonstrate that P fimbriae activate epithelial cells by means of a TLR4-dependent signalling pathway, and suggest that GSL receptors for P fimbriae can recruit TLR4 as co-receptors.
  •  
32.
  • Frick, Inga-Maria, et al. (författare)
  • Identification of a novel protein promoting the colonization and survival of Finegoldia magna, a bacterial commensal and opportunistic pathogen.
  • 2008
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 70, s. 695-708
  • Tidskriftsartikel (refereegranskat)abstract
    • Anaerobic bacteria dominate the human normal microbiota but strikingly little is known about these commensals. Finegoldia magna is a Gram-positive anaerobe found in the skin and at other non-sterile body surfaces, but it is also an opportunistic pathogen. This study describes a novel protein designated FAF (F. magnaAdhesion Factor) and expressed by more than ninety percent of F. magna isolates. The protein is present in substantial quantities at the F.magna surface but is also released from the surface. FAF forms large protein aggregates in solution and surface-associated FAF causes bacterial clumping. In skin F. magna bacteria were localized to the epidermis, where they adhere to basement membranes. FAF was found to mediate this adhesion via interactions with BM-40, a basement membrane protein. The biological significance of FAF is further underlined by the observation that it blocks the activity of LL-37, a major human antibacterial peptide. Altogether, the data demonstrate that FAF plays an important role in colonization and survival of F. magna in the human host.
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33.
  • Frick, Inga-Maria, et al. (författare)
  • Protein H--a surface protein of Streptococcus pyogenes with separate binding sites for IgG and albumin
  • 1994
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 12:1, s. 143-151
  • Tidskriftsartikel (refereegranskat)abstract
    • Protein H, a molecule expressed at the surface of some strains of Streptococcus pyogenes, has affinity for the constant (IgGFc) region of immunoglobulin (Ig) G. In absorption experiments with human plasma, protein H-sepharose could absorb not only IgG but also albumin from plasma. The affinity constant for the reaction between albumin and protein H was 7.8 x 10(9) M-1, which is higher than the affinity between IgG and protein H (Ka = 1.6 x 10(9) M-1). Fragments of protein H were generated with deletion plasmids and polymerase chain reaction (PCR) technology. Using these fragments in various protein-protein interaction assays, the binding of albumin was mapped to three repeats (C1-C3) in the C-terminal half of protein H. On the albumin molecule, the binding site for protein H was found to overlap the site for protein G, another albumin- and IgGFc-binding bacterial surface protein. Also IgGFc-binding could be mapped with the protein H fragments and the region was found N-terminally of the C repeats. A synthetic peptide (25 amino acid residues long) based on a sequence in this region was shown to inhibit the binding of protein H to immobilized IgG or IgGFc. This sequence was not found in previously described IgGFc-binding proteins. However, two other cell surface proteins of S. pyogenes exhibited highly homologous regions. The results identify IgGFc- and albumin-binding regions of protein H and further define and emphasize the convergent evolution among bacterial surface proteins interacting with human plasma proteins.
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34.
  • Fridén, H, et al. (författare)
  • Role of His residues in Bacillus subtilis cytochrome b558 for haem binding and assembly of succinate:quinone oxidoreductase (complex II)
  • 1990
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 4:6, s. 1045-1056
  • Tidskriftsartikel (refereegranskat)abstract
    • Cytochrome 5558 in the cytoplasmic membrane ofBacilius subtiiis constitutes the anchor and electronacceptor to the flavoprotein (Fp) and iron-sulphurprotein (Ip) in succinate:quinone oxidoreductase, andseemingly contains two haem groups. EPR and MCDspectroscopic data indicate bis-imidazole ligation ofthe haem. Apo-cytochrome was found in the mem-brane fraction of haem-deficient B. subtilis, suggest-ing that during biogenesis of the oxidoreductase thecytochrome b558 polypeptide is embedded into themembrane prior to the incorporation of haem andsubsequent binding of Fp and Ip. The six His residuesin cytochrome b558 were individually changed to Tyrto attempt identification of residues serving as haemaxial ligands and to analyse the role of His residues forassembly and function of the oxidoreductase. Fromthe properties of the mutants, His-47 can be excludedas a haem ligand. The remaining His residues (atpositions 13,28,70,113 and 155) are located in or closeto four predicted transmembrane segments. TheTyr-28 and Tyr-70 mutant proteins appeared to lackone of the two haems. Only the Tyr-13 and Tyr-47mutant cytochromes were found to function asanchors for Fp and Ip, but the Tyr-13 mutant cyto-chrome assembles into an enzymatically defectivesuccinate:quinone oxidoreductase. It is concludedfrom a combination of the experimental findings,sequence comparisons and membrane topology datathat His-28, His-70 and His-155 are probably haemaxial ligands in a dihaem cytochrome 6558. His-70 andHis-155 may be tigands to the same haem.
  •  
35.
  • Furukawa, Kentaro, et al. (författare)
  • Expression of the yeast aquaporin Aqy2 affects cell surface properties under the control of osmoregulatory and morphogenic signalling pathways.
  • 2009
  • Ingår i: Molecular microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 74:5, s. 1272-86
  • Tidskriftsartikel (refereegranskat)abstract
    • Aquaporins mediate rapid and selective water transport across biological membranes. The yeast Saccharomyces cerevisiae possesses two aquaporins, Aqy1 and Aqy2. Here, we show that Aqy2 is involved in controlling cell surface properties and that its expression is controlled by osmoregulatory and morphogenic signalling pathways. Deletion of AQY2 results in diminished fluffy colony morphology while overexpression of AQY2 causes strong agar invasion and adherence to plastic surfaces. Hyper-osmotic stress inhibits morphological developments including the above characteristics as well as AQY2 expression through the osmoregulatory Hog1 mitogen-activated protein kinase. Moreover, two pathways known to control morphological developments are involved in regulation of AQY2 expression: the protein kinase A pathway derepresses AQY2 expression through the Sfl1 repressor, and the filamentous growth Kss1 mitogen-activated protein kinase pathway represses AQY2 expression in a Kss1 activity-independent manner. The AQY2 expression pattern resembles in many ways that of MUC1/FLO11, which encodes a cell surface glycoprotein required for morphological developments. Our observations suggest a potential link between aquaporins and cell surface properties, and relate to the proposed role of mammalian aquaporins in tumour cell migration and invasion.
  •  
36.
  • Godaly, Gabriela, et al. (författare)
  • Role of fimbriae-mediated adherence for neutrophil migration across Escherichia coli-infected epithelial cell layers
  • 1998
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 30:4, s. 725-735
  • Tidskriftsartikel (refereegranskat)abstract
    • This study examined the role of P and type 1 fimbriae for neutrophil migration across Escherichia coli-infected uroepithelial cell layers in vitro and for neutrophil recruitment to the urinary tract in vivo. Recombinant E. coli K-12 strains differing in P or type 1 fimbrial expression were used to infect confluent epithelial layers on the underside of transwell inserts. Neutrophils were added to the upper well, and their passage across the epithelial cell layers was quantified. Infection with the P- and type 1-fimbriated recombinant E. coli strains stimulated neutrophil migration to the same extent as a fully virulent clinical E. coli isolate, but the isogenic non-fimbriated vector control strains had no stimulatory effect. The enhancement of neutrophil migration was adhesion dependent; it was inhibited by soluble receptor analogues blocking the binding of P fimbriae to the globoseries of glycosphingolipids or of type 1 fimbriae to mannosylated glycoprotein receptors. P- and type 1-fimbriated E. coli triggered higher interleukin (IL) 8 secretion and expression of functional IL-8 receptors than non-fimbriated controls, and the increase in neutrophil migration across infected cell layers was inhibited by anti-IL-8 antibodies. In a mouse infection model, P- or type 1-fimbriated E. coli stimulated higher chemokine (MIP-2) and neutrophil responses than the non-fimbriated vector controls. The results demonstrated that transformation with the pap or fim DNA sequences is sufficient to convert an E. coli K-12 strain to a host response inducer, and that fimbriation enhances neutrophil recruitment in vitro and in vivo. Epithelial chemokine production provides a molecular link between the fimbriated bacteria that adhere to epithelial cells and tissue inflammation.
  •  
37.
  • Le Brun, Nick E., et al. (författare)
  • Genes required for cytochrome c synthesis in Bacillus subtilis
  • 2000
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 36, s. 638-650
  • Tidskriftsartikel (refereegranskat)abstract
    • Cytochromes of c-type contain covalently bound haem and in bacteria are located on the periplasmic side of the cytoplasmic membrane. More than eight different gene products have been identified as being specifically required for the synthesis of cytochromes c in Gram-negative bacteria. Corresponding genes are not found in the genome sequences of Gram-positive bacteria. Using two random mutagenesis approaches, we have searched for cytochrome c biogenesis genes in the Gram-positive bacterium Bacillus subtilis. Three genes, resB, resC and ccdA, were identified. CcdA has been found previously and is required for a late step in cytochrome c synthesis and also plays a role in spore synthesis. No function has previously been assigned for ResB and ResC but these predicted membrane proteins show sequence similarity to proteins required for cytochrome c synthesis in chloroplasts. Attempts to inactivate resB and resC in B. subtilis have indicated that these genes are essential for growth. We demonstrate that various nonsense mutations in resB or resC can block synthesis of cytochromes c with no effect on other types of cytochromes and little effect on sporulation and growth. The results strongly support the recent proposal that Gram-positive bacteria, cyanobacteria, ε-proteobacteria, and chloroplasts have a similar type of machinery for cytochrome c synthesis (System II), which is very different from those of most Gram-negative bacteria (System I) and mitochondria (System III).
  •  
38.
  • Lindahl, G, et al. (författare)
  • Receptor for IgA in group A streptococci : cloning of the gene and characterization of the protein expressed in Escherichia coli
  • 1989
  • Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 3:2, s. 239-247
  • Tidskriftsartikel (refereegranskat)abstract
    • The gene for an IgA-binding protein from a group A streptococcal strain was cloned and expressed in Escherichia coli. The IgA-binding protein, called protein Arp, was purified on IgA-Sepharose, allowing complete purification in a single step. Analysis of protein Arp by Western immunoblotting demonstrated a major IgA-binding band, with an apparent molecular weight of 42 kD. The purified protein was shown to bind serum IgA and secretory IgA, as well as monoclonal IgA of both subclasses. There was no binding to IgM, IgD or IgE, but a weak binding to IgG. Inhibition experiments with whole bacteria indicated that IgA and IgG bind at separate sites. Experiments with immunoglobulin fragments showed that protein Arp binds to the Fc region of both IgA and IgG. The equilibrium constant of the reaction between protein Arp and polyclonal human IgA was determined to be 5.6 x 10(8) M-1. Amino acid sequencing of protein Arp demonstrated a direct repeat of 7 amino acids in the NH2-terminal region, a feature previously found in several streptococcal M proteins. This suggests that protein Arp, like M proteins, may be a streptococcal virulence factor.
  •  
39.
  • Macvanin, Mirjana, et al. (författare)
  • Fusidic acid-resistant EF-G perturbs the accumulation of ppGpp
  • 2000
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 37:1, s. 98-107
  • Tidskriftsartikel (refereegranskat)abstract
    • Reductions in growth rate caused by fusidic acid-resistant EF-G mutants in Salmonella typhimurium correlate strongly with increased mean cell size. This is unusual because growth rate and cell size normally correlate positively. The global transcription regulator molecule ppGpp has a role in co-ordinating growth rate and division, and its basal level normally correlates inversely with cell size at division. We show that fusidic acid-resistant EF-G mutants have perturbed ppGpp basal levels during steady-state growth and perturbed induced levels during starvation. One mutation, fusA1, associated with the slowest growth rate and largest cell size, causes a reduction in the basal level of ppGpp to one-third of that found in the wild-type strain. Other fusA mutants with intermediate or wild-type growth rates and cell sizes have either normal or increased basal levels of ppGpp. There is an inverse relationship between the basal level of ppGpp in vivo and the degree to which translation dependent on mutant EF-G is inhibited by ppGpp in vitro. This enhanced interaction between mutant EF-G and ppGpp correlates with an increased KM for GTP. Our results suggest that mutant EF-G modulates the production of ppGpp by the RelA (PSI) pathway. In conclusion, fusidic acid-resistant EF-G mutations alter the level of ppGpp and break the normal relationship between growth rate and cell size at division. It would not be surprising if other phenotypes associated with these mutants, such as loss of virulence, were also related to perturbations in ppGpp levels effected through altered transcription patterns.
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40.
  • Pagels, Martin, et al. (författare)
  • Redox sensing by a Rex-family repressor is involved in the regulation of anaerobic gene expression in Staphylococcus aureus
  • 2010
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 76:5, s. 1142-1161
  • Tidskriftsartikel (refereegranskat)abstract
    • P>An alignment of upstream regions of anaerobically induced genes in Staphylococcus aureus revealed the presence of an inverted repeat, corresponding to Rex binding sites in Streptomyces coelicolor. Gel shift experiments of selected upstream regions demonstrated that the redox-sensing regulator Rex of S. aureus binds to this inverted repeat. The binding sequence - TTGTGAAW(4)TTCACAA - is highly conserved in S. aureus. Rex binding to this sequence leads to the repression of genes located downstream. The binding activity of Rex is enhanced by NAD+ while NADH, which competes with NAD+ for Rex binding, decreases the activity of Rex. The impact of Rex on global protein synthesis and on the activity of fermentation pathways under aerobic and anaerobic conditions was analysed by using a rex-deficient strain. A direct regulatory effect of Rex on the expression of pathways that lead to anaerobic NAD+ regeneration, such as lactate, formate and ethanol formation, nitrate respiration, and ATP synthesis, is verified. Rex can be considered a central regulator of anaerobic metabolism in S. aureus. Since the activity of lactate dehydrogenase enables S. aureus to resist NO stress and thus the innate immune response, our data suggest that deactivation of Rex is a prerequisite for this phenomenon.
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41.
  • Ringdahl, Ulrika, et al. (författare)
  • A role for the fibrinogen-binding regions of streptococcal M proteins in phagocytosis resistance
  • 2000
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 37:6, s. 1318-1326
  • Tidskriftsartikel (refereegranskat)abstract
    • All virulent group A streptococcal isolates bind fibrinogen, a property that is closely linked to expression of type-specific antiphagocytic surface molecules designated M proteins. Here we show that although the M proteins from two different strains, M1 and M5, both bind fibrinogen with high affinity, they interact with different regions in the ligand. Moreover, mapping experiments demonstrated that the fibrinogen-binding regions in the M1 and M5 proteins are quite dissimilar at the amino acid sequence level and that they bind to different regions in the plasma protein. In spite of these differences, the fibrinogen-binding regions of M1 and M5 could both be shown to contribute to streptococcal survival in human blood, providing evidence for the distinct function of a plasma protein interaction in bacterial pathogenesis.
  •  
42.
  • Schmidtchen, Artur, et al. (författare)
  • Proteinases of common pathogenic bacteria degrade and inactivate the antibacterial peptide LL-37
  • 2002
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 46:1, s. 157-168
  • Tidskriftsartikel (refereegranskat)abstract
    • Effectors of the innate immune system, the anti-bacterial peptides, have pivotal roles in preventing infection at epithelial surfaces. Here we show that proteinases of the significant human pathogens Pseudomonas aeruginosa, Enterococcus faecalis, Proteus mirabilis and Streptococcus pyogenes, degrade the antibacterial peptide LL-37. Analysis by mass spectrometry of fragments generated by P. aeruginosa elastase in vitro revealed that the initial cleavages occurred at Asn-Leu and Asp-Phe, followed by two breaks at Arg-Ile, thus inactivating the peptide. Proteinases of the other pathogens also degraded LL-37 as determined by SDS-PAGE. Ex vivo, P. aeruginosa elastase induced LL-37 degradation in human wound fluid, leading to enhanced bacterial survival. The degradation was blocked by the metalloproteinase inhibitors GM6001 and 1, 10-phenantroline (both of which inhibited P. aeruginosa elastase, P. mirabilis proteinase, and E. faecalis gelatinase), or the inhibitor E64 (which inhibited S. pyogenes cysteine proteinase). Additional experiments demonstrated that dermatan sulphate and disaccharides of the structure [DeltaUA(2S)-GalNAc(4,6S)], or sucroseoctasulphate, in-hibited the degradation of LL-37. The results indicate that proteolytic degradation of LL-37 is a common virulence mechanism and that molecules which block this degradation could have therapeutic potential.
  •  
43.
  • Shannon, Oonagh, et al. (författare)
  • Severe streptococcal infection is associated with M protein-induced platelet activation and thrombus formation.
  • 2007
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 65:5, s. 1147-1157
  • Tidskriftsartikel (refereegranskat)abstract
    • Disturbed haemostasis is a central finding in severe Streptococcus pyogenes infection. In particular, microthrombi are found both at the local site of infection and at distant sites. Platelets are responsible for maintaining vascular function and haemostasis. We report here that M1 protein of S. pyogenes triggers immune-mediated platelet activation and thrombus formation. M1 protein is released from the bacterial surface and forms complexes with plasma fibrinogen. These complexes bind to the fibrinogen receptor on resting platelets. When these complexes also contain immunoglobulin G (IgG) against M1 protein, this will engage the Fc receptor on the platelets and activation will occur. Activation of the platelets leads to platelet aggregation and the generation of platelet-rich thrombi. Neutrophils and monocytes are in turn activated by the platelets. Platelet thrombi are deposited in the microvasculature, and aggregated platelets, IgG and M1 protein colocalize in biopsies from patients diagnosed with S. pyogenes toxic shock syndrome. This chain of events results in a procoagulant and pro-inflammatory state typical of severe S. pyogenes infection.
  •  
44.
  • Singh, Birendra, et al. (författare)
  • Haemophilus influenzae protein E recognizes the C-terminal domain of vitronectin and modulates the membrane attack complex.
  • 2011
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 81, s. 80-98
  • Tidskriftsartikel (refereegranskat)abstract
    • Haemophilus influenzae protein E (PE) is a 16 kDa adhesin that induces a pro-inflammatory immune response in lung epithelial cells. The active epithelial binding region comprising amino acids PE 84-108 also interferes with complement-mediated bacterial killing by capturing vitronectin (Vn) that prevents complement deposition and formation of the membrane attack complex (MAC). Here, the interaction between PE and Vn was characterized using site-directed mutagenesis. Protein E variants were produced both in soluble forms and in surface-expressed molecules on Escherichia coli. Mutations within PE(84-108) in the full-length molecule revealed that K85 and R86 residues were important for the Vn binding. Bactericidal activity against H. influenzae was higher in human serum pre-treated with full-length PE as compared with serum incubated with PE(K85E, R86D) , suggesting that PE quenched Vn. A series of truncated Vn molecules revealed that the C-terminal domain comprising Vn(353-363) harboured the major binding region for PE. Interestingly, MAC deposition was significantly higher on mutants devoid of PE due to a decreased Vn-binding capacity when compared with wild-type H. influenzae. Our results define a fine-tuned interaction between H. influenzae and the innate immune system, and identify the mode of control of the MAC that is important for pathogen complement evasion.
  •  
45.
  • Singh, Birendra, et al. (författare)
  • Vitronectin in bacterial pathogenesis: A host protein used in complement escape and cellular invasion.
  • 2010
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 78:3, s. 545-560
  • Tidskriftsartikel (refereegranskat)abstract
    • The multifunctional human glycoprotein vitronectin (Vn) plays a significant role in cell migration, tissue repair and regulation of membrane attack complex (MAC) formation. It also promotes neutrophil infiltration and, thus, enhances the inflammatory process during infection. In the host, a balanced homeostasis is maintained by Vn due to neutralization of the self-reactivity of the MAC. On the other hand, Vn bound to the bacterial surface protects from MAC mediated lysis and enhances adhesion. Gram-negative bacterial pathogens including Moraxella catarrhalis, Haemophilus influenzae, and Neisseria gonorrhoeae use Vn recruitment to prevent MAC deposition at their surface. Moreover, Gram-positive bacterial pathogens such as Streptococcus pneumoniae and S. pyogenes utilize Vn for effective adhesion to host cells and subsequent internalization. Vitronectin has an Arg-Gly-Asp (RGD) sequence for binding the host cell integrin receptors and a separate bacterial binding domain for pathogens, and thus more likely functions to cross-link bacteria and epithelial cells. Once bacteria are attached to the vitronectin-integrin complex, various host cell-signalling events are activated and promote internalization. In this review, we focus on the important roles of vitronectin in bacterial pathogenesis and describe different strategies used by pathogens to evade the host response by the help of this intriguing molecule.
  •  
46.
  • Stenberg, Lars, et al. (författare)
  • Many group A streptococcal strains express two different immunoglobulin-binding proteins, encoded by closely linked genes: characterization of the proteins expressed by four strains of different M-type
  • 1992
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 6:9, s. 1185-1194
  • Tidskriftsartikel (refereegranskat)abstract
    • Most group A streptococcal strains are able to bind immunoglobulin (Ig) in a non-immune manner, and the majority of these strains bind both IgA and IgG. Using molecular cloning and immunochemical techniques, we have purified and characterized the Ig Fc-receptors expressed by four such strains. Two of the strains express a novel type of receptor, designated protein Sir, which binds IgA and IgG of all subclasses, and therefore has broader reactivity than any Fc-receptor previously described. The other two strains express protein Arp, a receptor that binds IgA of both subclasses, and also binds polyclonal IgG weakly. Characterization of the weak IgG-binding ability of protein Arp shows that it binds only some monoclonal IgG proteins, in particular those of the IgG3 subclass. The four strains studied here were unexpectedly found to also express a second Ig-receptor, called protein Mrp, encoded by a gene closely linked to the gene for the first receptor. The Mrp protein does not bind IgA, but it binds IgG molecules of the IgG1, IgG2 and IgG4 subclasses, and it also binds fibrinogen. Binding of fibrinogen has been reported to be a characteristic property of streptococcal M proteins, which suggests that the Mrp protein may be an M protein that also binds Ig. Taken together, all available evidence now indicates that most strains of group A streptococci express two different Ig-binding proteins, encoded by closely linked genes.
  •  
47.
  • Striker, Robert, et al. (författare)
  • Structural requirements for the glycolipid receptor of human uropathogenic Escherichia coli
  • 1995
  • Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 16:5, s. 1021-1029
  • Tidskriftsartikel (refereegranskat)abstract
    • The binding of uropathogenic Escherichia coli to the globo series of glycolipids via P pili is a critical step in the infectious process that is mediated by a human‐specific PapG adhesin. Three classes of PapG adhesins exist with different binding specificities to Galα4Gal‐containing glycolipids. The structural basis for PapG recognition of the human glycolipid receptor globoside was investigated by using soluble saccharide analogues as inhibitors of bacterial haemagglutination. The minimum binding epitope was confirmed as the Galα4Gal moiety, but parts of the GalNAcβ and glucose residues, which flank the Galα4Gal in globoside (GbO4), were also shown to be important for strong binding. Furthermore, the same five hydroxyl groups of Galα4Gal in globotriasyl ceramide that were recognized by a previously characterized PapG variant were also recognized by the human‐specific PapG in binding the GbO4 that dominates In the human kidney. Saccharide analogues that blocked haemagglutination also blocked the adherence of human uropathogenic E. coli to human kidney sections. Knowledge of the molecular details of the PapG‐GbO4 interaction will make it possible to design antiadherence therapeutics.
  •  
48.
  • Svensson, Birgitta, et al. (författare)
  • Bacillus subtilis CtaA and CtaB function in haem A biosynthesis
  • 1993
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 10:1, s. 193-201
  • Tidskriftsartikel (refereegranskat)abstract
    • Haem A, a prosthetic group of many respiratory oxidases, is probably synthesized from haem B (protohaem IX) in a pathway in which haem 0 is an intermediate. Possible roles of the Bacillus subtilis ctaA and ctaB gene products in haem 0 and haem A synthesis were studied. Escherichia coli does not contain haem A. The ctaA gene on plasmids in E. coli resulted in haem A accumulation in membranes. The presence of ctaB together with ctaA increased the amount of haem A found in E. coli. Haem 0 was not detected in wild-type B. subtilis strains. A previously isolated B. subtilis ctaA deletion mutant was found to contain haem B and haem 0, but not haem A. B. subtilis ctaB deletion mutants were constructed and found to lack both haem A and haem 0. The results with E. coli and B. subtilis strongly suggest that the B. subtilis CtaA protein functions in haem A synthesis. It is tentatively suggested that it functions in the oxygenation/oxidation of the methyl side group of carbon 8 of haem 0. B. subtilis CtaB, which is homologous to Saccharomyces cerevisiae COX10 and E. coli CyoE, also has a role in haem A synthesis and seems to be required for both cytochrome a and cytochrome o synthesis.
  •  
49.
  • Svensson, Majlis, et al. (författare)
  • Glycolipid depletion in antimicrobial therapy
  • 2003
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 47:2, s. 453-461
  • Tidskriftsartikel (refereegranskat)abstract
    • Mucosal pathogens target sites of infection through specific adherence to host glycoconjugate receptors. As a consequence, depletion of such receptors from the cell surface may be expected to inhibit attachment, impair bacterial colonization and reduce the activation of mucosal inflammation. We have used the glucose analogue and glycosphingolipid (GSL) biosynthesis inhibitor N-butyldeoxynojirimycin (NB-DNJ) to deplete human uroepithelial cells and the murine urinary tract mucosa of receptors for P-fimbriated Escherichia coli. NB-DNJ blocks the ceramide-specific glucosyltransferase, which catalyses the formation of glucosyl ceramide (GlcCer), the precursor for GSLs. The inhibitor was shown to decrease the GSL content in a dose-dependent way, and depletion markedly inhibited P-fimbriated bacterial attachment in vitro. NB-DNJ-fed C3H/HeN mice were depleted of GSLs in vivo and showed reduced susceptibility to experimental urinary tract infection with P-fimbriated E. coli. The mucosal inflammatory response was impaired, as shown by reduced chemokine secretion and lower neutrophil recruitment, and the bacteria colonized the urinary tract less efficiently than in normal mice. These results confirmed the role of P fimbriae-mediated adherence for colonization and inflammation and point to an interesting alternative to antibiotic treatment for urinary tract infection.
  •  
50.
  • van der Oost, John, et al. (författare)
  • Bacillus subtilis cytochrome oxidase mutants: biochemical analysis and genetic evidence for two aa3-type oxidases
  • 1991
  • Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 5:8, s. 2063-2072
  • Tidskriftsartikel (refereegranskat)abstract
    • The ctaBCDEF genes coding for cytochrome c oxidase were found to reside adjacent to a regulatory gene ctaA at 127-degrees on the Bacillus subtilis chromosome. The structural genes for subunits I and II, ctaD and ctaC, were deleted by gene-replacement using a phleomycin-resistance marker. The mutant was unable to oxidize N,N,N',N'-tetramethyl-p-phenylenediamine and oxidized cytochrome c at a significantly lower rate. Absorption spectra of the mutant and wild-type membranes confirmed the presence of two haem A-containing enzymes in B. subtilis. Another mutant, with a spontaneous deletion upstream from ctaC, was found to express neither of these enzymes. Radioactive haem-labelling was used to identify subunit 11, which contains a haem C, and cytochrome c-550 among the membrane-bound c-type cytochromes of B. subtilis.
  •  
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