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  • 1
    Electronic Resource
    Electronic Resource
    Antibodies against synthetic peptides and the topology of LamB, an outer-membrane protein from Escherichia coli K12 (1989)
    s.l. : American Chemical Society
    Biochemistry 28 (1989), S. 8234-8241 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00446a040
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  • 2
    Electronic Resource
    Electronic Resource
    Identification of a PEST-like motif in listeriolysin O required for phagosomal escape and for virulence in Listeria monocytogenes (2001)
    Oxford, UK : Blackwell Science, Ltd
    Molecular microbiology 39 (2001), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The hly-encoded listeriolysin O (LLO) is a major virulence factor secreted by the intracellular pathogen Listeria monocytogenes, which plays a crucial role in the escape of bacteria from the phagosomal compartment. Here, we identify a putative PEST sequence close to the N-terminus of LLO and focus on the role of this motif in the biological activities of LLO. Two LLO variants were constructed: a deletion mutant protein, lacking the 19 residues comprising this sequence (residues 32–50), and a recombinant protein of wild-type size, in which all the P, E, S or T residues within this motif have been substituted. The two mutant proteins were fully haemolytic and were secreted in culture supernatants of L. monocytogenes in quantities comparable with that of the wild-type protein. Strikingly, both mutants failed to restore virulence to a hly-negative strain in vivo. In vitro assays showed that L. monocytogenes expressing the LLO deletion mutant was strongly impaired in its ability to escape from the phagosomal vacuole and, subsequently, to divide in the cytosol of infected cells. This work reveals for the first time that the N-terminal portion of LLO plays an important role in the development of the infectious process of L. monocytogenes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.2001.02281.x
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  • 3
    Electronic Resource
    Electronic Resource
    Lessons from signature-tagged mutagenesis on the infectious mechanisms of pathogenic bacteria (2005)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology reviews 29 (2005), S. 0 
    Details
    ISSN: 1574-6976
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Studies on the genetic basis of bacterial pathogenicity have been undertaken for almost 30 years, but the development of new genetic tools in the past 10 years has considerably increased the number of identified virulence factors. Signature-tagged mutagenesis (STM) is one of the most powerful general genetic approaches, initially developed by David Holden and colleagues in 1995, which has now led to the identification of hundreds of new genes requested for virulence in a broad range of bacterial pathogens. We have chosen to present in this review, the most recent and/or most significant contributions to the understanding of the molecular mechanisms of bacterial pathogenicity among over 40 STM screens published to date. We will first briefly review the principle of the method and its major technical limitations. Then, selected studies will be discussed where genes implicated in various aspects of the infectious process have been identified (including tropism for specific host and/or particular tissues, interactions with host cells, mechanisms of survival and persistence within the host, and the crossing of the blood brain barrier). The examples chosen will cover intracellular as well as extracellular Gram-negative and Gram-positive pathogens.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/j.femsre.2004.10.006
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  • 4
    Electronic Resource
    Electronic Resource
    A hypermutator phenotype attenuates the virulence of Listeria monocytogenes in a mouse model (2002)
    Oxford, UK : Blackwell Science Ltd.
    Molecular microbiology 44 (2002), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The integrity of the genetic material of bacteria is guaranteed by a set of distinct repair mechanisms. The participation of these repair systems in bacterial pathogenicity has been addressed only recently. Here, we study for the first time the participation in virulence of the MutSL mismatch repair system of Listeria monocytogenes. The mutS and mutL genes, which are contiguous in the L. monocytogenes chromosome, were identified after in silico analysis. The deduced MutS shares 62% identity with MutS of Bacillus subtilis and 50% identity with HexA, its homologue in Streptococcus pneumoniae; MutL shares 59% identity with MutL of B. subtilis and 47% identity with HexB of S. pneumoniae. Functional analysis of the mutSL locus was studied by constructing a double knock-out mutant. We showed that the deletion ΔmutSL induces: (i) a 100- to 1000-fold increase in the spontaneous mutation rate; and (ii) a 10- to 15-fold increase in the frequency of transduction, thus demonstrating the role of mutSL of L. monocytogenes in both mismatch repair and homologous recombination. We found that the deletion ΔmutSL moderately affected bacterial virulence, with a 1-log increase in the lethal dose 50% (LD50) in the mouse. Strikingly, repeated passages of the mutant strain in mice reduced virulence further. Competition assays between wild-type and mutant strains showed that the deletion ΔmutSL reduced the capacity of L. monocytogenes to survive and multiply in mice. These results thus demonstrate that, for the intracellular pathogen L. monocytogenes, a hypermutator phenotype is more deleterious than profitable to its virulence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2002.02929.x
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  • 5
    Electronic Resource
    Electronic Resource
    The svpA-srtB locus of Listeria monocytogenes: Fur-mediated iron regulation and effect on virulence (2005)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 55 (2005), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: In Listeria monocytogenes the promoter region of the svpA-srtB locus contains a well-conserved Fur box. We characterized the iron-regulation of this locus: real-time polymerase chain reaction analyses and anti-SvpA immunoblots showed that, in response to iron deprivation svpA transcription and SvpA production markedly increased (80-fold and 10-fold respectively), when initiated by either the addition of the iron chelator 2,2′-bipyridyl to BHI media, or by growth in iron-restricted minimal media. Green fluorescent protein (GFP) reporter constructs also showed increased activity of the svpA-srtB promoter in Escherichia coli (37-fold) and in L. monocytogenes (two- to threefold) when the bacteria were grown in iron-deficient conditions. A Δfur mutant of L. monocytogenes constitutively synthesized SvpA, as well as GFP fused to the svpA-srtB promoter. Cellular fractionation data revealed that in iron-rich media wild-type SvpA was exclusively secreted to the culture supernatant. However, both the Δfur derivative and wild-type L. monocytogenes grown in iron-deficient media anchored a fraction of the SvpA proteins (∼5%) to peptidoglycan, and produced a lower-molecular weight, wholly secreted form of SvpA. Together these data establish that iron availability controls transcription of the svpA-srtB locus (through Fur-mediated regulation), and attachment of SvpA to the cell wall (through SrtB-mediated covalent linkage). SvpA bears homology to IsdC, a haemin-binding protein of Staphylococcus aureus, and haemin bound to SvpA in solution. However, site-directed deletions of four structural genes and the promoter of the svpA-srtB locus did not impair haemin, haemoglobin or ferrichrome utilization in nutrition tests. We did not find strong evidence to support the notion that the svpA-srtB locus participates in haemin acquisition, as was reported for the homologous isd operon of S. aureus. Furthermore, the svpA-srtB mutant strains showed no significant attenuation of virulence in an intravenous mouse model system, but we found that the mutations reduced the persistence of L. monocytogenes in murine liver, spleen and intestines after oral administration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.2004.04436.x
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  • 6
    Electronic Resource
    Electronic Resource
    Differential roles of multiple signal peptidases in the virulence of Listeria monocytogenes (2004)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 51 (2004), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Most bacteria contain one type I signal peptidase (Spase I) for cleavage of signal peptides from exported and secreted proteins. Here, we identified a locus encoding three contiguous Spase I genes in the genome of Listeria monocytogenes. The deduced Sip proteins (denoted SipX, SipY and SipZ) are significantly similar to SipS and SipT, the major SPase I proteins of Bacillus subtilis (38% to 44% peptidic identity). We studied the role of these multiple signal peptidases in bacterial pathogenicity by constructing a series of single- and double-chromosomal knock-out mutants. Inactivation of sipX did not affect intracellular multiplication of L. monocytogenes but significantly reduced bacterial virulence (∼ 100-fold). Inactivation of sipZ impaired the secretion of phospholipase C (PC-PLC) and listeriolysin O (LLO), restricted intracellular multiplication and almost abolished virulence (LD50 of 108.3), inactivation of sipY had no detectable effects. Most importantly, a mutant expressing only SipX was impaired in intracellular survival and strongly attenuated in the mouse (LD50 of 107.2), whereas, a mutant expressing only SipZ behaved like wild-type EGD in all the assays performed. The data establish that SipX and SipZ perform distinct functions in bacterial pathogenicity and that SipZ is the major Spase I of L. monocytogenes. This work constitutes the first report on the differential role of multiple Spases I in a pathogenic bacterium and suggests a possible post-translational control mechanism of virulence factors expression.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.2004.03916.x
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  • 7
    Electronic Resource
    Electronic Resource
    Critical role of the N-terminal residues of listeriolysin O in phagosomal escape and virulence of Listeria monocytogenes (2002)
    Oxford, UK : Blackwell Science, Ltd
    Molecular microbiology 46 (2002), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A putative PEST sequence was recently identified close to the N-terminus of listeriolysin O (LLO), a major virulence factor secreted by the pathogenic Listeria monocytogenes. The deletion of this motif did not affect the secretion and haemolytic activity of LLO, but abolished bacterial virulence. Here, we first tested whether the replacement of the PEST motif of LLO by two different sequences, with either a very high or no PEST score, would affect phagosomal escape, protein stability and, ultimately, the virulence of L. monocytogenes. Then, we constructed LLO mutants with an intact PEST sequence but carrying mutations on either side, or on both sides, of the PEST motif. The properties of these mutants prompted us to construct three LLO mutants carrying single amino acid substitutions in the distal portion of the PEST region (P49A, K50A and P52A; preprotein numbering). Our data demonstrate that the susceptibility of LLO to intracellular proteolytic degradation is not related to the presence of a high PEST score sequence and that the insertion of two residues immediately downstream of the intact PEST sequence is sufficient to impair phagosomal escape and abolish bacterial virulence. Furthermore, we show that single amino acid substitutions in the distal portion of the PEST motif are sufficient to attenuate bacterial ­virulence significantly, unravelling the critical role of this region of LLO in the pathogenesis of L. ­monocytogenes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2002.03176.x
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  • 8
    Electronic Resource
    Electronic Resource
    In vivo and in vitro studies of major surface loop deletion mutants of the Escherichia coli K-12 maltoporin: contribution to maltose and maltooligosaccharide transport and binding (1999)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 32 (1999), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The trimeric protein LamB of Escherichia coli K-12 (maltoporin) specifically facilitates the diffusion of maltose and maltooligosaccharides through the outer membrane. Each monomer consists of an 18-stranded antiparallel β-barrel with nine surface loops (L1 to L9). The effects on transport and binding of the deletion of some of the surface loops or of combinations of several of them were studied in vivo and in vitro. In vivo, single-, ΔL4, ΔL5, ΔL6, and double-loop deletions, ΔL4 + ΔL5 and ΔL5 + ΔL6, abolished maltoporin functions, but not the double deletion ΔL4 + ΔL6 and the triple deletion ΔL4 + ΔL5 + ΔL6. While deletion of the central variable portion of loop L9 (ΔL9v) affected maltoporin function only moderately, the combination of ΔL9v with the double deletion of loops L4 and L6 (triple deletion ΔL4 + ΔL6 + ΔL9v) strongly impaired maltoporin function and resulted in sensitivity to large hydrophilic antibiotics without change in channel size as measured in vitro. In vitro, the carbohydrate-binding properties of the different loop mutants were studied in titration experiments using the asymmetric and symmetric addition of the mutant porins and of the carbohydrates to one or both sides of the lipid bilayer membranes. The deletion of loop L9v alone (LamBΔL9v), of two loops L4 and L6 (LamBΔL4 +ΔL6), of three loops L4, L5 and L6 (LamBΔL4 +ΔL5 + ΔL6) or of L4, L6 and L9v (LamBΔL4 + ΔL6 +ΔL9v) had relatively little influence on the carbohydrate-binding properties of the mutant channels, and they had approximately similar binding properties for carbohydrate addition to both sides compared with only one side. The deletion of one of the loops L4 (LamBΔL4) or L6 (LamBΔL6) resulted in an asymmetric carbohydrate binding. The in vivo and in vitro results, together with those of the purification across the starch column, suggest that maltooligosaccharides enter the LamB channel from the cell surface side with the non-reducing end in advance. The absence of some of the loops leads to obstruction of the channel from the outside, which results in a considerable difference in the on-rate of carbohydrate binding from the extracellular side compared with that from the periplasmic side.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1999.01406.x
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  • 9
    Electronic Resource
    Electronic Resource
    In vivo and in vitro studies of transmembrane β-strand deletion, insertion or substitution mutants of the Escherichia coli K-12 maltoporin (2000)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 35 (2000), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: LamB of Escherichia coli K12, also called maltoporin, is an outer membrane protein, which specifically facilitates the diffusion of maltose and maltodextrin through the bacterial outer membrane. Each monomer is composed of an 18-stranded antiparallel β-barrel. In the present work, on the basis of the known X-ray structure of LamB, the effects of modifications of the β-barrel domain of maltoporin were studied in vivo and in vitro. We show that: (i) the substitution of the pair of strands β13–β14 of the E. coli maltoporin with the corresponding pair of strands from the functionally related maltoporin of Salmonella typhimurium yielded a protein active in vivo and in vitro; and (ii) the removal of one pair of β-strands (deletion β13–β14) from the E. coli maltoporin, or its replacement by a pair of strands from the general porin OmpF of E. coli, leads to recombinant proteins that lost in vivo maltoporin activities but still kept channel formation and carbohydrate binding in vitro. We also inserted into deletion β13–β14 the portion of the E. coli LamB protein comprising strands β13 to β16. This resulted in a protein expected to have 20 β-strands and which completely lost all LamB-specific activities in vivo and in vitro.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2000.01748.x
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  • 10
    Electronic Resource
    Electronic Resource
    Expression of Human β1 and β2 Adrenergic Receptors in E. Coli As a New Tool for Ligand Screening (1989)
    [s.l.] : Nature Publishing Company
    Nature biotechnology 7 (1989), S. 923-927 
    Details
    ISSN: 1546-1696
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: [Auszug] E. coli transformed with appropriate plasmid vectors express human β1 and β2-adrenergic receptors that retain the binding properties of the corresponding receptors in mammalian tissues. The experimental procedure required for pharmacological studies on active receptors expressed in ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nbt0989-923
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