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  • 1
    Electronic Resource
    Electronic Resource
    ASSESMENT OF BACTERIAL PATHOGENESIS BY ANALYSIS OF GENE EXPRESSION IN THE HOST (2000)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Genetics 34 (2000), S. 139-164 
    Details
    ISSN: 0066-4197
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract A number of techniques have been developed to assess the expression of microbial virulence genes within the host (in vivo). These studies have shown that bacteria employ a wide variety of mechanisms to coordinately regulate the expression of these genes during infection. Two tenets have emerged from these studies: bacterial adaptation responses are critical to growth within the host, and interactions between microorganisms and the microenvironments of their hosts cannot be revealed from in vitro studies alone. Results that support these tenets include (i) the prevalent class of in vivo expressed genes are involved in adaptation to environmental stresses, (ii) pathogens recovered from host tissues (versus laboratory growth) are often more resistant to host killing mechanisms, and (iii) virulence gene expression can differ in the animal compared to laboratory media. Thus, pathogenicity comprises the unique ability to adapt to the varied host milieus encountered as the infection proceeds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.genet.34.1.139
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  • 2
    Electronic Resource
    Electronic Resource
    The essential role of the promoter-proximal subunit of CAP in pap phase variation: Lrp- and helical phase-dependent activation of papBA transcription by CAP from −215 (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: Catabolite gene activator protein (CAP) is essential for the expression of Pap pili by uropathogenic Escherichia coli. Both in vitro and in vivo analyses indicate that binding of cAMP–CAP centred at 215.5 bp upstream of the papBA promoter is essential for activation of transcription. CAP-dependent activation of papBA requires binding of the leucine-responsive regulatory protein (Lrp) at binding sites that extend from −180 to −149 relative to the start site of papBA. Our data indicate that CAP and Lrp bind independently to their respective pap DNA sites. Activation of papBA transcription was eliminated by mutations in the activating region 1 (AR1) of CAP, but not in the AR2 region, similar to class I CAP-dependent promoters. Also, like class I promoters, the C-terminal domain of the α-subunit of RNA polymerase appears to play a role in transcription activation. Moreover, phase variation is strictly dependent upon the helical phase of the CAP DNA binding site with respect to the papBA transcription start site. Using an ‘oriented heterodimer’ approach with wild-type and AR1 mutant CAPs, it was shown that the AR1 region of the CAP subunit proximal to papBA is required for stimulation of papBA transcription, whereas AR1 of the promoter-distal subunit is not. Previously, CAP was hypothesized to activate pap transcription indirectly by disrupting repression mediated by H-NS. The results presented here show that AR1 of the promoter-proximal CAP subunit was required for papBA transcription even in the absence of the histone-like protein H-NS. These results show that the promoter-proximal subunit of CAP, bound 215.5 bp upstream of the papBA transcription start site, plays an active role in stimulating papBA transcription, possibly by interacting with the C-terminal domain of the α-subunit of RNA polymerase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2001.02338.x
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  • 3
    Electronic Resource
    Electronic Resource
    Thermoregulation of Escherichia coli pap transcription: H-NS is a temperature-dependent DNA methylation blocking factor (1998)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 28 (1998), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The expression of Pap pili that facilitate the attachment of Escherichia coli to uroepithelial cells is shut off outside the host at temperatures below 26°C. Ribonuclease protection analysis showed that this thermoregulatory response was rapid as evidenced by the absence of papBA transcripts, coding for Pap pilin, after only one generation of growth at 23°C. The histone-like nucleoid structuring protein H-NS and DNA sequences within papB were required for thermoregulation, but the PapB and PapI regulatory proteins were not. In vivo analysis of pap DNA methylation patterns indicated that H-NS or a factor regulated by H-NS bound within the pap regulatory region at 23°C but not at 37°C, as evidenced by H-NS-dependent inhibition of methylation of the pap GATC sites designated GATC-I and GATC-II. These GATC sites lie upstream of the papBAp promoter and have been shown previously to play a role in controlling Pap pili expression by regulating the binding of Lrp, a global regulator that is essential for activating papBAp transcription. Competitive electrophoretic mobility shift analysis showed that H-NS bound specifically to a pap DNA fragment containing the GATC-I and GATC-II sites. Moreover, H-NS blocked methylation of these pap GATC sites in vitro : H-NS blocked pap GATC methylation at 1.4 μM but was unable to do so at higher concentrations at which non-specific binding occurred. Thus, non-specific binding of H-NS to pap DNA was not sufficient to inhibit methylation of the pap GATC sites. These results suggest that the ability of H-NS to act as a methylation blocking factor is dependent upon the formation of a specific complex of H-NS with pap regulatory DNA. We hypothesize that a function of H-NS such as oligomerization was altered at 23°C, which enabled H-NS to repress pap gene expression through the formation of a specific nucleoprotein complex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1998.00872.x
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  • 4
    Electronic Resource
    Electronic Resource
    Cells regulate their mitogenic response to thrombin through release of protease nexin (1982)
    [s.l.] : Nature Publishing Group
    Nature 298 (1982), S. 476-478 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Our previous results indicated that mouse cell-conditioned medium contains substantial amounts of protease nexin1'2. Figure 1 shows the formation of 125I-labelled thrombin-protease nexin complexes after addition of 125I-thrombin (0.14 nM) with or without unlabelled thrombin (280 nM) to mouse cells ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/298476a0
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  • 5
    Electronic Resource
    Electronic Resource
    Thrombin-mediated mitogenesis: The role of secreted protease nexin (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 112 (1982), S. 291-297 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Protease nexin (PN) is a cell-secreted protein that links to thrombin (Th) and certain other serine proteases. PN mediates the binding, internalization, and degradation of these proteases by cells (Baker et al., 1980; Low et al., 1981). Here we show that binding of Th-PN complexes to human foreskin fibroblasts (HF cells) accounted for 90% of the specific cellular Th binding at certain mitogenic doses of the protease. However, cell-associated Th-PN complexes were likely to be inactive mitogenically because heparin (170 units/ml) inhibited cellular binding of 125-Th-PN by about 95% (a reduction from 1.3 × 105 to 6 × 103 125I-Th-PN complexes per cell) but did not influence Th-mediated mitogenic stimulation. In experiments with mouse embryo cells, heparin also markedly decreased cellular binding of 125I-Th-PN without changing the mitogenic response to Th. The lack of mitogenic activity of cell-associated Th-PN complexes suggested that PN might inhibit the mitogenically essential proteolytic activity of Th. This possibility is supported by the following findings. First, amounts of serum-free conditioned culture medium that contained enough PN to complex a large fraction of added Th inhibited the clotting activity of Th. Second, heparin increased the formation of 125I-Th-PN complexes and also increased this inhibitory effect of conditioned medium. We conclude that PN acts as a negative modulator of thrombin mitogenic activity.It is shown that like other fibroblastic cells HF cells bound free 125I-Th specifically (although with relatively low affinity, Kass 〈 108 M-1). Specific binding of free 125I-Th to HF cells increased fourfold in the presence of heparin (50 IU/ml).
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041120220
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  • 6
    Electronic Resource
    Electronic Resource
    Mechanisms of thrombin-stimulated cell division (1979)
    New York, N.Y. : Wiley-Blackwell
    Journal of Supramolecular Structure 11 (1979), S. 259-267 
    Details
    ISSN: 0091-7419
    Keywords: cell surface receptors ; proteolysis of receptors ; positive or negative regulation ; Life Sciences ; Molecular Cell Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Addition of highly purified thrombin t o cultures of several kinds of nondividing fibroblasts brings about cell division. This stimulation occurs in serum-free medium, permitting studies on its mechanism under chemically defined conditions. Previous studies have shown that action of thrombin a t the cell surface is sufficient to cause cell division and that the proteolytic activity of thrombin is required for its mitogenic effect. These results prompted experiments which showed that there is a cell surface receptor for thrombin and that thrombin must hind to its receptor and cleave it to stimulate cell division. Some of the thrombin that hinds to its receptors becomes attached to them by a linkage that appears to be covalent. However, it is presently unknown whether this direct thrombin receptor complex plays a role in the stimulation.These results raise a number of question that should be explored in future studies. They also provide a foundation on which to build hypotheses about tentative molecular mechanisms that might be involved in the stimulation. Knowledge that thrombin must cleave its receptor to bring about cell division suggests two alternative mechanisms for stimulation by proteolysis. In one the receptor is a negative effector which prevents cell division when it is intact, but not after it has been cleaved. Alternatively, a fragment of the receptor could be a positive effector. In this mechanism, proteolysis by thrombin would produce a specific receptor fragment which brings about cell proliferation. If every protease which cleaves the receptor also stimulates cell division, the receptor is probably a negative effector. In contrast, if certain proteases cleave the receptor but do not stimulate the cells, a fragment of the receptor is likely a positive effector. With negative regulation by the receptor, the controlling events would occur before proteolysis of it, and it might be possible to find putative regulatory molecules by identification of nearest neighbors of the receptor. This should be possible by using bifunctional crosslinking reagents. If a fragment of the thrombin receptor turns out to be a positive effector, it should be possible to identify and study fragments by analyzing the metabolic fate of the receptor. Techniques are now available for this kind of analysis and it should also be possible to determine whether receptor fragments remain in the membrane or whether they are translocated to specific sites within the cell. A critical question to be asked is which of these events and interactions involving the thrombin receptor are necessary for stimulation of cell division. It now appears that the best way to answer this question is to examine these events in a large number of cloned cell populations that are responsive or unresponsive to the mitogenic action of thrombin. If a thrombin-mediated event occurs in all responsive clones but is altered or absent in sonie unresponsive clones, it is probably necessary for stimulation of cell division.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jss.400110215
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  • 7
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    Activation of contact-dependent antibacterial tRNase toxins by translation elongation factors (2017)
    National Academy of Sciences
    Details
    Publication Date: 2017-02-21
    Description: Contact-dependent growth inhibition (CDI) is a mechanism by which bacteria exchange toxins via direct cell-to-cell contact. CDI systems are distributed widely among Gram-negative pathogens and are thought to mediate interstrain competition. Here, we describetsfmutations that alter the coiled-coil domain of elongation factor Ts (EF-Ts) and confer resistance to the CdiA-CTEC869tRNase toxin from enterohemorrhagicEscherichia coliEC869. Although EF-Ts is required for toxicity in vivo, our results indicate that it is dispensable for tRNase activity in vitro. We find that CdiA-CTEC869binds to elongation factor Tu (EF-Tu) with high affinity and this interaction is critical for nuclease activity. Moreover, in vitro tRNase activity is GTP-dependent, suggesting that CdiA-CTEC869only cleaves tRNA in the context of translationally active GTP·EF-Tu·tRNA ternary complexes. We propose that EF-Ts promotes the formation of GTP·EF-Tu·tRNA ternary complexes, thereby accelerating substrate turnover for rapid depletion of target-cell tRNA.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 8
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    Unraveling the essential role of CysK in CDI toxin activation (2016)
    National Academy of Sciences
    Details
    Publication Date: 2016-08-16
    Description: Contact-dependent growth inhibition (CDI) is a widespread mechanism of bacterial competition. CDI+ bacteria deliver the toxic C-terminal region of contact-dependent inhibition A proteins (CdiA-CT) into neighboring target bacteria and produce CDI immunity proteins (CdiI) to protect against self-inhibition. The CdiA-CTEC536 deployed by uropathogenic Escherichia coli 536 (EC536) is a bacterial toxin 28 (Ntox28) domain that only exhibits ribonuclease activity when bound to the cysteine biosynthetic enzyme O-acetylserine sulfhydrylase A (CysK). Here, we present crystal structures of the CysK/CdiA-CTEC536 binary complex and the neutralized ternary complex of CysK/CdiA-CT/CdiIEC536. CdiA-CTEC536 inserts its C-terminal Gly-Tyr-Gly-Ile peptide tail into the active-site cleft of CysK to anchor the interaction. Remarkably, E. coli serine O-acetyltransferase uses a similar Gly-Asp-Gly-Ile motif to form the “cysteine synthase” complex with CysK. The cysteine synthase complex is found throughout bacteria, protozoa, and plants, indicating that CdiA-CTEC536 exploits a highly conserved protein–protein interaction to promote its toxicity. CysK significantly increases CdiA-CTEC536 thermostability and is required for toxin interaction with tRNA substrates. These observations suggest that CysK stabilizes the toxin fold, thereby organizing the nuclease active site for substrate recognition and catalysis. By contrast, Ntox28 domains from Gram-positive bacteria lack C-terminal Gly-Tyr-Gly-Ile motifs, suggesting that they do not interact with CysK. We show that the Ntox28 domain from Ruminococcus lactaris is significantly more thermostable than CdiA-CTEC536, and its intrinsic tRNA-binding properties support CysK-independent nuclease activity. The striking differences between related Ntox28 domains suggest that CDI toxins may be under evolutionary pressure to maintain low global stability.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 9
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    Contact-dependent growth inhibition toxins exploit multiple independent cell-entry pathways (2015)
    National Academy of Sciences
    Details
    Publication Date: 2015-08-24
    Description: Contact-dependent growth inhibition (CDI) systems function to deliver toxins into neighboring bacterial cells. CDI+ bacteria export filamentous CdiA effector proteins, which extend from the inhibitor-cell surface to interact with receptors on neighboring target bacteria. Upon binding its receptor, CdiA delivers a toxin derived from its C-terminal region. CdiA C-terminal (CdiA-CT) sequences are highly variable between bacteria, reflecting the multitude of CDI toxin activities. Here, we show that several CdiA-CT regions are composed of two domains, each with a distinct function during CDI. The C-terminal domain typically possesses toxic nuclease activity, whereas the N-terminal domain appears to control toxin transport into target bacteria. Using genetic approaches, we identified ptsG, metI, rbsC, gltK/gltJ, yciB, and ftsH mutations that confer resistance to specific CdiA-CTs. The resistance mutations all disrupt expression of inner-membrane proteins, suggesting that these proteins are exploited for toxin entry into target cells. Moreover, each mutation only protects against inhibition by a subset of CdiA-CTs that share similar N-terminal domains. We propose that, following delivery of CdiA-CTs into the periplasm, the N-terminal domains bind specific inner-membrane receptors for subsequent translocation into the cytoplasm. In accord with this model, we find that CDI nuclease domains are modular payloads that can be redirected through different import pathways when fused to heterologous N-terminal “translocation domains.” These results highlight the plasticity of CDI toxin delivery and suggest that the underlying translocation mechanisms could be harnessed to deliver other antimicrobial agents into Gram-negative bacteria.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 10
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    CdiA from Enterobacter cloacae Delivers a Toxic Ribosomal RNase into Target Bacteria (2014)
    Cell Press
    Details
    Publication Date: 2014-05-01
    Print ISSN: 0969-2126
    Electronic ISSN: 1878-4186
    Topics: Biology , Medicine
    Published by Cell Press
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