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  • 1
    Electronic Resource
    Electronic Resource
    The HlyB/HlyD-dependent secretion of toxins by Gran-negative bacteria (1992)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 105 (1992), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Hemolysin (HlyA) and related toxins are secreted across both the cytoplasmic and outer membranes of Escherichia coli and other pathogenic Gram-negative bacteria in a remarkable process which proceeds without a periplasmic intermediate. It is directed by an uncleaved C-terminal targetting signal and the HlyD and HlyB translocator proteins, the latter of which are members of a transporter superfamily central to import and export of a wide range of substrates by prokaryotic and eukaryotic cells. Our mutational analyses of the HlyA targetting signal and definition for the first time of stages and intermediates in the HlyB/HlyD-dependent translocation allow a discussion of the hemolysin export process in the wider context of protein translocation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1992.tb05885.x
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  • 2
    Electronic Resource
    Electronic Resource
    Activation of Escherichia coli prohemolysin to the membrane-targetted toxin by HlyC-directed ACP-dependent fatty acylation (1992)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 105 (1992), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Hemolysin (HlyA) and related toxins of Escherichia coli and other Gram-negative pathogenic bacteria form membrane pores in cells of the host immune system, causing cell dysfunction and death. An insight into the mechanism by which HlyA is targetted to mammalian cell membranes was achieved by establishing in vitro activation of the non-toxic precursor proHlyA. By this approach we have discovered that conversion of proHlyA to the post-translational active HlyA toxin is determined by fatty acylation of proHlyA in an apparently novel process directed by the HlyC homodimer activator protein, and dependent upon the cellular acyl carrier protein (ACP). By further exploiting the in vitro activation system it is now possible to obtain direct evidence that HlyC binds to an internal recognition sequence in the proHlyA precursor, in this way providing specificity for the transfer to proHlyA of a fatty acid moiety carried by the ACP. It is possible that the fatty acid modification determines directly the binding of HlyA to mammalian membrane lipids, thus initiating the toxin interaction with the target cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1992.tb05884.x
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  • 3
    Electronic Resource
    Electronic Resource
    STRUCTURE AND FUNCTION OF TOLC: The Bacterial Exit Duct for Proteins and Drugs (2004)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Biochemistry 73 (2004), S. 467-489 
    Details
    ISSN: 0066-4154
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Biology
    Notes: The bacterial TolC protein plays a common role in the expulsion of diverse molecules, which include protein toxins and antibacterial drugs, from the cell. TolC is a trimeric 12-stranded alpha/beta barrel, comprising an alpha-helical trans-periplasmic tunnel embedded in the outer membrane by a contiguous beta-barrel channel. This structure establishes a 140 A long single pore fundamentally different to other membrane proteins and presents an exit duct to substrates, large and small, engaged at specific inner membrane translocases. TolC is open to the outside medium but is closed at its periplasmic entrance. When TolC is recruited by a substrate-laden translocase, the entrance is opened to allow substrate passage through a contiguous machinery spanning the entire cell envelope, from the cytosol to the external environment. Transition to the transient open state is achieved by an iris-like mechanism in which entrance alpha-helices undergo an untwisting realignment, thought to be stabilized by interaction with periplasmic helices of the translocase. TolC family proteins are ubiquitous among gram-negative bacteria, and the conserved entrance aperture presents a possible cheomotherapeutic target in multidrug-resistant pathogens.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.biochem.73.011303.074104
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  • 4
    Electronic Resource
    Electronic Resource
    STRUCTURE AND FUNCTION OF TOLC: The Bacterial Exit Duct for Proteins and Drugs (2004)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Biochemistry 73 (2004), S. 467-489 
    Details
    ISSN: 0066-4154
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Biology
    Notes: The bacterial TolC protein plays a common role in the expulsion of diverse molecules, which include protein toxins and antibacterial drugs, from the cell. TolC is a trimeric 12-stranded alpha/beta barrel, comprising an alpha-helical trans-periplasmic tunnel embedded in the outer membrane by a contiguous beta-barrel channel. This structure establishes a 140 A long single pore fundamentally different to other membrane proteins and presents an exit duct to substrates, large and small, engaged at specific inner membrane translocases. TolC is open to the outside medium but is closed at its periplasmic entrance. When TolC is recruited by a substrate-laden translocase, the entrance is opened to allow substrate passage through a contiguous machinery spanning the entire cell envelope, from the cytosol to the external environment. Transition to the transient open state is achieved by an iris-like mechanism in which entrance alpha-helices undergo an untwisting realignment, thought to be stabilized by interaction with periplasmic helices of the translocase. TolC family proteins are ubiquitous among gram-negative bacteria, and the conserved entrance aperture presents a possible cheomotherapeutic target in multidrug-resistant pathogens.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.biochem.73.011303.074104
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  • 5
    Electronic Resource
    Electronic Resource
    Increased distal gene transcription by the elongation factor RfaH, a specialized homologue of NusG (1996)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 22 (1996), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The Escherichia coli RfaH protein is required for the expression of operons directing synthesis and export of the toxin haemolysin, the lipopolysaccharide core, and the F-factor sex pilus. Mutation of rfaH increases transcriptional polarity along all three operons. By demonstrating strong RfaH-dependent suppression of transcription polarity in vitro, we have established RfaH as a novel transcriptional activator, and we reveal that RfaH is a homologue of the essential protein NusG that modulates general transcriptional pausing and termination in prokaryotes. Full transcription of the distal genes from an upstream promoter required RfaH and the 5′ cis-acting ops element, both in vivo and in vitro. In vivo the requirement for the ops element was suppressed by overexpressing RfaH, and in vitro the presence of ops lowered the concentration of RfaH required to stimulate transcript elongation. We suggest that RfaH directs transcript elongation in an analogous way to NusG, but does so in a subset of bacterial operons primarily engaged in the production of extracellular components required for virulence and fertility.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1996.d01-1726.x
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  • 6
    Electronic Resource
    Electronic Resource
    Suppression of transcription polarity in the Escherichia coli haemolysin operon by a short upstream element shared by polysaccharide and DNA transfer determinants (1996)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 19 (1996), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Expression of the Escherichia coli hlyCABD operon encoding synthesis, maturation and export of haemolysin toxin was strongly dependent upon a 35 bp DNA sequence, spanning the element GGCGGTAG, located 2 kbp upstream. When the hly operon was placed under the control of the inducible tac promoter, expression remained dependent upon this element, when transcribed in its native orientation 3′ of the promoter. The increase in ptac-directed transcription was strongest for the distal, export genes of the hly operon, and was particularly striking when ptac and the element were placed far upstream. The element did not influence transcript stability, and we suggest that it is a key component of a novel regulatory mechanism may suppresses transcription polarity within operons. The mechanism that be of widespread importance in bacterial gene expression because the 8 bp element is present in many Gram-negative species as an upstream component of operons encoding the production of toxins and the surface assembly of polysaccharides and components required for the conjugal transfer of DNA. We name it the ops element for operon polarity suppressor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1996.446951.x
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  • 7
    Electronic Resource
    Electronic Resource
    Membrane fusion activity of purified SipB, a Salmonella surface protein essential for mammalian cell invasion (2000)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 37 (2000), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: An early event in Salmonella infection is the invasion of non-phagocytic intestinal epithelial cells. The pathogen is taken up by macropinocytosis, induced by contact-dependent delivery of bacterial proteins that subvert signalling pathways and promote cytoskeletal rearrangement. SipB, a Salmonella protein required for delivery and invasion, was shown to localize to the cell surface of bacteria invading mammalian target cells and to fractionate with outer membrane proteins. To investigate the properties of SipB, we purified the native full-length protein following expression in recombinant Escherichia coli. Purified SipB assembled into hexamers via an N-terminal protease-resistant domain predicted to form a trimeric coiled coil, reminiscent of viral envelope proteins that direct homotypic membrane fusion. The SipB protein integrated into both mammalian cell membranes and phospholipid vesicles without disturbing bilayer integrity, and it induced liposomal fusion that was optimal at neutral pH and influenced by membrane lipid composition. SipB directed heterotypic fusion, allowing delivery of contents from E. coli-derived liposomes into the cytosol of living mammalian cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2000.02027.x
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  • 8
    Electronic Resource
    Electronic Resource
    An ordered reaction mechanism for bacterial toxin acylation by the specialized acyltransferase HlyC: formation of a ternary complex with acylACP and protoxin substrates (1999)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 34 (1999), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The 110 kDa haemolysin protoxin (proHlyA) is activated in the Escherichia coli cytosol by acyl carrier protein-dependent fatty acylation of two internal lysine residues, directed by the co-synthesized protein HlyC. Using an in vitro maturation reaction containing purified protoxin peptides and acylACP, we show unambiguously that HlyC possesses an apparently unique acyltransferase activity fully described by Michaelis–Menten analysis. The Vmax of HlyC at saturating levels of both substrates was ≈ 115 nmol acyl group min−1 mg−1 with KmacylACP of 260 nM and KmproHlyA of 27 nM, kinetic parameters sufficient to explain why in vivo HlyC is required at a concentration equimolar to proHlyA. HlyC bound the fatty acyl group from acylACP to generate an acylated HlyC intermediate that was depleted in the presence of proHlyA, but enriched in the presence of proHlyA derivatives lacking acylation target sites. HlyC was also able to bind in vivo 4′-phosphopantetheine. Substitution of conserved amino acids that could act as putative covalent attachment sites did not prevent binding of the fatty acyl or 4′-phosphopantetheine groups. These data and substrate variation analyses suggest that the unique acylation reaction does not involve covalent attachment of fatty acid to the acyltransferase, but rather that it proceeds via a sequential ordered Bi–Bi reaction mechanism, requiring the formation of a non-covalent ternary acylACP–HlyC–proHlyA complex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1999.01648.x
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  • 9
    Electronic Resource
    Electronic Resource
    ATPase activity and ATP/ADP-induced conformational change in the soluble domain of the bacterial protein translocator HlyB (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 8 (1993), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The haemolysin exporter HlyB and its homologues are central to the unconventional signal-peptide-independent secretion of toxins, proteases and nodulation proteins by bacteria. HlyB is a member of the ATP-binding cassette (ABC) or traffic ATPase superfamily, and resembles closely in structure and function mammalian exporters such as the multidrug-resistance P-glycoprotein, combining both integral membrane and cytosolic domains. Overproduction of the HlyB cytopiasmic domain as a C -terminal peptide fused to glutathione S-transferase allowed the direct affinity purification and concentration of 30-50 mg ml−1 of soluble protein (GST-Bctp) in an apparently dimeric form possessing both transferase and ATPase activity. GST-Bctp bound to ADP-agarose and was eluted specifically by ATP and ADP, affinity behaviour which was confirmed in both the full-length HlyB and the unfused HlyB cytoplasmic domain synthesized in vitro. The stoichiometry of binding to MgATP and MgADP was close to equimolar and both ligands induced substantial conformational change in the protein. Mg2+ -dependent ATPase activity of GST-Bctp Vmax 17mu;mol min−1 mg−1, Km 0.2 mM) was comparable with the activity of the bacterial importer MalK and human P-glycoprotein reconstituted into proteoliposomes, and over an order of magnitude higher than in vitro measurements of disaggregated MalK purified from inclusion bodies. Activity was unaffected by inhibitors of F- and V-type ATPases, non-hydrolysable ATP analogues, or translocation substrate, but was severely inhibited by inhibitors of E1E2 (P-type) ATPases, and the acidic phospholipid phosphatidyl glycerol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb01661.x
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  • 10
    Electronic Resource
    Electronic Resource
    The target cell plasma membrane is a critical interface for Salmonella cell entry effector–host interplay (2004)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 54 (2004), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Salmonella species trigger host membrane ruffling to force their internalization into non-phagocytic intestinal epithelial cells. This requires bacterial effector protein delivery into the target cell via a type III secretion system. Six translocated effectors manipulate cellular actin dynamics, but how their direct and indirect activities are spatially and temporally co-ordinated to promote productive cytoskeletal rearrangements remains essentially unexplored. To gain further insight into this process, we applied mechanical cell fractionation and immunofluorescence microscopy to systematically investigate the subcellular localization of epitope-tagged effectors in transiently transfected and Salmonella-infected cultured cells. Although five effectors contain no apparent membrane-targeting domains, all six localized exclusively in the target cell plasma membrane fraction and correspondingly were visualized at the cell periphery, from where they induced distinct effects on the actin cytoskeleton. Unexpectedly, no translocated effector pool was detectable in the cell cytosol. Using parallel in vitro assays, we demonstrate that the prenylated cellular GTPase Cdc42 is necessary and sufficient for membrane association of the Salmonella GTP exchange factor and GTPase-activating protein mimics SopE and SptP, which have no intrinsic lipid affinity. The data show that the host plasma membrane is a critical interface for effector–target interaction, and establish versatile systems to further dissect effector interplay.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.2004.04336.x
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