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  • 11
    Electronic Resource
    Electronic Resource
    A tyrosine-phosphorylated 12-amino-acid sequence of enteropathogenic Escherichia coli Tir binds the host adaptor protein Nck and is required for Nck localization to actin pedestals (2002)
    Oxford, UK : Blackwell Science Ltd.
    Molecular microbiology 43 (2002), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Enteropathogenic Escherichia coli (EPEC) and enterohaemorrhagic E. coli (EHEC) each promote the reorganization of actin into filamentous pedestal structures beneath attached bacteria during colonization of the intestinal epithelium. Central to this process is the translocation of the protein Tir (translocated intimin receptor) into the plasma membrane of host cells, where it interacts with the bacterial outer membrane protein intimin and triggers cellular signalling events that lead to actin rearrangement. Actin signalling by EPEC Tir requires a tyrosine residue, Y474, which is phosphorylated in the host cell. In contrast, EHEC Tir lacks this residue and generates pedestals independently of tyrosine phosphorylation. Consistent with this difference, recent work indicates that EHEC Tir cannot functionally replace EPEC Tir. To identify the role that tyrosine phosphorylation of EPEC Tir plays in actin signalling, we generated chimeric EHEC/EPEC Tir proteins and identified a 12-residue sequence of EPEC Tir containing Y474 that confers actin-signalling capabilities to EHEC Tir when the chimera is expressed in EPEC. Nck, a mammalian adaptor protein that has been implicated in the initiation of actin signalling, binds to this sequence in a Y474 phosphorylation-dependent manner and is recruited to the pedestals of EPEC, but not of EHEC.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2002.02817.x
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  • 12
    Electronic Resource
    Electronic Resource
    Identification of a candidate glycosaminoglycan-binding adhesin of the Lyme disease spirochete Borrelia burgdorferi (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: Binding of glycosaminoglycans (GAGs) by Borrelia burgdorferi, the Lyme disease spirochete, has the potential to promote the colonization of diverse tissues. GAG binding by B. burgdorferi is associated with haemagglutination and we have identified a 26 kDa protein, which we have termed Bgp (BorreliaGAG-binding protein), on the basis of its ability to bind to heparin and erythrocytes. Bgp was found in outer membrane fractions of B. burgdorferi and on the surface of intact bacteria, as assayed by labelling with a membrane-impermeable biotinylating agent or anti-Bgp antibodies. Purified recombinant Bgp agglutinated erythrocytes, binds to the same spectrum of GAGs as the B. burgdorferi strain from which the cloned bgp sequence was obtained, and inhibited B. burgdorferi binding to purified GAGs and to cultured mammalian cells. Thus, Bgp is a strong candidate for a GAG-binding adhesin of B. burgdorferi.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2000.01792.x
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  • 13
    Electronic Resource
    Electronic Resource
    Platelet activation by a relapsing fever spirochaete results in enhanced bacterium–platelet interaction via integrin αIIbβ3 activation (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: Borrelia hermsii, a spirochaete responsible for relapsing fever in humans, grows to high density in the bloodstream and causes thrombocytopenia. We show here that B. hermsii binds to human platelets. Extended culture in bacteriological medium resulted in both diminished infectivity in vivo and diminished platelet binding in vitro. Platelet binding was promoted by the platelet integrin αIIbβ3: the bacterium bound to purified integrin αIIbβ3, and bacterial binding to platelets was diminished by αIIbβ3 antagonists or by a genetic defect in this integrin. Integrin αIIbβ3 undergoes a conformational change upon platelet activation, and bacteria bound more efficiently to activated rather than resting platelets. Nevertheless, B. hermsii bound at detectable levels to preparations of resting platelets. The bacterium did not recognize a point mutant of αIIbβ3 that cannot acquire an active conformation. Rather, B. hermsii was capable of triggering platelet and integrin αIIbβ3 activation, as indicated by the expression of the platelet activation marker P-selectin and integrin αIIbβ3 in its active conformation. The degree of platelet activation varied depending upon bacterial strain and growth conditions. Prostacyclin I2, an inhibitor of platelet activation, diminished bacterial attachment, indicating that activation enhanced bacterial binding. Thus, B. hermsii signals the host cell to activate a critical receptor for the bacterium, thereby promoting high-level bacterial attachment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2001.02201.x
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  • 14
    Electronic Resource
    Electronic Resource
    The Tir-binding region of enterohaemorrhagic Escherichia coli intimin is sufficient to trigger actin condensation after bacterial-induced host cell signalling (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: Enterohaemorrhagic Escherichia coli (EHEC) has emerged as an important agent of diarrhoeal disease. Attachment to host cells, an essential step during intestinal colonization by EHEC, is associated with the formation of a highly organized cytoskeletal structure containing filamentous actin, termed an attaching and effacing (A/E) lesion, directly beneath bound bacteria. The outer membrane protein intimin is required for the formation of this structure, as is Tir, a bacterial protein that is translocated into the host cell and is thought to function as a receptor for intimin. To understand intimin function better, we fused EHEC intimin to a homologous protein, Yersinia pseudotuberculosis invasin, or to maltose-binding protein. The N-terminal 539 amino acids of intimin were sufficient to promote outer membrane localization of the C-terminus of invasin and, conversely, the N-terminal 489 amino acids of invasin were sufficient to promote the localization of the C-terminus of intimin. The C-terminal 181 residues of intimin were sufficient to bind mammalian cells that had been preinfected with an enteropathogenic E. coli strain that expresses Tir but not intimin. Binding of intimin derivatives to preinfected cells correlated with binding to recombinant Tir protein. Finally, the 181-residue minimal Tir-binding region of intimin, when purified and immobilized on latex beads, was sufficient to trigger A/E lesions on preinfected mammalian cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1999.01574.x
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  • 15
    Electronic Resource
    Electronic Resource
    Variable small protein (Vsp)-dependent and Vsp-independent pathways for glycosaminoglycan recognition by relapsing fever spirochaetes (2000)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 36 (2000), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Tick-borne relapsing fever, caused by pathogenic Borrelia such as B. hermsii and B. turicatae, features recurrent episodes of bacteraemia, each of which is caused by a population of spirochaetes that expresses a different variable major protein. Relapsing fever is also associated with the infection of a variety of tissues, such as the central nervous system. In this study, we show that glycosaminoglycans (GAGs) mediate the attachment of relapsing fever spirochaetes to mammalian cells. B. hermsii strain DAH bound to immobilized heparin, and heparin and dermatan sulphate blocked bacterial binding to host cells. Bacterial binding was diminished by inhibition of host cell GAG synthesis or sulphation, or by the enzymatic removal of GAGs. GAGs mediated the attachment of relapsing fever spirochaetes to potentially relevant target cells, such as endothelial and glial cells. B. hermsii was able to attach to GAGs independently of variable major proteins, because strains expressing the variable major proteins Vsp33, Vlp7 or no variable major protein at all each recognized GAGs. Nevertheless, we found that a variable major protein of B. turicatae directly promoted GAG binding by this relapsing fever spirochaete. B. turicatae strain Oz1 serotype B, which expresses the variable major protein VspB, bound to GAGs more efficiently than did B. turicatae Oz1 serotype A, which expresses VspA. Recombinant VspB, but not VspA, bound to heparin and dermatan sulphate. Previous studies have shown that strain Oz1 serotype B grows to higher concentrations in the blood than does Oz1 serotype A. Thus, relapsing fever spirochaetes have the potential to express Vsp-dependent and Vsp-independent GAG-binding activities and, for one pair of highly related B. turicatae strains, differences in GAG binding correlate with differences in tissue tropism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2000.01906.x
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  • 16
    Electronic Resource
    Electronic Resource
    Identification and characterization of the pupB gene encoding an inducible ferric-pseudobactin receptor of Pseudomonas putida WCS358 (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: Pseudomonas putida WCS358 can transport iron complexed to a wide variety of pseudobactins produced by other Pseudomonas strains. The pupB gene encoding an outer membrane ferric-pseudobactin receptor was isolated from a genomic library of P. putida WCS358. The PupB receptor facilitated iron transport via two distinct heterologous siderophores, i.e. pseudobactin BN8 and pseudobactin BN7. The amino acid sequence deduced from the nucleotide sequence consisted of 804 amino acids (molecular weight 88369) of which the N-terminal part was very similar to a prokaryotic leader peptide. The mature protein shared significant homology with the receptor for ferric-pseudobactin 358 (PupA) and contained three regions common to TonB-dependent receptor proteins of Eschenchia coli. Interestingly, PupB expression was only observed in cells cultured in iron-deficient medium containing pseudobactin BN8 or pseudobactin BN7. This expression required a transcriptional unit, pupR, identified upstream of the structurai pupB gene. Transposon Tn5 insertion mutants defective in PupB production still exhibited uptake of iron via pseudobactin BN8, although with reduced efficiency. Apparently, an additional transport system for this ferric-siderophore complex operates in this strain. In addition to pseudobactin BN8 also other heterologous siderophores were capable of inducing synthesis of specific high-molecular-weight outer membrane proteins in strain WCS358, which suggests the existence of multiple siderophore-inducible iron transport systems in this strain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb01603.x
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  • 17
    Electronic Resource
    Electronic Resource
    Characterization of a candidate Borrelia burgdorferiβ3-chain integrin ligand identified using a phage display library (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 spirochaetal agents of Lyme disease, Borrelia burgdorferi (sensu lato) bind to integrins αIIbβ3, αvβ3 and α5β1 in purified form and on the surfaces of human cells. Using a phage display library of B. burgdorferi (sensu stricto) DNA, a candidate ligand for β3-chain integrins was identified. The native B. burgdorferi protein, termed p66, is known to be recognized by human Lyme disease patient sera and to be expressed on the surface of the spirochaete. We show here that recombinant p66 binds specifically to β3-chain integrins and inhibits attachment of intact B. burgdorferi to the same integrins. When expressed on the surface of Escherichia coli, this protein increases the attachment of E. coli to a transfected cell line that expresses αvβ3, but not to the parental cell line, which expresses no β3-chain integrins. Localization of p66 on the surface of B. burgdorferi, the ability of recombinant forms of the protein to bind to β3-chain integrins and the fact that p66 and B. burgdorferi bind to β3-chain integrins in a mutually exclusive manner make p66 an attractive candidate bacterial ligand for integrins αIIbβ3 and αvβ3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1999.01654.x
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  • 18
    Electronic Resource
    Electronic Resource
    Identification and characterization of a siderophore regulatory gene (pfrA) of Pseudomonas putida WCS358: homology to the alginate regulatory gene aigQ of Pseudomonas aeruginosa (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 10 (1993), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Genes encoding biosynthesis of pseudobactin 358 (a microbial iron transport agent) and its cognate outer membrane receptor protein. PupA, are transcribed only under iron limitation in plant growth-promoting Pseudomonas putida WCS358. Two cosmid clones were identified from a gene bank of WCS358 DNA which could independently and in an iron-dependent manner activate transcription from a WCS358 siderophore gene promoter in heterologous Pseudomonas strain A225. The functional region of one of the clones was localized by subcloning, transposon Tn3Gus mutagenesis, and DNA sequencing. Genomic transposon insertion mutants in the functional region lost the capacity to activate a siderophore gene promoter fusion transcriptionally; furthermore, these mutants no longer produced pseudobactin 358. The activating region consisted of a single gene designated pfrA (Pseudomonasferric regulator). The pfrA gene codes for a single polypeptide, PfrA, of approximately 18kDa, which has 58% identity to AlgQ (also known as AlgR2), a positive regulator involved in transcriptionally regulating alginate biosynthesis in Pseudomonas aeruginosa. Cross-complementation studies between the pfrA gene of P. putida and the algQ gene of P. aeruginosa revealed that pfrA can restore mucoidy (alginate production) in an algQ mutant and that algQ could poorly complement a pfrA genomic mutant. It is concluded that PfrA is involved in the positive regulation of siderophore biosynthetic genes in response to iron limitation; furthermore, pfrA and algQ appeared to be interchangeable between P. putida and P. aeruginosa.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb00904.x
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  • 19
    Electronic Resource
    Electronic Resource
    Solving a sticky problem: new genetic approaches to host cell adhesion by the Lyme disease spirochete (2005)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 57 (2005), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The Lyme disease spirochetes, comprised of at least three closely related species, Borrelia burgdorferi, Borrelia garinii and Borrelia afzelii, are fascinating and enigmatic bacterial pathogens. They are maintained by tick-mediated transmission between mammalian hosts, usually small rodents. The ability of these bacteria, which have relatively small genomes, to survive and disseminate in both an immunocompetent mammal and in an arthropod vector suggests that they have evolved elegant and indispensable strategies for interacting with their hosts. Recognition of specific mammalian and tick tissues is likely to be essential for successful completion of the enzootic life cycle but, given the historical difficulties in genetic manipulation of these organisms, characterization of factors promoting cell adhesion has until recently largely been confined to either the manipulation of host cells or the analysis of potential bacterial ligands in the form of recombinant proteins. These studies have led to the identification of several mammalian receptors for Lyme disease spirochetes, including glycosaminoglycans, decorin, fibronectin and integrins, as well as a tick receptor for the bacterium, and also candidate cognate bacterial ligands. Recent advances in our ability to genetically manipulate Lyme disease spirochetes, particularly B. burgdorferi, are now providing us with firm evidence that these ligands indeed do promote bacterial adherence to host cells, and with new insights into the roles of these multifacted Borrelia–host cell interactions during mammalian and arthropod infection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.2005.04759.x
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  • 20
    Electronic Resource
    Electronic Resource
    Self-association of EPEC intimin mediated by the β-barrel-containing anchor domain: a role in clustering of the Tir receptor (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: Outer membrane intimin directs attachment of enteropathogenic Escherichia coli (EPEC) via its Tir receptor in mammalian target cell membranes. Phosphorylation of Tir triggers local actin polymerization and the formation of ‘pedestal-like’ pseudopods. We demonstrate that the intimin protein contains three domains, a flexible N-terminus (residues 40–188), a central membrane-integrated β-barrel (189–549), and a tightly folded Tir-binding domain (550–939). Intimin was shown by electron microscopy to form ring-like structures with a ∼7 nm external diameter and an electron dense core, and to form channels of 50picoSiemens conductance in planar lipid bilayers. Gel filtration, multiangle light scattering and cross-linking showed that this central β-barrel membrane-anchoring domain directs intimin dimerization. Isothermal titration calorimetry revealed a high affinity, single-binding site interaction of 2 : 1 stoichiometry between dimeric intimin and Tir, and modelling suggests that this interaction determines a reticular array-like superstructure underlying receptor clustering. In support of this model, actin rearrangement induced in Tir-primed cultured cells by intimin-containing proteoliposomes was dependent on the concentration of both intimin and Tir, and co-localized with clustered phosphorylated Tir.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2003.03830.x
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