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Release of the type I secreted α-haemolysin via outer membrane vesicles from Escherichia coli
Umeå universitet, Medicinska fakulteten, Institutionen för molekylärbiologi (Medicinska fakulteten).
Umeå universitet, Medicinska fakulteten, Institutionen för molekylärbiologi (Medicinska fakulteten).
Umeå universitet, Medicinska fakulteten, Institutionen för molekylärbiologi (Medicinska fakulteten). (Bernt Eric Uhlin)
Department of Bacteriology, Faculty of Medical Sciences, Kyushu University, Fukuoka, Japan.
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2006 (Engelska)Ingår i: Molecular Microbiology, ISSN 0950-382X, E-ISSN 1365-2958, Vol. 59, nr 1, s. 99-112Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The α-haemolysin is an important virulence factor commonly expressed by extraintestinal pathogenic Escherichia coli. The secretion of the α-haemolysin is mediated by the type I secretion system and the toxin reaches the extracellular space without the formation of periplasmic intermediates presumably in a soluble form. Surprisingly, we found that a fraction of this type I secreted protein is located within outer membrane vesicles (OMVs) that are released by the bacteria. The α-haemolysin appeared very tightly associated with the OMVs as judged by dissociation assays and proteinase susceptibility tests. The α-haemolysin in OMVs was cytotoxically active and caused lysis of red blood cells. The OMVs containing the α-haemolysin were distinct from the OMVs not containing α-haemolysin, showing a lower density. Furthermore, they differed in protein composition and one component of the type I secretion system, the TolC protein, was found in the lower density vesicles. Studies of natural isolates of E. coli demonstrated that the localization of α-haemolysin in OMVs is a common feature among haemolytic strains. We propose an alternative pathway for the transport of the type I secreted α-haemolysin from the bacteria to the host cells during bacterial infections.

Ort, förlag, år, upplaga, sidor
Hoboken, NJ, United States: Wiley-Blackwell , 2006. Vol. 59, nr 1, s. 99-112
Nyckelord [en]
Escherichia coli, OMVs, outer membrane vesicles, haemolysin, UPEC
Nationell ämneskategori
Mikrobiologi inom det medicinska området
Forskningsämne
molekylärbiologi
Identifikatorer
URN: urn:nbn:se:umu:diva-27736DOI: 10.1111/j.1365-2958.2005.04938.xOAI: oai:DiVA.org:umu-27736DiVA, id: diva2:277437
Anmärkning
Stina Berglund nu Stina LindbergTillgänglig från: 2009-12-08 Skapad: 2009-11-18 Senast uppdaterad: 2018-06-08Bibliografiskt granskad
Ingår i avhandling
1. Molecular analysis of transcription factors in uropathogenic E. coli adhesin operons
Öppna denna publikation i ny flik eller fönster >>Molecular analysis of transcription factors in uropathogenic E. coli adhesin operons
2009 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Alternativ titel[sv]
Molekylär analys av transkriptionsfaktorer i adhesin operon hos uropatogena E. coli
Abstract [en]

The main causative agent of human urinary tract infections is the uropathogenic Escherichia coli (UPEC) pathotype. It may cause disease due to its ability to express a number of bacterial virulence factors. Fimbrial adhesins are particularly important for the initial establishment of infection in the urinary tract. The fimbriae are hair-like structures protruding from the bacterial cell and by attaching to specific receptors in the urinary tract they mediate adherence to different cell types, allowing the bacteria to resist the shear forces from urine flow. The UPEC strains generally carry multiple determinants for fimbrial adhesins. Previous studies have indicated that there is a co-regulation between different fimbrial genes and one factor that has been implicated in this is the PapB protein, acting as a transcriptional regulator of P-fimbrial expression. The PapB protein can be regarded as the prototype of a family of fimbrial regulators that show high homology between different fimbrial operons. One homolog is FocB, regulator of F1C fimbriae. In this study, the role of the FocB protein in the regulation of F1C fimbriae as well as in the co-regulation with other fimbrial genes was investigated. It was observed that FocB binds to DNA, similarly to PapB, in an oligomeric fashion and that PapB and FocB can form hetero-oligomeric complexes, which appear to have a repressive role in the regulation of the F1C fimbriae. In addition, the FocB protein also had a repressive effect on transcription of the fim operon, which encodes theType 1 fimbriae. For further analysis of FocB in vitro, we developed efficient procedures for purification of the protein and established conditions for its crystal formation with the aim to conduct X-ray diffraction studies. By the hanging-drop vapour-diffusion method, we obtained crystals that in the X-ray analysis diffracted sufficiently well to allow modelling of a high resolution structure of FocB. The structural model was considered in relation to the DNA binding properties of the protein. The FocB analysis represents the first structural model of this family of transcriptional factors. This model should aid in further understanding of the roles and functions of these proteins in the regulation of the UPEC fimbrial operons. The complexity of the system, with multiple factors involved in the regulation of fimbrial operons, was revealed in earlier studies of the PapI protein showing that PapI activates transcription of the pap operon as a part of a complex with the global regulator Lrp. However, PapI itself did not appear to bind to DNA and its mode of action has remained unclear. By genetic analyses and in vitro studies we show that PapI may interact also with the α subunit of the RNA polymerase. This finding indicates that PapI might directly interact with the transcriptional apparatus and thus aid in the activation of pap expression. Bacteria are frequently releasing outer membrane vesicles (OMVs) from their surface. We studied the release of the haemolysin toxin from E. coli in connection with formation of OMVs and found that the toxin was tightly associated with the vesicles in an active form. By overproduction of the PapB or PapI regulators in order to maximise the population of bacteria expressing fimbriae, we could detect P fimbriae proteins associated with OMVs that displayed specific adhesion to receptor-coated beads. This suggests a possible scenario in which the vesicles canfunction as directed vehicles of bacterial virulence factors.

Ort, förlag, år, upplaga, sidor
Umeå: Umeå Universitet, 2009. s. 63
Serie
Umeå University medical dissertations, ISSN 0346-6612 ; 1304
Nyckelord
UPEC, E. coli, F1C, P fimbriae, cross-talk, FocB, PapB, crystal structure, OMVs
Nationell ämneskategori
Mikrobiologi inom det medicinska området
Forskningsämne
molekylärbiologi
Identifikatorer
urn:nbn:se:umu:diva-27757 (URN)978-91-7264-879-1 (ISBN)
Disputation
2009-12-16, Major Groove, Institutionen för Molekylärbiologi, Byggn. 6L, Norrlands Universitetssjukhus, Umeå, 10:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2009-11-26 Skapad: 2009-11-19 Senast uppdaterad: 2018-01-12Bibliografiskt granskad

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