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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 21 (1996), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The diphtheria toxin (DT) membrane topology was investigated by proteolysis experiments. Diphtheria toxin was incubated with asolectin liposomes at pH 5 in order to promote its membrane insertion, and the protein domains located outside the lipid vesicles were digested with proteinase K (which is a non-specific protease). The protected peptides were separated by electrophoresis and identified by microsequence analysis. Their orientation with respect to the lipid bilayer and their accessibility to the aqueous phase were determined by attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR). These data, combined with those provided by proteolytic cleavage with a specific protease (endoproteinase Glu-C), led us to propose a topological model of the N-terminal part of the diphtheria toxin B fragment inserted into the lipid membrane. In this model, two a-helices adopt a transmembrane orientation, with their axes parallel to the lipid acyl chains, while a third o-helix could adopt a transmembrane topology only in a small proportion of DT molecules.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 11 (1994), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Diphtheria toxin (DT) is a bacterial protein that crosses the membrane of endosomes of target cells In response to the low endosomal pH. In this paper, we have inserted diphtheria toxin in asolectin vesicles at pH 5.0 and treated the reconstituted system with pronase. The peptides that were protected from digestion were separated by gel electrophoresls, transferred to a membrane and their N-terminal sequences were determined. All peptides belong to the B fragment of DT and cover residues 194–223, 266–375 and 429–528. The secondary structures of the peptides inserted in the membrane, determined by Fourier-transformed infrared spectroscopy, were shown to be mostly α-helices and β-sheets (44% and 53%, respectively). On the basis of these data and the recently published X-ray structure of DT, we are proposing a topology for the DTB fragment in the membrane.
    Type of Medium: Electronic Resource
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