Structure and interaction with model membranes of a CNBR peptide of diphtheria toxin B fragment

The mechanism by which diphtheria toxin (DT) crosses the endosomal membrane to exert its biological activity in the cell cytoplasm is still poorly understood. By measuring the change in conductance of planar lipid bilayers induced by cyanogen bromide peptides of fragment B of DT, we have identified a domain that could be involved in the pH-dependent membrane interaction of DT. Moreover, infrared spectroscopy has allowed us to demonstrate that, at low pH, in the presence of a lipid bilayer, this domain is mainly helical with the axis of the helices oriented parallel to the lipid acyl chains. On the basis of these results, we have designed mutants of DT which should provide information about the molecular mechanism of the DT membrane translocation process.