Localization in diphtheria toxin fragment B of a region that induces pore formation in planar lipid bilayers at low pH

Like diphtheria toxin and the N-terminal (M_r 23 000) region of fragment B, CB1 (M_r 13 000), the cyanogen bromide peptide located in the middle region of fragment B is able to induce pore formation in lipid bilayer membrane at low pH. These two peptides (M_r 23 000 and 13 000) share a common segment (M_r 6300) containing the predicted amphipathic, -helical, transverse lipid-associating domain (M_r 2750) of fragment B[J. Cell Biol. (1980) 87, 837–840]. Therefore, we postulated this domain to be responsible for the pore formation ability of diphtheria toxin [Proc. Natl. Acad. Sci. USA (1981) 78, 172–176]. A relationship between the pH dependency of pore formation and the presence of a cluster of prolines in the C-terminal region of CB1 is proposed.