Fragment A of diphtheria toxin causes pH-dependent lesions in model membranes.
Fragment A of diphtheria toxin has been shown to insert into lipid bilayers at low pH (Montecucco, C., Schiavo, G., and Tomasi, M. (1985) Biochem. J. 231, 123-128; Zhao, J.-M., and London, E. (1988) J. Biol. Chem. 263, 15369-15377). In this report, evidence is provided which demonstrates that fragment A, like diphtheria toxin, can also cause the release of a fluorescent dye (calcein) from vesicles under acidic conditions and that this release parallels fragment A insertion into the membrane. Although the permeability changes are not as large as those obtained with whole toxin (Jiang, G.-S., Solow, R., and Hu, V. W. (1989) J. Biol. Chem. 264, 13424-13429), molecular sieving experiments indicate that the lesion induced by fragment A increases in size with decreasing pH and reaches an upper limit of 30 A at pH 4.0. In addition to size differences, the lesion induced by fragment A releases calcein in a graded manner, whereas diphtheria toxin causes an all-or-none release. One possible interpretation of this result is that the fragment A lesion is transient in comparison to that induced by whole toxin. Although the molecular bases for the observed differences are not understood, these data suggest that fragment A interaction with the lipid bilayer may play a significant role in mediating its own translocation across membranes and that fragment B may aid this process by initiating, enlarging, and stabilizing the lesion formed.
Jiang
G S
GS
Department of Biochemistry and Molecular Biology, George Washington University Medical Center, Washington, D.C. 20037.
Solow
R
R
Hu
V W
VW
D002118:Calcium / Q000378:metabolism; D002463:Cell Membrane Permeability; D002850:Chromatography, Gel; D004167:Diphtheria Toxin / Q000378:metabolism / Q000494:pharmacology*; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers / Q000378:metabolism; D008081:Liposomes / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism / Q000494:pharmacology*
D004167:Diphtheria Toxin; D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D008081:Liposomes; D010446:Peptide Fragments; C029795:diphtheria toxin fragment A; D002118:Calcium