The effects of inhibitors upon pore formation by diphtheria toxin and diphtheria toxin T domain

The formation of pores by membrane-inserted diphtheria toxin is closely lin ked to the translocation of its catalytic chain across membranes. In this r eport a number of aromatic polyanionic molecules were identified that inhib it toxin-induced leakage of molecules from model membrane vesicles. One inh ibitor, Cibacron blue, totally blocked pore formation. Aniline blue and Fas t Green decreased the size of the molecule released by a given concentratio n of toxin. Amaranth appeared to reduce the maximal amount of leakage, with out greatly affecting the size of the molecule released at a given toxin co ncentration. Finally, Ponceau S and Cibacron brilliant red appeared to exhi bit a mixture of these various types of inhibition. The inhibitors neither prevented the conformational transition of the toxin to form a hydrophobic state at low pH, nor (with the exception of Cibacron Brilliant Red) appeare d to strongly inhibit toxin binding to model membranes. Additional experime nts showed release of trapped materials from model membranes by isolated T domain of the toxin was similar to that by whole toxin. The effects of inhi bitors on T domain induced release was also similar to that they have on wh ole toxin. Therefore, it is likely that the inhibition of pore formation by whole toxin involves inhibitor interaction with the T domain. The inhibito rs identified in this study may be helpful for development of agents that i nterfere with toxin action in vivo.