Cellular uptake of the Clostridium perfringens binary iota-toxin

The binary iota-toxin is produced by Clostridium perfringens type E strains and consists of two separate proteins, the binding component iota b (98 kD a) and an actin-ADP-ribosylating enzyme component iota a (47 kDa), Iota b b inds to the cell surface receptor and mediates the translocation of iota a into the cytosol. Here we studied the cellular uptake of iota-toxin into Ve ro cells. Bafilomycin A1, but not brefeldin A or nocodazole, inhibited the cytotoxic effects of iota-toxin, indicating that toxin is translocated from an endosomal compartment into the cytoplasm. Acidification (pH less than o r equal to 5.0) of the extracellular medium enabled iota a to directly ente r the cytosol in the presence of iota b, Activation by chymotrypsin induced oligomerization of iota b in solution. An average mass of 530 +/- 28 kDa f or oligomers was determined by analytical ultracentrifugation, indicating h eptamer formation. The entry of iota-toxin into polarized CaCo-2 cells was studied by measuring the decrease in transepithelial resistance after toxin treatment. Iota-toxin led to a significant decrease in resistance when it was applied to the basolateral surface of the cells but not following appli cation to the epical surface, indicating a polarized localization of the io ta-toxin receptor.