Compositional and stoichiometric analysis of Clostridium perfringens enterotoxin complexes in Caco-2 cells and claudin 4 fibroblast transfectants

Clostridium perfringens enterotoxin (CPE) binds to host cell receptors, forming a small complex precursor for two large complexes reportedly having molecular masses of similar to 155 or similar to 200 kDa. Formation of the similar to 155 kDa complex causes a Ca2+ influx that leads to apoptosis or oncosis. CPE complex composition is currently poorly understood, although occludin was identified in the similar to 200 kDa complex. The current study used heteromer gel shift analysis to show both CPE large complexes contain six CPE molecules. Ferguson plots and size exclusion chromatography re-sized the similar to 155 and similar to 200 kDa complexes as similar to 425-500 kDa and similar to 550-660 kDa respectively. Co-immunoprecipitation and electroelution studies demonstrated both CPE-binding and non-CPE-binding claudins are associated with all three CPE complexes in Caco-2 cells and with small complex and similar to 425-500 kDa complex of claudin 4 transfectants. Fibroblast transfectants expressing claudin 4 or C-terminal truncated claudin 4 were CPE-sensitive and formed the similar to 425 kDa complex, indicating claudin-induced cell signalling is not required for CPE action and that expression of a single receptor claudin suffices for similar to 425-500 kDa CPE complex formation. These results identify CPE as a unique toxin that combines with tight junction proteins to form high-molecular-mass hexameric pores and alter membrane permeability.