Cholesterol Alone is Sufficient to Specifically Trigger Perfringolysin O Oligomerization and Prepore Formation

Perfringolysin O (PFO) is a pore‐forming toxin secreted by Clostridium perfringens. Upon encountering a cholesterol‐containing membrane, the toxin oligomerizes and spontaneously inserts into the bilayer to form a large pore (diameter ~300 Å). The C‐terminus of PFO (domain 4) mediates its initial binding to the membrane, and this binding triggers the structural rearrangements required to initiate the oligomerization of PFO monomers. Although significant progress has been made in characterizing PFO structural changes during pore formation, the mechanism by which cholesterol effects PFO binding to the membrane and pore formation remains unknown. Using multiple independent fluorescence techniques, we have found that PFO binds to cholesterol dispersed in aqueous solution in the same manner as to cholesterol‐containing liposomal membranes. The topography of domain 4 when bound to cholesterol aggregates is indistinguishable to that observed with membrane bilayers. Moreover, the binding of domain 4 to cholesterol aggregates triggers the same conformational change in a distant domain that occurs when PFO interacts with liposomes. These results reveal that cholesterol alone is sufficient to trigger the conformational changes required for oligomerization and pore formation, thereby indicating that direct PFO‐cholesterol interactions are involved in and required for effecting each stage of the PFO cytolytic mechanism. Supported by NIH (USA) AI 37657 and by the R. A. Welch Foundation.