Monomer-monomer interactions drive the prepore to pore conversion of a beta-barrel-forming cholesterol-dependent cytolysin.

Perfringolysin O (PFO), a cholesterol-dependent cytolysin, forms large oligomeric pore complexes comprised of up to 50 PFO molecules. In the present studies a mutant of PFO (PFO(Y181A)) has been identified that traps PFO in a multimeric prepore complex that cannot insert its transmembrane beta-hairpins and therefore cannot form a pore. Remarkably, PFO(Y181A) can be induced to insert its transmembrane beta-hairpins if functional PFO is incorporated into the PFO(Y181A) oligomeric prepore complex. Furthermore, the transition from prepore to pore appears to be an "all or none" process; partial insertion of the transmembrane beta-barrel does not occur. Therefore, cooperative interactions between the monomers of the prepore drive the prepore to pore conversion that results in the formation of the transmembrane beta-barrel.