Mechanism of membrane insertion of a multimeric beta-barrel protein: Perfringolysin O creates a pore using ordered and coupled conformational changes

Perfringolysin O, a bacterial cytolytic toxin, forms unusually large pores in cholesterol-containing membranes by the spontaneous insertion of two of its four domains into the bilayer. By monitoring the kinetics of domain-spe cific conformational changes and pore formation using fluorescence spectros copy, the temporal sequence of domain-membrane interactions has been establ ished. One membrane-exposed domain does not penetrate deeply into the bilay er and is not part of the actual pore, but is responsible for membrane reco gnition. This domain must bind to the membrane before insertion of the othe r domain into the bilayer is initiated. The two domains are conformationall y coupled, even though they are spatially separated. Thus, cytolytic pore f ormation is accomplished by a novel mechanism of ordered conformational cha nges and interdomain communication.