1.C.4.1.1
Aerolysin (β-hemolysin; cytolytic enterotoxin) precursor (Parker et al., 1994).  Upon transition  from the prepore to pore, the aerolysin heptamer shows a unique concerted swirling movement, accompanied by a vertical collapse of the complex, ultimately leading to the insertion of a transmembrane beta-barrel (Degiacomi et al. 2013).  Multiple conformational states lead to rotation of the core lysin to unleash the membrane spanning regions (Whisstock and Dunstone 2013).  Monomer activation, dependent on proteolysis, is the rate-limiting step for pore formation (Bischofberger et al. 2016). Cryo-electron microscopy structures of three conformational intermediates and the final aerolysin pore provide insight into the conformational changes that allow pore formation. The structures reveal a protein fold consisting of two concentric beta-barrels, tightly kept together by hydrophobic interactions. This fold suggests a basis for the prion-like ultrastability of aerolysin pore and its stoichiometry (Iacovache et al. 2016).