The aerolysin membrane channel is formed by heptamerization of the monomer

The cytolytic toxin aerolysin has been found to form heptameric oligomers by SDS-PAGE electrophoresis, STEM mass measurements of single oligomers and image analysis of two-dimensional membrane crystals. Two types of crystal, flat sheets and long regular tubes, have been obtained by reconstitution of purified protein and Escherichia coli phospholipids. A noise-filtered image of the best crystalline sheets reveals a structure with 7-fold symmetry containing a central strongly stain-excluding ring that encircles a dark stain-filled channel 17 A in diameter. The ring is surrounded by seven arms each made up of two unequal sized domains. By combining projected views and side-views, a simplified model of the aerolysin channel complex has been constructed. The relevance of this structure to the mode of action of aerolysin is discussed.