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.