<p> This family represents the pore forming lobe of aerolysin, and the related toxins haemolysin and the leukocidin S subunit. </p><p>Aerolysin [<cite idref="PUB00002061"/>] is a cytolytic toxin exported by <taxon tax_id="644">Aeromonas hydrophila</taxon>, a Gram-negative bacterium associated with diarrhoeal diseases and deep wound infections [<cite idref="PUB00004166"/>]. The mature toxin binds to eukaryotic cells and aggregates to form holes (approximately 3 nm in diameter) leading to the destruction of the membrane permeability barrier and osmotic lysis. The structure of proaerolysin has been determined to 2.8A resolution and shows the protoxin to adopt a novel fold [<cite idref="PUB00004166"/>]. Images of an aerolysin oligomer derived from electron microscopy have helped to construct a model of the protein and to outline a mechanism by which it might insert into lipid bilayers to form ion channels [<cite idref="PUB00004166"/>].</p>