Bacterial alpha-hemolysin toxin, molecular model. This toxin is secreted by the bacterium Staphylococcus aureus. It is an example of a pore-forming toxin, forming pores in the membranes of affected cells, damaging or killing them (making it a cytolytic protein). This toxin forms a heptameric (seven-part) transmembrane pore. Seven protein chains form the outer beta barrel-type pore, with an inner, smaller barrel inside the outer one. The overall structure is mushroom-shaped.