Bifactorial versus monofactorial molecular status of Staphylococcus aureus γ-toxin

The extracellular Staphylococcus aureus γ-toxin (hemolysin) released by the Smith 5R strain has been purified (M, 38 kDa, pl 9.55). We established that this cytolysin is a single polypeptide fully lytic on rabbit erythrocytes. In contrast, this toxin alone was unable to lyse other cells and was required to act jointly with an accessory 58 kDa protein released by the same strain. This protein, named sensitizing protein (SP), was required in order to damage the cytoplasmic membranes of other red blood cells including human erythrocytes as well as that of other eukaryotic cells (Jurkat and Hep-2). The lytic process can be referred to as conditional synergistic or cooperative lysis. γ-toxin, and SP were also found able to disrupt phospholipid/cholesterol containing liposomes. We demonstrated that a minor membrane phospholipid, phosphatidylinositol, is crucial for γ-toxin binding to cells and/or channel formation through membrane lipid bilayer.