Assembly of Staphylococcus aureus leukocidin into a pore-forming ring-shaped oligomer on human polymorphonuclear leukocytes and rabbit erythrocytes

Staphylococcal leukocidin consists of two separate proteins, LukS and LukF, which cooperatively lyse human and rabbit polymorphonuclear leukocytes and rabbit erythrocytes. Here we studied the pore-forming properties of leukocidin and the molecular architecture of the leukocidin pore. (1) Leukocidin caused an efflux of potassium ions from rabbit erythrocytes and swelling of the cells before hemolysis. However, ultimate lysis of the toxin-treated swollen erythrocytes did not occur when polyethylene glycols with hydrodynamic diameters of greater than or equal to 2.1 nm were present in the extracellular space. (2) Electron microscopy showed the presence of a ring-shaped structure with outer and inner diameters of 9 and 3 nm, respectively, on leukocidin-treated human polymorphonuclear leukocytes and rabbit erythrocytes. (3) Ring-shaped structures of the same dimensions were isolated from the target cells, and they contained LukS and LukF in a molar ratio of 1:1. (4) A single ring-shaped toxin complex had a molecular size of 205 kDa. These results indicated that LukS and LukF assemble into a ring-shaped oligomer of approximately 200 kDa on the target cells, forming a membrane pore with a functional diameter of approximately 2 nm.