On the mechanism of membrane damage by Staphylococcus aureus α-toxin

Abstract

Rabbit or human erythrocytes lysed with S. aureus α-toxin were solubilized with Triton X-100, and the toxin was subsequently isolated by gel chromatography, sucrose density gradient centrifugation, and reincorporation into liposomes. In the presence of Triton X-100, the toxin exhibited a sedimentation coefficient of 11S and eluted at a position between those of IgG and α2-macroglobulin in gel chromatography. A single polypeptide subunit of 34,000 mol wt was found in SDS PAGE. In the electron microscope, ring-shaped or cylindrical structures were observed, 8.5-10 nm in diameter, harboring central pits or channels 2-3 nm in diameter. An amphiphilic nature of these structures was evident from their capacity to bind lipid and detergent, aggregation in the abscence of detergents, and low etlutability from biological and artifical membranes through ionic manipulatons. In contrast to the membrane-derived form of α-toxin, native toxin was a water-soluble, 34,000 mol wt, 3S molecule, devoid of an annular structure. Because studies on the release of radioactive markers from resealed erythrocyte ghosts indicated the presence of circumscribed lesions of -3-nm effective diameter in toxin-treated membranes, the possibility is raised that native α-toxin oligomerizes on and in the membrane to form an amphiphilic annular complex that, through its partial embedment within the lipid bilayer, generates a discrete transmembrane channel.