Question

binding and partial inactivation of staphylococcus aureus alpha toxin by human plasma low density lipoprotein

Answer 1

Human low density lipoprotein (LDL) in isolated form or in unfractionated serum binds and partially inactivates Staphylococcus aureus α-toxin. Under conditions of LDL excess, up to 90% inactivation occurs as estimated by hemolytic titration. Inactivation is accompanied by, and probably due to, oligomerization of 3 S native toxin molecules into 11 S hexamers on the LDL molecules. This process is believed to be mediated by the lipids contained in the lipoprotein. The toxin hexamers are visualized as ring structures and stubs bound to the spherical LDL molecules by negative staining electron microscopy. These structures appear identical with those formed on target erythrocyte membranes during toxin-dependent lysis. The toxin hexamers are trypsin-resistant and do not spontaneously dissociate from the lipoprotein.