Channel formation by the glycosylphosphatidylinositol-anchored protein binding toxin aerolysin is not promoted by lipid rafts

Glycosylphosphatidylinositol-anchored proteins may be concentrated in membr ane microdomains (lipid rafts) that are also enriched in cholesterol and sp hingolipids. The glycosyl anchor of these proteins is a specific, high affi nity receptor for the channel-forming protein aerolysin. We wished to deter mine if the presence of rafts promotes the activity of aerolysin, Treatment of T lymphocytes with methyl-beta-cyclodextrin, which destroys lipid rafts by sequestering cholesterol, had no measurable effect on the sensitivity o f the cells to aerolysin; nor did similar treatment of erythrocytes decreas e the rate at which they were lysed by the toxin. We also studied the rate of aerolysin-induced channel formation in liposomes containing glycosylphos phatidylinositol-anchored placental alkaline phosphatase, which we show is a receptor for aerolysin. In liposomes containing sphingolipids as well as glycerophospholipids and cholesterol, most of the enzyme was Triton X-100-i nsoluble, indicating that it was localized in rafts, whereas in liposomes p repared without sphingolipids, all of the enzyme was soluble. Aerolysin was no more active against liposomes containing rafts than against those that did not. We conclude that lipid rafts do not promote channel formation by a erolysin.