The role of cholesterol and glycosylphosphatidylinositol-anchored proteinsof erythrocyte rafts in regulating raft protein content and malarial infection

Human erythrocytes are terminally differentiated, non-endocytic cells that lack all intracellular organelles. Here we show that their plasma membranes contain detergent-resistant membrane rafts that constitute a small fractio n (4%) of the total membrane protein, with a complex mixture of proteins th at differentially associate with rafts. Depletion of raft-cholesterol abrog ates association of all proteins with no significant effect on cholesterol: protein ratios in the rest of the membrane, lipid asymmetry, deformability, or transport properties of the bilayer, indicating that cholesterol is cri tical for protein assembly into rafts and suggesting that rafts have little influence on several erythrocyte functions. Erythrocytes from patients wit h paroxysmal nocturnal hemoglobinuria, which lack glycosylphosphatidylinosi tol-anchored proteins, show significant elevation in raft-cholesterol but n o increase in raft protein association, suggesting that raft assembly does not require glycosylphosphatidylinositol-anchored proteins, raft proteins d o not bind directly to cholesterol, and only threshold levels of raft-chole sterol are critical for protein recruitment. Loss of glycosylphosphatidylin ositol-anchored proteins had no effect on erythrocytic infection by malaria l parasite or movement of raft markers into the parasite's vacuole. However , infection is blocked following raft-cholesterol disruption, suggesting th at erythrocyte rafts can be functionally exploited and providing the first evidence for the involvement of host rafts in an apicomplexan infection.