Direct extraction of A and B blood group antigens from human red cells by liposomes

Mechanism of selective release of membrane proteins from human erythrocytes in the presence of liposomes

Incubation of erythrocytes with liposomes results in the release of shed vesicles rich in glycosyl-phosphatidylinositol (GPI)-anchored proteins but poor in transmembranous proteins. We investigated the mechanisms of membrane protein polarization by examining the effect of the interaction between spectrin and membrane proteins on the release of a transmembranous protein, band 3, and a GPI-anchored protein, acetylcholinesterase (AChE), from erythrocyte ghosts. Polymerization of spectrin resulted in a 30-fold decrease in the released amount of band 3 per constant amount of shed vesicles but did not affect the amount of released AChE per constant amount of shed vesicles. On the other hand, the amount of released band 3 per constant amount of shed vesicles increased by cleaving the cytoplasmic part of band 3. Our results first demonstrated that the diffusibility of membrane proteins determined by steric hindrance between membrane proteins and protein mesh primarily determines the ease of localization of membrane proteins into shed vesicles. Taken together with the recent biophysical studies, we built a "fence selection model" that retrograding spectrin mesh sweeps diffusing band 3 molecules from the tip of the membrane crenated area toward the entry of the crenated area, but not AChE molecules. Our study describes a novel method for isolation of a large number of vesicles containing special and intact membrane proteins from cells not by using detergents or organic solvents, but by utilizing the fence effect between the cytoskeleton and membrane proteins.