Interaction of the lipid-associating domain of glycophorin with phospholipid bilayers.

The MN-blood group bearing glycoprotein of the human red cell membrane, glycophorin, has been shown to traverse the membrane in vivo such that the NH2-terminal portion is exposed to the external, and the COOH-terminal portion exposed to the cytoplasmic, mileiu. The intervening 23 residue lipid-associating domain (LAD) of glycophorin has been shown to have a unique overall hydrophobicity. The LAD of glycophorin can be obtained intact within an aqueous insoluble tryptic peptic, T(is). Under appropriate conditions (the reaction not being spontaneous), T(is) can be associated with phospholipid bilayers. Freeze fracture studies of T(is): phospholipid vesicles suggest that T(is) forms multimeric torus-shaped intramembranous structures 80 A in diameter with n greater than 4. The plot of T(is) concentration versus multimer density suggests there is a critical multimer concentration (CMC) for T(is) in phospholipid bilayers (L/P = 200/1). Various physico-chemical techniques such as pyrene fluorescence spectroscopy, differential scanning calorimetry, and ionic permeability were used to investigate the T(is)-lipid association. Results indicate that this system is an excellent one in which to study the boundary lipid phenomenon. In addition, T(is) association with lipid bilayers is being correlated with the natural state of glycophorin in the red cell membrane.