Carbon-13 nuclear magnetic resonance studies on the interaction of glycophorin with lecithin in reconstituted vesicles

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Abstract
Glycophorin, the MN blood group substance, is a major intrinsic glycoprotein in erythrocyte membranes. The interaction of glycophorin with phosphatidylcholine, 13C-labeled in specific positions in reconstituted unilamellar vesicles, was investigated by using the 13C NMR technique. 1-Palmitoyl-2-([14-13C]linoleoyl)-sn-glycero-3-phosphocholine was synthesized and used as a probe. At 37.degree. C the spin-lattice relaxation time (T1) of vesicle bilayers consisting of this phospholipid was 0.74 in the absence of glycophorin. The incorporation of glycophorin decreased the T1 to 0.63 s, indicating that the bulk lipid molecules are immobilized by glycophorin. In addition to the reduction in time, a broad component (.DELTA.H1/2 = .apprx. 40 Hz) superimposing the sharp resonance was observed in the 13C NMR spectrum of reconstituted vesicles. The T1 of the broad component was 0.32 s, suggesting that the lipid molecules contributing to the broad component may be more restricted than that of the sharp component. In order to quantify the broad component, a computer simulation was performed. The intensity of the broad component estimated from the simulation depended linearly on the concentration of glycophorin. The broad component is considered to be contributed by a phospholipid domain surrounding the glycophorin molecules, a boundary lipid. The relationship between the broad component and the stoichiometry of the reconstituted vesicles indicates that about 30 lipid molecules are immobilized by 1 glycophorin monomer.