Effect of glycophorin on lipid polymorphism: A 31P-NMR study

(1) The effect of glycophorin, a major intrinsic glycoprotein of the human erythrocyte membrane, on lipid polymorphism has been investigated by ³¹P-NMR (at 36.4 MHz) and by freeze-fracture electron microscopy. (2) Incorporation of glycophorin into vesicles of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) results in the formation of unilamellar vesicles (1000–5000 Å diameter) which exhibit ³¹P-NMR bilayer spectra over a wide range of temperature. A reduction in the chemical shift anisotropy (Δσ_csa^eff) and an increase in spectral linewidth in comparison to dioleoylphosphatidylcholine liposomes may suggest a decrease in phospholipid headgroup order. (3) 1,2-Dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), in the presence of excess water, undergoes a bilayer to hexagonal (H_II) phospholipid arrangement as the temperature is increased above 0°C. Incorporation of glycophorin into this system stabilizes the bilayer configuration, prohibiting the formation of the H_II phase. (4) Cosonication of glycophorin with DOPE in aqueous solution (pH 7.4) produces small, stable unilamellar vesicles (300–1000 Å diameter), unlike DOPE alone which is unstable and precipitates from solution. (5) The current study demonstrates the bilayer stabilizing capacity of an intrinsic membrane protein, glycophorin, most likely by means of a strong hydrophobic interaction between the membrane spanning portion of glycophorin and the hydrophobic region of the phospholipid.