X-Ray studies of the ovomucoid-DHPC system

Complex of ovomucoid with 1,2 dihehadecyl-snglycero-3-phosphatidylcholine (DHPC) in water solution has been used as a model system for glycoprotein-lipid interactions.The structural parameters of this complex were determined with small angle-X-ray diffraction techniques. Knowing the repeat distance, the chemical composition of the association and the partial specific volumes of the components, the partial thickness of the glycoprotein, lipid and water layers can be determined and compared with the thickness of the lipid layers observed in pure lipid-water systems and lamellar associations in the absence of glycoprotein. The variation of the structural parameters at room temperature with the concentration of water was determined. Our results showed: the intersheet spacing increases from 112 to 157 Å, the thickness of the hydrocarbon chain layers decreases from 49 to 40Å and the thickness of glycoprotein layer increases from 62 to 100 Å. In this case the glycoprotein-lipid interaction appears to be of weak electrostatic nature and to involve mainly the polar regions of the structure. Fluorescence experiments have also been carried out to confirm the X-ray data.