Interaction of Apoprotein from Porcine High-Density Lipoprotein with Dimyristoyl Lecithin. 2. Nature of Lipid-Protein Interaction

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Abstract
The detailed molecular structure of the complex formed by the apoprotein from porcine high density lipoprotein and dimyristoyl phosphatidylcholine (lecithin) has been investigated by a range of physical techniques. The complex, an oblate ellipsoid with major axis 11.0 nm and minor axis 5.5 nm (see the accompanying paper), is comprised of a section of lecithin bilayer with apoprotein at the surface. The main site of interaction between protein and lipid is in the lipid glycerophosphorylcholine group region; as with native high density lipoprotein the surface of the particle consists of a mosaic of lecithin polar groups and protein. The formation of this mosaic reduces the cooperativity of the lecithin chain motions and changes the curvature of the lipid‐water interface, as compared to a bilayer. Otherwise, there are no major changes in lecithin motions indicating that no strong binding of lipid to protein occurs. The interaction involves the intercalation of amphipathic, 60%α‐helical, apoprotein molecules among the lecithin molecules so that the protein resides at the lipid‐watet interface. The apoprotein has a high affinity for the lipid‐water interface but specific lipid‐protein interactions are not involved.