INTERACTION OF APOPROTEIN FROM PORCINE HIGH-DENSITY LIPOPROTEIN WITH DIMYRISTOYL LECITHIN .1. STRUCTURE OF COMPLEXES

The morphology and structural organization of the complexes formed from the apoprotein of porcine high-density lipoprotein and dimyristoyl phosphatidylcholine (lecithin) were studied using the technique of small-angle X-ray scattering. Scattering measurements made in solvents of varying electron density were interpreted in terms of a scattering-equivalent model for the structure of the complex. This model is described by an oblate ellipsoidal morphology with dimensions at 20.degree. C: major axis 11.0 nm, minor axis 5.5 nm. Within this overall shape the lipid hydrocarbon chains are organized in an apolar core while the lipid polar head groups and protein are located in an outer shell 0.85 nm in thickness. The oblate morphology demonstrates that the structure of the conplex is directed by the fundamental bilayer organization of the lecithin. The dimension of the minor axis (5.5 nm) indicates that phospholipid hydrocarbon chains are orientated perpendicular to the interface.