We have investigated the interaction of lipoproteins with liposomes to form recombinant particles. A number of lipoprotein fractions (VLDL, IDL, LDL, and HDL) all disrupt liposome structure by an essentially irreversible and quasistoichiometric process. In the case of HDL, the major apoprotein, A-I, recombines with dimyristoyl phosphatidyl choline vesicles 40:1 lipid-protein to form discs approximately 100 Angstroms in diameter and 32 Angstroms in thickness, with protein on the rim. These structural results were obtained by a combination of neutron scattering, electron microscopy, column chromatography, and fluorescence techniques. With dipalmitoyl phosphatidylcholine, A-I also forms what we term """"""""vesicular recombinant"""""""" particles in a process which may relate to physiological mechanisms by which proteins are assembled into membranes and lipoproteins. To study this process we have developed a technique called """"""""phase transition release"""""""" (PTR) which is also being applied to study incorporation of tubulin into membranes. Lipoproteins were labelled with the fluorescent lipid 3,3 dioctadecylindocarbocyanine for studies of interaction will cell surface lipoprotein receptors. The lipoproteins are also being labelled with NBD lipids for two-color fluorescence identification of cells in atheroscleroic plaques. Lipid membrane systems are being used to investigate the interaction between characterized synthetic antigenic peptides and T-cell recognition of antigens.
