STRUCTURE AND ORIENTATION OF APO-B-100 PEPTIDES INTO A LIPID BILAYER

Peptides corresponding to lipid binding domains of Apo B-100 were synt hesized, purified, and incubated with dimyristoylphosphatidylcholine ( DMPC) liposomes. The secondary structure of the apo B-100 peptide-lipi d complexes was evaluated by attenuated total reflection Fourier trans form infrared spectroscopy (ATR-FTIR). Those peptides belonging to the hydrophobic ''core'' domain of apo B-100 when associated with phospho lipids were rich in sheet structure; a predominant alpha helical confo rmation was shown to be associated with one peptide located in a surfa ce region of apo B-100. IR dichroic spectra revealed, in the case of t he ''core'' peptides, that the beta sheet component is the only orient ed structure with respect to the phospholipid acyl chains. This orient ation of the beta sheet was recently found in LDL particles after prot eolytic digestion by trypsin (Goormaghtigh, E., Cabiaux, V., De Meutte r, J., Rosseneu, M., and Ruysschaert, J. M., 1993, Biochemistry 32, 61 04-61 10). Altogether, the data suggest that beta sheet, present in a high proportion in the native apo B-100, is probably another protein s tructure in addition to the amphipathic helix which strongly interacts with the lipid outer layer surrounding the LDL particle.