1-2-dilauroylphosphatidylcholine and dimyristoylphosphatidylglycerol

We describe a method of measuring neutron scattering of aligned membranes with the momentum transfer oriented parallel or partly perpendicular to the plane of the membranes. The method obtains the complete information for the structures within fluid membranes obtainable by scattering. Data from alamethicin- and magainin-induced pores are presented. Although the in-plane scattering curves of these two peptides are similar to each other, their off-plane scattering patterns are strikingly distinct. Magainin pores exhibit intermembrane correlations.

Topics: Alamethicin; Dimyristoylphosphatidylcholine; Liposomes; Membrane Fluidity; Models, Biological; Neutrons; Peptides; Phosphatidylcholines; Phosphatidylglycerols; Scattering, Radiation

Circular dichroism measurements were carried out on poly(L-lysine) in the presence of vesicles of the negatively charged phospholipids, phosphatidylserine (PS; from bovine brain), phosphatidic acid (PA; prepared from egg yolk lecithin) and dimyristoylphosphatidylglycerol (DMPG). PS vesicles induced a conformational change in poly(L-lysine) from random coil to alpha-helix structure in 5 mM Tes (pH 7.0), whereas PA vesicles gave rise to beta-structure in the same buffer. The fraction of alpha-helix, F alpha (or beta-structure, F beta), increased with increasing PS (or PA) concentration, reaching a saturation value of about 0.7 (or about 1). Mixed vesicles comprising PS and dilauroylphosphatidylcholine (DLPC) also induced alpha-helix conformation, however, the saturation value of F alpha diminished with decreasing PS content in mixed vesicles. On the other hand, the spectral patterns for poly(L-lysine) in DMPG vesicle suspensions exhibited the coexistence of alpha-helix and beta-structure. Both F alpha and F beta increased with DMPG concentration and reached saturation values of about 0.5. Mixed vesicles composed of DMPG and dimyristoylphosphatidylcholine (DMPC) led to a reduction in F beta, while F alpha remained almost constant. The diversity in ordered structure induced by different phospholipid vesicles suggests the participation of lipid head groups in determining the secondary structure of poly(L-lysine) adsorbed on the vesicular surface.

Topics: Chemical Phenomena; Chemistry, Physical; Circular Dichroism; Phosphatidic Acids; Phosphatidylcholines; Phosphatidylglycerols; Phosphatidylserines; Polylysine; Protein Conformation