Investigation of shot peptide action on lamellar phases

Full text: The incorporation of proteins, peptides to lipid bilayers affect their mechanical properties as well as their three-dimensional organization. It has been shown that peptides, at low concentrations, are adsorbed at interface with little disturbing effects on membrane elasticity. Above a given concentration, the peptides self assembly in more complex structures, like filaments and fibrils inducing the formation of pores and eventually membrane disruption. In this work we investigate the effect of a small sequence of amino acids, diphenylalanine (FF), on lamellar phases composed of soy lecithin. This sequence is particularly interesting due to their ability to self-assemble in nanotubes and nanowires and are part of a longer sequence (LVFFA) found in in patients with Alzheimer's disease. The peptide was co-solubilized with lecithin and then dispersed in water to form lamellar phases. The effect of the peptide on the elasticity of lipid bilayers was explored using X-ray scattering and microscopy techniques.The molar ratio between peptide and the lecithin (P/L) was varied from 0.2 to 0.001, for it one composition was varied the volume fraction of water between 0.8 to 0.25. In the Small Angle X-ray Scattering (SAXS) data for all studied P/L we observed a lamellar phase and geometric parameters such as periodicity and thickness of the lamellar bilayer and thermodynamic (Caill ́e parameter) were obtained from the fitting curves. The lamellar periodicity is not altered with the increase of the peptide concentration when compared to the behavior of pure lecithin, however, other structural parameters, such as Caill ́e parameter and electronic thickness, are influenced by the incorporation of the peptide in the lamellar phase. The Wide-angle X-ray scattering (WAXS) data we observed a fluid lamellar phase and when increase P/L ratio appear Braggs peaks correlated of the formation of amyloid fibers. (author)