Pressure Effects on the Structure and Phase Behavior of Phospholipid–Polypeptide Bilayers – A Synchrotron Small-Angle X-ray Scattering and ²H-NMR Spectroscopy Study on DPPC–Gramicidin Lipid Bilayers

Abstract

The influence of gramicidin D (GD) incorporation on the structure and phase behavior of aqueous dispersions of fully hydrated phospholipid bilayers of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholin (DPPC) has been studied using small-angle X-ray scattering (SAXS) and ²H-NMR spectroscopy. The experiments covered a temperature range of 0–80 °C and a pressure range of 0.001–4 kbar. Pressure has been applied so as to be able to tune the lipid bilayer thickness at constant thermal energy and to select different gel phases, but also because high pressure is an important feature of certain natural membrane environments. SAXS was used to detect lipid bilayer topological changes upon incorporation of GD into the lipid bilayer. The data show that, depending on the GD concentration, the structure of the temperature- and pressure-dependent lipid phases is significantly altered by the insertion of the polypeptide, but also the lipid matrix has the ability to modulate the conformation of the inserted polypeptide. ²H-NMR spectroscopy yields further information on the conformation and dynamics of the lipid acyl-chains as a function of temperature, pressure and peptide concentration by measuring the molecular chain order parameters and spectral moments.