Pressure effects on the structure and phase behaviour of phospholipid-gramicidin bilayers

The influence of Gramicidin D (GD) incorporation on the structure and phase behaviour of aqueous dispersions of fully hydrated neutral phospholipid bilayers of 1,2-dipahnitoyl-sn-glycero-3-phosphatidylcholin (DPPC) has been studied using differential scanning calorimetry, small-angle x-ray scattering and H-2-NMR spectroscopy. The experiments covered a temperature range of 0 - 80 degreesC 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. Small-angle x-ray scattering was used to detect 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. H-2-NNM spectroscopy yields further information on the conformation and dynamics of the lipid acyl chains by measuring the molecular chain order parameters and spectral moments.