Laser-Raman investigation of phospholipid-polypeptide interactions in model membranes

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Abstract
The interaction of aqueous dimyristoylphosphatidylcholine liposomes with the polypeptides gramicidin A, poly-L-lysine, valinomycin and gramicidin S was investigated by laser-Raman spectroscopy. Auxiliary data were obtained from differential scanning calorimetry. Studies were carried out over the temperature range of 0-50.degree. C, encompassing the gel phase, the transition region and the liquid crystalline phase of the liposomes. Conformational changes in the phospholipid molecules were investigated by measuring the intensity of the 1062 cm-1 Raman band which is assigned to C-C stretching vibrations of trans segments. Three different types of phospholipid-polypeptide interactions were indicated by the observed Raman data. They were interpreted as orderly penetration of the phospholipid bilayer by a hydrophobic polypeptide; polar interactions involving primarily the head groups of the phospholipid; and disorderly hydrophobic binding between a polypeptide and the hydrocarbon domain of the phospholipid.

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