Melittin-lipid interactions: a Ft-IR spectroscopic study
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In this research, the interaction of mellitin with dimyristoyl phosphatidyl-choline (DMPC) bilayers containing cholesterol was investigated by FT-IR spectroscopy at 25°C, after the gel to fluid phase transition but before the melting of the boundary layer. Results of experiments indicate that although the νa(CH2) and νs(CH2) modes of pure DMPC bilayers are found to shift to higher wavenumbers with the addition of melittin, these shifts are found to decrease by the addition of cholesterol to binary mixture of DMPC and melittin. The peak-hight intensity of the carbonly mode of the pure DMPC bilayer decreases by the addition of melittin. This perturbation is found to diminish in cholesterol containing DMPC/melittin bilayers. These results indicate that cholesterol's participation decreases protein-phospholipid interaction. On the other hand, although the half-band widths of the CH2 stretching modes are found to decrease in the IR spectra of melittin containing DMPC bilayers in comparison to those of pure DMPC bilayers, there are found to be not altered by the addition of cholesterol to melittin containing DMPC bilayers. The decrease of the half-band witdths of the CH2 stretching modes by the addition of melittin indicates that the melittin limits the total freedom of motion of the lipid acyl chains. This occurs despite the fact that more gauche conformers are introduced into the DMPC bilayer by the addition of melittin. Thus the spectroscopic results indicate that although the presence of cholesterol decrease the lipid-protein interaction, it does not affect the mobility of the chain if phospholipid bilayers contain protein.