Interaction of Melittin with Phospholipid- and Lipopolysaccharide- Containing Model Membranes

Abstract

Up to now the details of the mechanisms of melittin action on biological bilayer model sys- tems in dependence on lipid composition, in particular on the kind of head groups, temperature, and ionic strength are not well understood. In particular, the influence of cholesterol present in most eu- caryotic cells and the influence of glycolipids present in bacterial membranes are far from being clear. Here, data are presented from investigations by small-angle X-ray scattering (SAXS), Fourier- transform infrared spectroscopy (FTIR), circular dichroism (CD) spectroscopy, Forster resonance electron transfer (FRET) spectroscopy, and calorimetric techniques (DSC: differential scanning calorimetry and ITC: isothermal titration calorimetry) on the interaction of melittin with different (glyco)lipids, in order to elucidate 1) the peptide secondary struc- ture during the melittin-lipid interaction, 2) to monitor the intercalation of the peptide into membranes, 3) to characterize the aggregate structure of the lipids, 4) to characterize the influence of lipid:melittin ratio with regard to the acyl chain melting behaviour as well as 5) to determine the peptide-lipid binding stoichiometry. These experiments are correlated with results from biological test systems, in which the inhibition of the lipopolysaccharide-induced cytokine expression in human immune cells by melittin was monitored. Furthermore, the findings are related to data found in literature with various membrane systems and different techniques. In this way, it is now possible to better understand the details of the melittin-membrane interactions, which is important with respect to the understanding of its anti-inflammatory and antimicrobial properties.