Effect of Peptide Insertion on the Physical Properties of Biological Model Membranes

As a consequence of an excessive and often inappropriate use of antibiotics in both human and animal health we are facing a world-wide, rapid increase in pathogenic bacteria, which are multiresistant to antibiotics. One emerging strategy is based on host defense peptides, which show in nature high specificity in their action towards their target cells. An understanding of the structure-function relationship of these peptides is the key for an industrial production of new antibiotics based on host defense peptides and ultimately to a medical application. The proposed project will elaborate a method to study for the first time peptide-membrane interactions in aligned samples in the fully hydrated state, i.e., under physiological relevant conditions. Measurements will be performed by utilizing x-ray diffraction. The planned studies are based on recent developments which have demonstrated that a) aligned multibilayers can be fully hyrated from water vapor, and that b) the two dimensional x-ray diffraction patterns contain direct information on the bilayer structure and pertinent mechanical parameters. The data analysis algorithm, capable of fitting the global x-ray diffraction pattern, will be developed to some extend in collaboration with John F. Nagle`s group (Carnegie Mellon University, Pittsburgh, USA). Once established, this will allow us to study the effects of peptide-membrane interactions by monitoring the physical properties of the bilayer. Thus we will use, for the first time, the bilayer itself as a probe to monitor the activity of the peptide. Experiments differ from previous studies on aligned samples, since they are performed at full hydration and further analyse the mechanical parameters of the membrane systems. Moreover, our method is very sensitive to small amounts of peptides - on the order of 1 mol% or less -compared to previous studies that had to use many moles of the peptide to get a tractable signal. If successful, we will be able to get a better understanding for example, of the mechanism of peptide induced pore formation under physiological conditions, thus, helping to settle current controversies on models for pore and antibiotic activity.