Molecular Interactions of an Ornithine-Rich pH-Responsive Self- Assembling Peptide with a Model Lipid Membrane: Conformational Aspects

Investigating interactions of designed peptide-based biomaterials with lipid membranes is important for applications in nanobiotechnology. Here the interaction of an ornithine-rich pH-responsive peptide called P11-5 with a model membrane was investigated employing Fourier transform infrared spectroscopy (FTIR). The results showed that in the range of pH 6.0-8.0 the peptide P11-5 shows spectral features which are evidence of the presence of peptides with antiparallel beta-sheet conformation (bands in the range 1625-1615 cm-1), as also spectral features which indicate the existence of random coil conformation (bands in the range 1640-1648 cm-1). Two types of membranes were used, 1,2- dipalmitoyl-sn-3-glycero-phosphocholine (DPPC) membranes with zwitterionic head groups and 1,2-dipalmitoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (sodium salt) (DPPG) membranes with anionic head groups. It was showed that there was a distinct peptide interaction under different pH values, pH 6.0, 7.0 and 8.0 for each type of lipid membrane with DPPC membrane preventing the peptide self-association even at basic pH, while for DPPG membrane there was a more evident peptide-lipid interaction. FTIR measurements indicate that in the presence of DPPC membrane the peptide was prevented to form beta-sheet aggregates at basic pH, while in the presence of DPPG membranes the self-association behavior of the peptide was more similar to its behavior when in aqueous solution in the absence of lipid membranes. Such results are important for the potential development of novel biomolecular nanostructured materials by the physico-chemical understanding of the peptide-lipid interactions.