Interaction of a pH-responsive designed nanostructured peptide with a model lipid membrane

Studying molecular interactions of soft biomolecular materials is a key step to the development of novel functional nanostructures with potential application in nanobiotechnology and nanomedicine. In current work we aimed to study the interaction of a rationally designed peptide whose degree of molecular self-association depends on pH, with model membranes employing Fourier transform infrared spectroscopy (FTIR). Two types of model lipid membranes were used, one formed by the DPPC, a lipid with a zwitterionic head group, and consequently electrically neutral, and the other type formed by the DPPG, a lipid with an anionic head group, and therefore negatively charged. The results showed that in the range of pH 6.0-8.0 the peptide P11-4 shows spectral features which are evidence of the presence of peptides with anti-parallel beta-sheet conformation (bands in the range 1625-1615 cm-1 and 1680-1685 cm-1, as also spectral features which indicate the existence of random coil conformation (bands around 1644 cm-1). According to the results obtained by FTIR, it was found that the peptide had its behavior modulated by the interaction with the model membranes. It was observed that DPPG model lipid membranes caused an effect on P11-4 molecular organization state under different pH values, pH 6.0, 7.0 and 8.0, showing the most prominent effect on the basic environment, while the DPPC membranes practically did not affect the peptide self-assembling behavior. Such results are important for the development of novel biomolecular nanostructured materials by the physico-chemical understanding of self-organizing molecular systems.