Conformations of primary amphipathic carrier peptides in membrane mimicking environments

Two peptides designed for drug delivery were generated by the combination of a signal peptide with a nuclear localization sequence and are shown to facilitate the cellular internalization of small molecules which are covalently linked to these peptides. In order to understand the mechanism of internalization, the conformations of the peptides were investigated through different approaches both in solution and in membrane-mimicking environments. These peptides are highly versatile and adopt different conformational states depending on their environment. While in a disordered form in water, they adopt an alpha-helical structure in TFE and in the presence of micelles of SDS or DPC. The structured domain encompasses the hydrophobic part of the peptides, whereas the charged C-termini remain unstructured. In contrast, in the presence of lipids and whatever the nature of the phosphate headgroup, the two peptides mainly adopt an antiparallel beta-sheet form and embed in the lipidic cores. This result suggests that the beta-sheet is responsible for the translocation through the cellular membranes but also questions the conformational state of signal peptides when associated to hydrophilic sequences.