Interaction of Arginine-Rich Surfactant-like Peptide Nanotubes with Liposomes

The interaction of the surfactant-like peptide (SLP) RL bearing three cationic arginine residues with model liposomes is investigated in aqueous solution at various pH values, under conditions for which the SLP self-assembles into nanotubes. The structure of liposomes of model anionic lipid DPPG [1,2-dipalmitoyl--glycero-3-phospho-rac-(1-glycerol)], or zwitterionic lipid DPPE [1,2-dipalmitoyl--glycero-3-phosphoethanolamine] is probed using small-angle X-ray scattering and cryogenic-transmission electron microscopy. The unilamellar vesicles of DPPG are significantly restructured in the presence of RL, especially at low pH, and multilamellar vesicles of DPPE are also restructured under these conditions. The SLP promotes the release of cargo encapsulated in the vesicles as probed by calcein fluorescence, with notably higher release for anionic DPPG vesicles. Laurdan fluorescence experiments to probe membrane fluidity (lipid chain ordering) show that RL destabilizes the lipid gel phase, especially for anionic DPPG. This model nanotube-forming SLP has promise as a pH-sensitive release system for vesicle-encapsulated cargo.