Positively Charged Surfactant-like Peptides Self-assemble into Nanostructures

A new type of surfactant peptide designed to mimic the properties of cationic lipid systems is described. These cationic surfactant peptides are approximately 2 nm in length with a cationic, hydrophilic head consisting of one to two residues of lysine or histidine followed by a hydrophobic tail of six alanine, valine, or leucine residues. In water, these surfactant peptides form ordered structures with dynamic behaviors. At pH below the pI values of the peptides, dynamic light scattering showed two distinct structural populations with average diameters of 50 nm (>95%) and 100-200 nm (<5%). Transmission electron microscopy visualization of quick-frozen samples revealed these populations to likely represent nanotubes and nanovesicles, respectively, showing great interplay between them. Above the pI, these structures are absent, having further self-assembled into large membranous sheets. These cationic surfactant peptides are distinct from other anionic surfactant peptides and have different applications, possibly being useful as carriers for encapsulation and delivery of a number of small water-insoluble molecules and large biological molecular systems, including negatively charged nucleic acids.