Highly lipid-soluble α-helical amphiphilic cell-penetrating peptide used in combination with phospholipids for developing pulmonary surfactant model systems. Hel 13-5 also binds to nucleic acids. The CPP is a most efficient DNA and siRNA delivering and transfecting agent.Hel 13-5 is a cell-penetrating peptide that contains Leu and Lys residues in the ratio of 13:5. It binds to DNA and forms alpha-helical structures. It is used as an efficient way for gene transfer into cells and DNA transfection.