Development of systems that effectively bring macromolecules into cytosol should be beneficial for the understanding of biological significance of cytosolic components by modulating their functions using macromolecules, and for developing therapeutic systems based on these understandings. Our laboratory developed a peptide “L17E” that delivers macromolecules into cytosol, by modifying the sequence of a hemolytic spider venom peptide M-lycotoxin^[1]. L17E is capable of efficiently delivering various bioactive proteins, including IgG, into cytosol. Specific recognition of cytosolic proteins and suppression of glucocorticoid receptor-mediated transcription were thus achieved using the targeting IgGs in the presence of L17E.

To improve the cytosolic delivery activity of L17E, we focused on the helical structure formation of the peptides dependent on endosomal pH decrease to more interact with membranes. We have succeeded in obtaining a peptide named “HAad”, by stepwise remodeling of L17E. HAad attained a significantly improved cytosolic delivery of various biomacromolecules including polydextran (a model macromolecule), IgG, and Cre recombinase. The process of creation of HAad and the results of assessing the properties of HAad by using cellular assays and physicochemical analyses are also reported.