A polylysine-polyhistidine fusion peptide for lysosome-targeted protein delivery

Cell-penetrating peptides (CPPs) can deliver payloads into cells by forming complexes with bioactive molecules via either covalent or non-covalent bonds. Previously, we reported polyhistidine (H16 peptide: HHHHHHHHHHHHHHHH-NH₂) as a new CPP. This peptide is anticipated to be a valuable new carrier for drug delivery to intracellular lysosomes; the peptide can transport macromolecules into these organelles. In the present study, we examined the application of the H16 peptide as a drug delivery system (DDS) to reverse to lysosomal storage disease (LSD) in cells in vitro. LSDs are metabolic disorders caused by the loss of specific lysosomal enzymes. The majority of lysosomal enzymes are acidic proteins and we utilized this common feature for our DDS. We synthesized a polylysine-polyhistidine fusion peptide (K10H16 peptide: KKKKKKKKKKGHHHHHHHHHHHHHHHH-NH₂) and developed a simple method for transporting acidic proteins into intracellular lysosomes via formation of complexes of enzymes with the K10H16 peptide by electrostatic interaction. First, we demonstrated our strategy using maltose-binding protein-fused green fluorescent protein (MBP-GFP) to model an acidic protein. The K10H16 peptide bound to MBP-GFP and transported it into intracellular lysosomes. Further, alpha-galactosidase A (GLA), one of the lysosomal enzymes associated with LSD, was also delivered to intracellular lysosomes by the peptide. The complex between K10H16 peptide and GLA restored typical proliferation to LSD cells, which otherwise grew more slowly than normal cells. These results suggest that K10H16 peptide replenished lysosomal enzyme deficiency in LSD cells. The K10H16 peptide may be useful as a DDS for LSD therapy.