Protein transduction domains (PTDs) are short basic peptide sequences present in many
cellular and viral proteins that mediate translocation across cellular membranes. PTDs have
become widely used as tools for the delivery of high M r polypetides, polynucleotides, or
nanoparticles to cells in culture; and even the transfer of cargo molecules to the tissue of live
animals has been reported. These cell-permeable peptides are functional when fused in-
frame to recombinant polypeptides or when chemically coupled to their cargo. The …