Pep-1 is a synthetic cell penetrating peptides (CPPs) that has successfully delivered a variety of proteins and other biopharmaceutical macromolecules to cells in a non-destructive manner. It is a kind of CPP with primary amphiphilicity (that is, amphiphilicity produced by the amino acid sequence itself, not caused by the folding structure), which includes a so-called "hydrophobic" domain rich in tryptophan, and one from SV40 ( Simian virus 40) the hydrophilic domain derived from the NLS (nuclear localization signal) of the large T antigen, and the spacer between them. The cysteamine group is present at the C-terminus. The presence of the cysteamine group at the C-terminus plays a crucial role in the efficiency of cargo entering the cell.
Henriques, S. et al. FEBS Letters Vol. 579, 4498 (2005).