A Single Hydrophobic Residue Enhances the Uptake of Short Cationic Proline-Rich Cell-Penetrating Peptides

Cationic cell-penetrating peptides (CPPs) are a versatile platform for intracellular cargo delivery into mammalian cells but often suffer from low cellular uptake and endosomal entrapment. Here, we investigated the effect of a single cyclohexylalanine (Cha) residue at the termini of short, conformationally constrained cationic peptides composed of (4S)-guanidiniumproline (Gup). We show that this hydrophobic residue promotes internalization. Our studies also revealed that a hydrophobic residue positioned at the C-terminus enhances cellular uptake more than when at the N-terminus. Comparative studies at different temperatures are consistent with a major entry pathway via direct translocation across the plasma membrane. The findings are useful for the design of CPPs, particularly for enhancing the cellular translocation of otherwise weakly cell-penetrating peptides.