Internalization of cationic peptides: the road less (or more?) traveled

Facilitating the entry of molecules into mammalian cells is of great interest to fields as diverse as cell biology and drug delivery. The discovery of natural protein transduction domains and the development of artificial ones, including polyarginine, provides a means to achieve this goal. Here, we comment on key chemical and biological aspects of cationic peptide internalization, including the physiological relevance of this process.