Describing how peptides and proteins traverse cell membranes is huge in the field of cell biology. Peptides, short chains of amino acids, could one day be used as molecular ferries transporting therapeutic genes or proteins across lipid bilayers and directly into the cytosol, where many crucial biochemical pathways start. But the journey from outside a cell to the cytoplasm is no small feat for bulky peptides—researchers have been trying to map the various routes for decades.
Since the early 1990s, researchers studying how cell-penetrating peptides, which include some transcription factors and parts of viruses, gain access to the inside of cells have focused on different modes of endocytosis—where cells encapsulate extracellular material in membrane-bound vesicles and import them. Several flavors of endocytosis exist, from macropinocytosis, where cells gulp in large amounts of extracellular fluid containing macromolecules in solution, to uptake mediated by membrane proteins or lipids.
In 2007, a paper ...
