Abstract
The third helix of the homeodomain of the Antennapedia homeoprotein can translocate through the cell membrane into the nucleus and can be used as an intracellular vehicle for the delivery of oligopeptides and oligonucleotides. A 16‐amino acid‐long peptide fragment, called penetratin, is internalized by the cells in a specific, non‐receptor‐mediated manner. For a better understanding of the mechanism of the transfer, penetratin and two analogs were synthesized:
(1) penetratin
RQIKIWFQNRRMKWKK (peptide 1);
(2) (6,14‐Phe)‐penetratin,
RQIKIFFQNRRMKFKK (peptide 2);
(3) dodecapeptide,
RQIKIWF‐R‐KWKK (peptide 3);
The conformation of penetratin peptides 1–3 was examined in both extracellular matrix‐mimetic and membrane‐mimetic environments. ^1^H‐NMR and CD spectroscopic measurements were performed in mixtures of TFE/water with different ratios. Peptides 1–3 were labeled by reacting their N‐terminal free amino group with fluorescein isothiocyanate (FITC). Membrane translocation of the labelled peptides was studied with cell cultures [WEHI 164 murine fibrosarcoma cells (WC/1); chicken fibroblast cells (CEC‐32); chicken monocytic cells (HD‐11); human fibroblast (SV 80) and human monocytic cells (MonoMac‐6)]. Confocal laser scanning microscopy and flow cytometry assay were used to study membrane translocation. Amphiphilicity was calculated for each peptide. In our experiments all the penetratin peptides penetrated into the cells. Helical conformation and membrane translocation ability showed little correlation: substitution of the two Trp with Phe increased the stability of helical conformation but decreased membrane translocation activity. The results of fluorescence microscopy and flow cytometry show that penetratin can be translocated into the cells by two mechanisms: endocytosis and direct transport through the cell membrane. Copyright © 2003 John Wiley & Sons, Ltd.