Translocation of the pAntp peptide and its amphipathic analogue AP-2AL

The pAntp peptide, corresponding to the third helix of the homeodomain of t he Antennapedia protein, enters by a receptor-independent process into euka ryotic cells. The interaction between the pAntp peptide and the phospholipi d matrix of the plasma membrane seems to be the first step involved in the translocation mechanism. However, the mechanism by which the peptide transl ocates through the cell membrane is still not well established. We have inv estigated the translocation ability of pAntp through a protein-free phospho lipid membrane in comparison with a more amphipathic analogue. We show by f luorescence spectroscopy, circular dichroism, NMR spectroscopy, and molecul ar modeling that pAntp is not sufficiently helically amphipathic to cross a phospholipid membrane of a model system. Due to its primary sequence relat ed to its DNA binding ability in the Antennapedia homeodomain-DNA complex, the pAntp peptide does not belong to the amphipathic cr-helical peptide fam ily whose members are able to translocate by pore formation.