Cellular internalization of a cargo complex with a novel peptide derived from the third helix of the islet-1 homeodomain. Comparison with the penetratin peptide

Cellular translocation into a human Bowes melanoma cell line was investigat ed and compared for penetratin and pIsl, two peptides that correspond to th e third helices of the related homeodomains, from the Antennapedia transcri ption factor of Drosophila and the rat insulin-1 gene enhancer protein, res pectively. Both biotinylated peptides internalized into the cells with simi lar efficacy, yielding an analogous intracellular distribution. When a larg e cargo protein, 63 kDa avidin, was coupled to either peptide, efficient ce llular uptake for both the peptide-protein complexes was observed. The inte ractions between each peptide and SDS micelles were studied by fluorescence spectroscopy and acrylamide quenching of the intrinsic tryptophan (Trp) fl uorescence. Both peptides interacted strongly and almost identically with t he membrane mimicking environment. Compared to penetratin, the new transpor t peptide pIsl has only one Trp residue, which simplifies the interpretatio n of the fluorescence spectra and in addition has a native Cys residue, whi ch may be used for alternative coupling reactions of cargoes of different c haracter.