Translocation of a β-peptide across cell membranes

Short cationic peptides derived from DNA-binding proteins, of which HIV Tat is a prototype, can cross the membranes of living cells, and they can bring covalently attached moieties (proteins, drugs) along with them. We show that a β-amino acid analogue of Tat 47-57 enters HeLa cells with comparable efficiency to Tat 47-57 itself (YGRKKRRQRRR). The β-peptide is comprised of residues that bear the appropriate side chain at the β-carbon. Both the α- and the β-peptide were conjugated to fluorescein at the N terminus, and cell penetration was monitored by confocal fluorescence microscopy. Deletion of the three C-terminal arginine residues from the α-peptide abolished translocation activity, consistent with prior reports, and deletion of the three C-terminal β3-homoarginine residues from the β-peptide had a similarly adverse effect. Thus, α- and β-peptide translocation processes show similar length/charge dependence. The β-peptide appeared to be largely unfolded in water, which is consistent with the behavior of short Tat-derived α-peptides, but in methanol the β-peptide adopted a helical conformation, in contrast to short Tat-derived α-peptides. Our results show that neither altering the oligomeric backbone (amide group spacing) nor increasing the intrinsic propensity to adopt a specific secondary structure affects translocation activity. Copyright © 2002 American Chemical Society.