title: Translocation of a beta-peptide across cell membranes.
abstract: 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 beta-amino acid analogue of Tat 47-57 enters HeLa cells with comparable efficiency to Tat 47-57 itself (YGRKKRRQRRR). The beta-peptide is comprised of residues that bear the appropriate side chain at the beta-carbon. Both the alpha- and the beta-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 alpha-peptide abolished translocation activity, consistent with prior reports, and deletion of the three C-terminal beta3-homoarginine residues from the beta-peptide had a similarly adverse effect. Thus, alpha- and beta-peptide translocation processes show similar length/charge dependence. The beta-peptide appeared to be largely unfolded in water, which is consistent with the behavior of short Tat-derived alpha-peptides, but in methanol the beta-peptide adopted a helical conformation, in contrast to short Tat-derived alpha-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.
authors.affiliation: Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, USA.
authors.forename: Naoki
authors.initials: N
authors.lastname: Umezawa
authors.forename: Michael A
authors.initials: MA
authors.lastname: Gelman
authors.forename: Marcia C
authors.initials: MC
authors.lastname: Haigis
authors.forename: Ronald T
authors.initials: RT
authors.lastname: Raines
authors.forename: Samuel H
authors.initials: SH
authors.lastname: Gellman
mesh_terms: D002462:Cell Membrane / Q000378:metabolism; D015696:Gene Products, tat / Q000737:chemistry* / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D018613:Microscopy, Confocal; D009842:Oligopeptides / Q000737:chemistry* / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism*; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship
chemical_list: D015696:Gene Products, tat; D009842:Oligopeptides; D010446:Peptide Fragments