title: Cell-penetrating HIV1 TAT peptides float on model lipid bilayers.
abstract: Cell-penetrating peptides like the cationic HIV1 TAT peptide are able to translocate across cell membranes and to carry molecular cargoes into the cellular interior. For most of these peptides, the biophysical mechanism of the membrane translocation is still quite unknown. We analyzed HIV1 TAT peptide binding and mobility within biological model membranes. To this end, we generated neutral and anionic giant unilamellar vesicles (GUVs) containing DPPC, DOPC, and cholesterol and containing DPPC, DOPC, cholesterol, and DPPS (DOPS), respectively. First, we characterized the mobility of fluorescently labeled lipids (TR-DHPE) within liquid-ordered and liquid-disordered lipid phases by single-molecule tracking, yielding a D(LO) of 0.6 +/- 0.05 microm(2)/s and a D(LD) of 2.5 +/- 0.05 microm(2)/s, respectively, as a reference. Fluorescently labeled TAT peptides accumulated on neutral GUVs but bound very efficiently to anionic GUVs. Single-molecule tracking revealed that HIV1 TAT peptides move on neutral and anionic GUV surfaces with a D(N,TAT) of 5.3 +/- 0.2 microm(2)/s and a D(A,TAT) of 3.3 +/- 0.2 mum(2)/s, respectively. TAT peptide diffusion was faster than fluorescent lipid diffusion, and also independent of the phase state of the membrane. We concluded that TAT peptides are not incorporated into but rather floating on lipid bilayers, but they immerged deeper into the headgroup domain of anionic lipids. The diffusion constants were not dependent on the TAT concentration ranging from 150 pM to 2 microM, indicating that the peptides were not aggregated on the membrane and not forming any "carpet".
authors.affiliation: Institute for Physical and Theoretical Chemistry, Rheinische Friedrich-Wilhelms-University Bonn, Wegelerstrasse 12, D-53115 Bonn, Germany.
authors.forename: Corina
authors.initials: C
authors.lastname: Ciobanasu
authors.forename: Enno
authors.initials: E
authors.lastname: Harms
authors.forename: Gisela
authors.initials: G
authors.lastname: Tünnemann
authors.forename: M Cristina
authors.initials: MC
authors.lastname: Cardoso
authors.forename: Ulrich
authors.initials: U
authors.lastname: Kubitscheck
mesh_terms: D000838:Anions / Q000378:metabolism; D002412:Cations / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D015696:Gene Products, tat / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology; D015497:HIV-1 / Q000737:chemistry / Q000378:metabolism; D057927:Hydrophobic and Hydrophilic Interactions; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism*; D008954:Models, Biological; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology; D010539:Permeability; D010714:Phosphatidylethanolamines / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D055672:Static Electricity; D053835:Unilamellar Liposomes / Q000737:chemistry* / Q000378:metabolism*; D014783:Viscosity
chemical_list: D000838:Anions; D002412:Cations; D005456:Fluorescent Dyes; D015696:Gene Products, tat; D008051:Lipid Bilayers; D010455:Peptides; D010714:Phosphatidylethanolamines; D053835:Unilamellar Liposomes; C007510:1,2-dipalmitoyl-3-phosphatidylethanolamine