title: Conformation and orientation of penetratin in phospholipid membranes.
abstract: The binding, conformation and orientation of a hydrophilic vector peptide penetratin in lipid membranes and its state of self-association in solution were examined using circular dichroism (CD), analytical ultracentrifugation and fluorescence spectroscopy. In aqueous solution, penetratin exhibited a low helicity and sedimented as a monomer in the concentration range approximately 50-500 microM. The partitioning of penetratin into phospholipid vesicles was determined using tryptophan fluorescence anisotropy titrations. The apparent penetratin affinity for 20% phosphatidylserine/80% egg phosphatidylcholine vesicles was inversely related to the total peptide concentration implying repulsive peptide-peptide interactions on the lipid surface. The circular dichroism spectra of the peptide when bound to unaligned 20% phosphatidylserine/80% egg phosphatidylcholine vesicles and aligned hydrated phospholipid multilayers were attributed to the presence of both alpha-helical and beta-turn structures. The orientation of the secondary structural elements was determined using oriented circular dichroism spectroscopy. From the known circular dichroism tensor components of the alpha-helix, it can be concluded that the orientation of the helical structures is predominantly perpendicular to the membrane surface, while that of the beta-type carbonyls is parallel to the membrane surface. On the basis of our observations, we propose a novel model for penetratin translocation.
authors.affiliation: Russell Grimwade School of Biochemistry and Molecular Biology, University of Melbourne, 3010, Victoria, Australia. andrew.clayton@ludwig.edu.au
authors.forename: A H A
authors.initials: AH
authors.lastname: Clayton
authors.forename: B W
authors.initials: BW
authors.lastname: Atcliffe
authors.forename: G J
authors.initials: GJ
authors.lastname: Howlett
authors.forename: W H
authors.initials: WH
authors.lastname: Sawyer
mesh_terms: D002352:Carrier Proteins / Q000737:chemistry*; D057846:Cell-Penetrating Peptides; D008567:Membranes, Artificial; D010743:Phospholipids / Q000737:chemistry*; D011487:Protein Conformation
chemical_list: D002352:Carrier Proteins; D057846:Cell-Penetrating Peptides; D008567:Membranes, Artificial; D010743:Phospholipids; C414409:penetratin