title: Modes of membrane interaction of a natural cysteine-rich peptide: viscotoxin A3.
abstract: Among the very homologous family of alpha- and beta-thionins, known for their antimicrobial activity, the viscotoxin subfamily differs from other members because it is cytotoxic against tumoral cells but weakly hemolytic. We studied the interactions between the most active of these toxins, viscotoxin A3 (VA3), and model membranes made of phosphatidylcholine and phosphatidylserine (PS), the major zwitterionic and acidic phospholipids found in eukaryotic cells. Monolayer studies showed that electrostatic forces are essential for the interaction and are mainly involved in modulating the embedding of the toxin in the PS head group region. This in turn induces membrane stiffening, as shown by fluorescence polarization assays with 1,6-diphenyl-1,3,5-hexatriene and its derivatives. Moreover, vesicle permeabilization analyses showed that there are two modes of interaction, which are directly related to the stiffening effect and depend on the amount of VA3 bound to the surface of the vesicles. We propose an interaction model in which the embedding of VA3 in the membrane induces membrane defects leading to the gradual release of encapsulated dye. When the surfaces of the vesicles are saturated with the viscotoxin, complete vesicle destabilization is induced which leads to bilayer disruption, all-or-none encapsulated dye release and rearrangement of the vesicles.
authors.affiliation: Institut de Pharmacologie et de Biologie Structurale, UMR-CNRS 5089, Toulouse Cedex 4, France. andre.lopez@ipbs.fr
authors.forename: Alexandre
authors.initials: A
authors.lastname: Coulon
authors.forename: Emir
authors.initials: E
authors.lastname: Berkane
authors.forename: Anne Marie
authors.initials: AM
authors.lastname: Sautereau
authors.forename: Konrad
authors.initials: K
authors.lastname: Urech
authors.forename: Pierre
authors.initials: P
authors.lastname: Rouge
authors.forename: Andre
authors.initials: A
authors.lastname: Lopez
mesh_terms: D002462:Cell Membrane / Q000737:chemistry* / Q000187:drug effects; D002463:Cell Membrane Permeability; D004161:Diphenylhexatriene; D005452:Fluoresceins; D005454:Fluorescence Polarization; D005456:Fluorescent Dyes; D008051:Lipid Bilayers / Q000737:chemistry; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; D028321:Plant Preparations; D010940:Plant Proteins; D011485:Protein Binding; D054790:Ribosome Inactivating Proteins, Type 2; D055672:Static Electricity; D014118:Toxins, Biological / Q000737:chemistry* / Q000494:pharmacology
chemical_list: D005452:Fluoresceins; D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; D028321:Plant Preparations; D010940:Plant Proteins; D054790:Ribosome Inactivating Proteins, Type 2; D014118:Toxins, Biological; C009674:ribosome inactivating protein, Viscum; D004161:Diphenylhexatriene; C045132:4-carboxyfluorescein; C488038:viscotoxin