title: Cluster organization and pore structure of ion channels formed by beticolin 3, a nonpeptidic fungal toxin.
abstract: Beticolin 3 (B3) belongs to a family of nonpeptidic phytotoxins produced by the fungus Cercospora beticola, which present a broad spectrum of cytotoxic effects. We report here that, at cytotoxic concentration (10 microM), B3 formed voltage-independent, weakly selective ion channels with multiple conductance levels in planar lipid bilayers. In symmetrical standard solutions, conductance values of the first levels were, respectively, 16 +/- 1 pS, 32 +/- 2 pS, and 57 +/- 2 pS (n = 4) and so on, any conductance level being roughly twice the lower one. Whether a cluster organization of elementary channels or different channel structures underlies this particular property was addressed by investigating the ionic selectivity and the pore size corresponding to the first three conductance levels. Both selectivity and pore size were found to be almost independent of the conductance level. This indicated that multiple conductance behavior resulted from a cluster organization of "B3 elementary channels." According to the estimated pore size and analyses of x-ray diffraction of B3 microcrystals, a structural model for "B3 elementary channels" is proposed. The ability to form channels is likely to be involved in the biological activity of beticolins.
authors.affiliation: Laboratoire de Biochimie et Physiologie Moléculaire des Plantes, CNRS URA 2133/ENSA-M/INRA/UM2, 34060 Montpellier 1, France.
authors.forename: C
authors.initials: C
authors.lastname: Goudet
authors.forename: J P
authors.initials: JP
authors.lastname: Benitah
authors.forename: M L
authors.initials: ML
authors.lastname: Milat
authors.forename: H
authors.initials: H
authors.lastname: Sentenac
authors.forename: J B
authors.initials: JB
authors.lastname: Thibaud
mesh_terms: D055592:Biophysical Phenomena; D001703:Biophysics; D004553:Electric Conductivity; D006576:Heterocyclic Compounds, 4 or More Rings; D066298:In Vitro Techniques; D007473:Ion Channels / Q000737:chemistry* / Q000187:drug effects; D008051:Lipid Bilayers; D008564:Membrane Potentials; D008958:Models, Molecular; D008968:Molecular Conformation; D009183:Mycotoxins / Q000737:chemistry* / Q000633:toxicity
chemical_list: D006576:Heterocyclic Compounds, 4 or More Rings; D007473:Ion Channels; D008051:Lipid Bilayers; D009183:Mycotoxins; C403640:beticolin 3