Beticolins, nonpeptidic, polycyclic molecules produced by the phytopathogenic fungus Cercospora beticola, as a new family of ion channel-forming toxins

Beticolins are toxins produced by Cercospora beticola, a phytopathogenic fu ngus responsible for the leaf spot disease of sugar beet. They form a famil y of 20 nonpeptidic compounds (named B0 to B19) that share the same polycyc lic skeleton but differ by isomeric configuration (ortho-or para-) and by a variable residue R (bridging two carbons in one of the six cycles). It has been previously shown that B0 assembles itself into a multimeric structure and forms ion channels into planar lipid bilayers (C. Goudet, A.-A. Very, M.-L. Milat, ICI. Ildefonse, J.-B. Thibaud, H. Sentenac, and J.-P. Blein, P lant J. 14:359-364, 1998). In the present work, we investigate pore formati on by three ortho-beticolins, B0, B2, and B4, and their related (i.e., same R) pam-isomers, B13, B1, and B3, respectively, using planar lipid bilayers . All beticolins were able to form ion channels with multiple conductance s tates, although the type of cyclization (ortho- or para-) and residue (R) r esult in variations of channel conductance and ionic permeability, respecti vely. Channel formation by beticolins is likely to be involved in the biolo gical activity of these toxins.