C. Goudet et al., MAGNESIUM-IONS PROMOTE ASSEMBLY OF CHANNEL-LIKE STRUCTURES FROM BETICOLIN-0, A NONPEPTIDE FUNGAL TOXIN PURIFIED FROM CERCOSPORA-BETICOLA, Plant journal, 14(3), 1998, pp. 359-364
Beticolins are toxins produced by the fungus Cercospora beticola. Usin
g beticolin 0 (B0), we have produced a strong and Mg2+-dependent incre
ase in the membrane conductance of Arabidopsis protoplasts and Xenopus
oocytes. In protein-free artificial bilayers, discrete deflexions of
current were observed (12 pS unitary conductance in symmetrical 100 mM
KCl) in the presence of BO (approximately 10 mu M) and in the presenc
e of nominal Mg2+. Addition of 50 mu M Mg2+ induced a macroscopic curr
ent which could be reversed to single channel current by chelating Mg2
+ with EDTA. Both unitary and macroscopic currents were ohmic. The inc
rease in conductance of biological membranes triggered by BO is theref
ore likely to originate from the ability of this toxin to organize its
elf into transmembrane pores in the presence of Mg2+. The pore is poor
ly selective, displaying permeability ratios P-Cl/P-K, P-Na/P-K and P-
Ca/P-K close to 0.3, 0.65 and 0.4, respectively. Such channel-like act
ivity could be involved in the deleterious biological activity of the
toxin, by causing the collapse of ionic and electrical gradients throu
gh biological membranes together with Ca2+ influx and scrambling of ce
llular signals.