The cytotoxic plant protein, beta-purothionin, forms ion channels in lipidmembranes

Thionins are small cysteine-containing, amphipathic plant proteins found in seeds and vegetative tissues of a number of plant genera, Many of them hav e been shown to be toxic to microorganisms such as fungi, yeast, and bacter ia and also to mammalian cells. It has been suggested that thionins are pre sent in seeds to protect them, and the germinating seedling, from attack by phytopathogenic microorganisms, but the mechanism by which they kill cells remains unclear. Using electrophysiological measurements, we have shown th at beta-purothionin from wheat flour can form cation-selective ion channels in artificial lipid bilayer membranes and in the plasmalemma of rat hippoc ampal neurons. We suggest that the generalized toxicity of thionins is due to their ability to generate ion channels in cell membranes, resulting in t he dissipation of ion concentration gradients essential for the maintenance of cellular homeostasis.