Phallolysin. A mushroom toxin, forms proton and voltage gated membrane channels

Phallolysin, a water soluble protein of Mr 34,000 produced by the poisonous mushroom Amanita phalloides, causes lysis of various mammalian cell types. Lysis is thought to be initiated by the formation of ion permeable membrane channels. We therefore studied the interaction of phallolysin with solvent-free planar lipid bilayers. In the presence of low phallolysin concentrations (10-100 nM) single channel current fluctuations were observed. Unit channel conductances are 44 pS in 500 mM NaCl and 77 pS in 1 M NaCl. Although the channel does not significantly discriminate between alkali cations, its permeability to Cl- is lower (PK+/PCl- = 4/1). Gating kinetics display a pronounced bursting behavior and a dependence on membrane voltage, cis side pH-value, and on membrane lipid composition. An equivalence relation between membrane voltage and proton concentration was found, i.e. a pH change of one unit is equivalent to a corresponding voltage change of 130 mV. Dependence on the amount of negatively charged lipids is explained by changes of the actual pH due to surface charge effects.