Helicobacter pylori vacuolating toxin forms anion-selective channels in planar lipid bilayers: Possible implications for the mechanism of cellular vacuolation

The Helicobacter pylori VacA toxin plays a major role in the gastric pathol ogies associated with this bacterium. When added to cultured cells, VacA in duces vacuolation, an effect potentiated by preexposure of the toxin to low pH. Its mechanism of action is unknown. We report here that VacA forms ani on-selective, voltage-dependent pores in artificial membranes. Channel form ation was greatly potentiated by acidic conditions or by pretreatment of Va cA at low pH. No requirement for particular lipid(s) was identified. Select ivity studies showed that anion selectivity was maintained over the pH rang e 4.8-12, with the following permeability sequence: Cl- approximate to HCO3 - > pyruvate > gluconate > K+ approximate to Li+ approximate to Ba2+ > NH4. Membrane permeabilization was due to the incorporation of channels with a voltage-dependent conductance in the 10-30 pS range (2 M KCl), displaying a voltage-independent high open probability. Deletion of the NH2 terminus d omain (p37) or chemical modification of VacA by diethylpyrocarbonate inhibi ted both channel activity and vacuolation of HeLa cells without affecting t oxin internalization by the cells. Collectively, these observations strongl y suggest that VacA channel formation is needed to induce cellular vacuolat ion, possibly by inducing an osmotic imbalance of intracellular acidic comp artments.