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Biophys J, March 1999, p. 1401-1409, Vol. 76, No. 3
*Centro CNR per lo Studio delle Biomembrane and Dipartimento di Scienze Biomediche, Università di Padova, Padova, Italy, and #Centro di Ricerche I.R.I.S., CHIRON S.p.a., Siena, Italy
The Helicobacter pylori VacA toxin plays a
major role in the gastric pathologies associated with this bacterium.
When added to cultured cells, VacA induces vacuolation, an effect
potentiated by preexposure of the toxin to low pH. Its mechanism of
action is unknown. We report here that VacA forms anion-selective,
voltage-dependent pores in artificial membranes. Channel formation was
greatly potentiated by acidic conditions or by pretreatment of VacA at
low pH. No requirement for particular lipid(s) was identified.
Selectivity studies showed that anion selectivity was maintained over
the pH range 4.8-12, with the following permeability sequence:
Cl
HCO3
> pyruvate > gluconate > K+
Li+
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 domain (p37) or chemical modification of VacA
by diethylpyrocarbonate inhibited both channel activity and vacuolation
of HeLa cells without affecting toxin internalization by the cells.
Collectively, these observations strongly suggest that VacA channel
formation is needed to induce cellular vacuolation, possibly by
inducing an osmotic imbalance of intracellular acidic compartments.
Biophys J, March 1999, p. 1401-1409, Vol. 76, No. 3
© 1999 by the Biophysical Society 0006-3495/99/03/1401/09 $2.00
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