VacA from Helicobacter pylori: a hexameric chloride channel

FEBS Lett. 1999 Apr 30;450(1-2):101-4. doi: 10.1016/s0014-5793(99)00474-3.


VacA is a unique protein toxin secreted by the human pathogen Helicobacter pylori. At a neutral pH, the cytotoxin self-associates into predominantly dodecameric complexes. In this report, we show that at an acidic pH, VacA forms anion selective channels in planar phospholipid bilayers. Similar to several other chloride channels, the VacA channel exhibits a moderate selectivity for anions over cations (P(Cl):P(Na) = 4.2:1), inhibition by the blocker 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid and a permeability sequence, SCN- >> I- > Br- > Cl- > F, consistent with a 'weak field strength' binding site for the permeant anion. Single channel recordings reveal rapid transitions (486 s(-1)) between the closed state and a single open state of 24 pS (+60 mV, 1.5 M NaCl). Evaluation of the rate of increase in macroscopic current as well as atomic force microscopy suggest that this VacA channel is a hexamer, formed by the assembly of membrane-bound monomers. Not only are these VacA channels likely to play an important role in the pathological activity of this toxin, but they may also serve as a model system to further investigate the mechanism of anion selectivity in general.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / pharmacology
  • Anions
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / ultrastructure
  • Bacterial Toxins / chemistry*
  • Chloride Channels / chemistry*
  • Chloride Channels / ultrastructure
  • Electrophysiology
  • Helicobacter pylori / chemistry*
  • Hydrogen-Ion Concentration
  • Liposomes
  • Microscopy, Atomic Force
  • Protein Conformation


  • Anions
  • Bacterial Proteins
  • Bacterial Toxins
  • Chloride Channels
  • Liposomes
  • VacA protein, Helicobacter pylori
  • 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid