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VacA from Helicobacter pylori: a hexameric chloride channel
H Iwamoto1, D M Czajkowsky, T L Cover
1Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville 22908, USA.
FEBS Letters
|June 1, 1999
Summary
The VacA toxin from Helicobacter pylori forms anion-selective channels at acidic pH. These channels, likely hexamers, exhibit moderate anion selectivity and may contribute to the pathogen's harmful effects.
Area of Science:
- Microbiology
- Biophysics
- Molecular Biology
Background:
- Helicobacter pylori is a human pathogen that secretes the unique protein toxin VacA.
- At neutral pH, VacA forms dodecameric complexes.
- The function and structure of VacA at acidic pH remain incompletely understood.
Purpose of the Study:
- To investigate the channel-forming properties of VacA at acidic pH.
- To characterize the ion selectivity and conductance of VacA channels.
- To determine the oligomeric state and assembly of VacA in membranes.
Main Methods:
- Planar phospholipid bilayer reconstitution assays.
- Single-channel and macroscopic current recordings.
- Inhibition studies with 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid.
- Atomic force microscopy.
Main Results:
- VacA forms anion-selective channels in planar phospholipid bilayers at acidic pH.
- The VacA channel shows moderate anion selectivity (P(Cl):P(Na) = 4.2:1) and a permeability sequence consistent with a 'weak field strength' binding site.
- Single-channel recordings indicate rapid gating between closed and open states (24 pS conductance).
- Evidence suggests VacA channels are hexamers formed by membrane-bound monomers.
Conclusions:
- VacA forms functional anion-selective channels at acidic pH, likely hexameric structures.
- These VacA channels are implicated in the pathological activity of Helicobacter pylori.
- The VacA channel serves as a valuable model for studying anion selectivity mechanisms.