The acid activation of Helicobacter pylori toxin VacA: structural and membrane binding studies.
The cell vacuolating activity of the protein toxin VacA, released by Helicobacter pylori, is strongly increased in vitro by exposure to acidic pH followed by neutralization. This short acid exposure does not increase significantly the binding of VacA to cell or to lipid membranes. However, membrane photolabeling with photoactivatable radioactive phospholipids and ANS binding studies show that VacA transiently exposed to pH equal or lower than 5 changes conformation and exposes on its surface hydrophobic segments. Both the 32 and the 58 kDa subunits of the toxin insert in the lipid bilayer and interact with the fatty acid chains of phospholipids. Membrane binding and penetration are enhanced by incubating target cells or liposomes with the toxin at mild acidic pH values, similar to those present around H. pylori on the stomach mucosa. These findings are discussed with respect to the critical step in cell intoxication consisting in the translocation of the active toxin domain into the cell cytosol. We suggest that membrane translocation takes place at the plasma membrane level.
Centro Consiglio Nazionale delle Ricerche su Biomembrane and Dipartimento di Scienze Biomediche, Università di Padova, Via G. Colombo 3, Padova, I-35100, Italy.
M
M
Molinari
C
C
Galli
M
M
de Bernard
N
N
Norais
J M
JM
Ruysschaert
R
R
Rappuoli
C
C
Montecucco
D000345:Affinity Labels; D000817:Anilino Naphthalenesulfonates / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D001427:Bacterial Toxins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D005753:Gastric Mucosa / Q000378:metabolism; D016480:Helicobacter pylori / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers / Q000378:metabolism; D008081:Liposomes / Q000378:metabolism; D015394:Molecular Structure; D010743:Phospholipids / Q000737:chemistry; D011485:Protein Binding / Q000502:physiology; D011487:Protein Conformation
D000345:Affinity Labels; D000817:Anilino Naphthalenesulfonates; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D008081:Liposomes; D010743:Phospholipids; C074689:VacA protein, Helicobacter pylori; C027132:1-anilino-8-naphthalenesulfonate