Open AccessLipid Interaction of the 37‐kDa and 58‐kDa Fragments of the Helicobacter Pylori Cytotoxin
Author(s) -
Moll Gert,
Papini Emanuele,
Colonna Raffaele,
Burroni Daniela,
Telford John,
Rappuoli Rino,
Montecucco Cesare
Publication year - 1995
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1995.947_a.x
Subject(s) - liposome , cytosol , biochemistry , chemistry , vesicle , toxin , lipid bilayer , biophysics , lipid bilayer fusion , intracellular , tryptophan , membrane , biology , amino acid , enzyme
Helicobacter pylori cytotoxin vacA (95 kDa) causes a vacuolar degeneration of epithelial cells. There is evidence that this protein toxin acts inside cells, and hence has to cross a cell membrane. This cytotoxin is frequently obtained as two fragments of 58 kDa (p58) and 37 kDa (p37) and it is available only in minute amounts. Here, its membrane interaction was studied with the two fragments, produced in Escherichia coli. Light scattering and energy transfer experiments show that p37 and p38 cause aggregation and fusion of small unilamellar lipid vesicles: only a reversible aggregation is induced at neutral pH, whereas at acid pH fusion also takes place. p58, but not p37, causes potassium efflux from liposomes and this occurs only at acid pH. Hydrophobic photolabelling with photoactivatable phosphatidylcholines inserted into liposomes shows that both fragments are labelled at neutral pH. The amount of labelling of the two fragments is much higher at acid pH, consistent with a further penetration into the hydrophobic core of the lipid bilayer. Tryptophan fluorescence measurements indicate that the two fragments undergo a pH‐driven conformational change. These data are consistent with cytotoxin entry in the cell cytosol via an intracellular acidic compartment.