Fusogenic properties of the ectodomains of hepatitis C virus envelope proteins.

We have used an isolated chimeric protein E1340 E2661 that includes the ectodomains of the envelope proteins of hepatitis C virus to study its interaction with model membranes. E1340 E2661 has some of the membrane destabilization properties, vesicle aggregation, lipid mixing and the release of internal aqueous content, which have previously been ascribed to fusion proteins. The effects are preferentially produced on vesicles of acidic phospholipids which would indicate the importance of the electrostatic interactions. In fact, an increase of the ionic strength of the buffer induced a considerable decrease of the destabilizing properties. Moreover, fluorescence polarization studies show that the recombinant protein reduces the amplitude of the thermal transition of dimyristoylphosphatidylglycerol vesicles and increases the transition temperature at pH 5.0 in a dose-dependent manner, indicating its insertion into the bilayer. Furthermore, a decrease of the pH induces a conformational change in the protein structure as evidenced by fluorescence of tryptophan residues and 4,4'-bis(1-anilinonaphthalene-8-sulfonate). A model for the fusion of hepatitis C virus with the host cell membrane can be postulated. The dissociation of E1E2 dimers would uncover the fusion peptides which can then interact with the polar lipid heads of the outer leaflet of the lipid bilayer and next insert into the hydrophobic moiety producing the destabilization of the bilayer which finally leads to fusion.