The membrane-interacting properties of two potential epitopes of the GB virus C/Hepatitis G virus, located respectively at the regions (99-118) of the E2 structural protein and (440-460) of the NS3 non-structural protein were studied. Changes in the intrinsic fluorescence of Trp and Tyr residues after the addition of DPPC-LUV revealed that the peptide-membrane interaction was optimal above the gel-liquid crystalline transition temperature of the lipid. Differential scanning calorimetry studies showed that the E2 peptide incorporated into lipid bilayers perturbs the packing of lipids and affects their thermotropic properties. Moreover, the 20-mer structural peptide induced a slow leakage of vesicular contents at 55 degrees C.