Analysis of the effect of a peptide sequence of the E2 protein (HGV/GBV-C) on the physicochemical properties of zwitterionic and negatively charged bilayers.

The membrane-interacting properties of a potential epitope of GB virus C/hepatitis G virus located at the region (99-118) of the E2 structural protein were investigated using several fluorescence techniques. SUV of DMPC:DPPC (1:1) or DMPG:DPPC (1:1) zwitterionic and anionic mixtures, respectively, were used as model membranes. FRET with NBD-PE as energy donor and Rho-PE as energy acceptor-labelled SUV indicated that the peptide was able to fuse both zwitterionic and anionic SUVs, the latter requiring lower peptide concentrations. However, the peptide increased the steady-state anisotropy of DPH embedded in the hydrophobic centre of the membrane with zwitterionic headgroups and to a lesser extent in anionic bilayers, suggesting that charge-charge interactions are not required for membrane interactions and also confirming the FRET results. No changes in anisotropy were observed with the probe TMA-DPH located at the surface of the bilayer. Finally, analysis of the intrinsic emission fluorescence of the tryptophan residue, upon incubation with SUV, showed a blue shift in the presence of anionic bilayers, both below and above the main transition temperature (T(m)) (gel to liquid-crystalline state) and, to a lesser extent, with the zwitterionic model membrane.