Interaction of GB Virus C/Hepatitis G Virus Synthetic Peptides with Lipid Langmuir Monolayers and Large Unilamellar Vesicles

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Abstract
In this paper, we aimed to continue the previous study undertaken with one segment of El protein belonging to the GB virus C/hepatitis G virus (GBV-C/HGV), specifically between the 53-66 amino acids and their palmitoyl derivative peptide. The sequence selection has been made on the basis of different prediction algorithms of hydrophobicity and antigenicity. Their interactions between two different in vitro membrane models, lipid Langmuir monolayers and vesicles of different lipidic composition, have been evaluated. For this purpose., different lipids, varying the charge and the unsaturations of the hydrocarbon chain 1,2-dipahnitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-dipalmitoylsn-glycero-3-[phospho-rac-(1-glycerol)] (sodium salt) (DPPG) and 1,2-dioleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (sodium salt) (DOPG), have been selected. Miscibility and peptides/lipids interactions have been analyzed on the basis of surface pressure (pi)-mean molecular area (A) isotherms, which have been recorded for pure and mixed monolayers of different composition spread at the air/water interface. Furthermore, E1(53-66) sequence and PalmE1(53-66) have been labeled with a fluorescent group, succinimidyl 6-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)hexanoate (NBD succinimide), in order to study their behavior in the presence of vesicles. The obtained results are consistent with the existence of electrostatic (attractive) intermolecular interactions between the two positive net charges of the peptides and the polar heads of negative-charged lipids. However, both the lipidic membrane fluidity and the palmitic chain linked to the native peptide play an important role in the balance between the electrostatic forces established at the interface and the hydrophobic ones established inside the membrane. The fluorescence assays have demonstrated that electrostatic forces clearly predominate over the hydrophobic interactions only when the native sequence is retained at the polar interface of DPPG and DOPG vesicles. However, the palmitic tail linked to the peptide helped its penetration in the hydrophobic environment of the membrane, and this process was favored by decreasing the membrane fluidity.