Interfacial Properties of a Synthetic Peptide Derived from Hepatitis G Virus E2 Protein: Interaction with Lipid Monolayers Jorge Casas, †,‡ Marta Espina, † Marta Haro, § Felix Royo, § M. Asuncio ´n Alsina, † Isabel Haro, ‡ and Concepcio ´n Mestres* ,† CSIC Associate Unity “Peptides & Proteins: Physicochemical Studies”, Physicochemistry Department, Faculty of Pharmacy, AV. Joan XXIII s.n., 08028 Barcelona, Spain, Department of Peptide & Protein Chemistry, IIQAB-CSIC, Jordi Girona Salgado 18-26, 08034 Barcelona, Spain, and Department of Organic Chemistry and Physicochemisty, Faculty of Sciences, Ciudad UniVersitaria, P. San Francisco s.n., 50009 Zaragoza, Spain ReceiVed July 6, 2005. In Final Form: September 13, 2005 A useful approach to get information about the potential fusogenic ability of virus synthetic peptides is the study of its interfacial properties and subsequent study in mono- and bilayers. In this work, we have characterized by means of physicochemical tools (i.e. compression isotherms and surface activity) the sequence 267-284, LLGTEVSEV- LGGAGLTGG, derived from the E2 structural protein of HGV/GBV-C. The adsorption of the peptide at the air/water interface was monitored by following the increase in surface pressure as a function of time at two different pH values: 5 and 7. Parameters such as surface excess or molecular area were calculated from the equation of Gibbs. The peptide showed a tendency to migrate to the surface of a saline-buffered solution. It formed stable monolayers at the air/water interface giving a compression isotherm with a shape consistent with that of some R-helical peptide conformations. Brewster angle microscopy (BAM) showed that through compression the peptide formed multilayers. The studies with lipid monolayers (DPMC, DMPC/DMPG, and DMPC/DMTAP) showed that the peptide interacts with all the lipids assayed producing a marked disrupting effect upon them. In these effects electrostatic interactions seem to have some participation. Introduction Hepatitis G virus (HGV) and GB virus C (GBV-C) are two isolates of the same virus independently discovered. 1 Although hepatitis G virus (HGV/GBV-C) infection is common and frequently persists in humans, this infection has not been found to be associated with any known disease state. Nevertheless, its importance has increased since recent studies have suggested that HGV/GBV-C infection in HIV-positive people is associated with prolonged survival and in vitro coinfection of human lymphocytes leads to decreased HIV replication. 2 On the basis of the genome organization and sequence homology, HGV/ GBV-C is the most closely related human virus to hepatitis C virus (HCV) and it has also been classified as a member of the Flaviviridae. Like HCV, it has a single-stranded RNA genome of approximately 9400 nucleotides long, but the mode of viral replication of HGV/GBV-C has not been yet elucidated. Fusion events are associated with the entry of enveloped viruses into host cells. Through this process the virus can insert its genome into the cellular cytoplasm and carry out subsequent infective events. 3 The fusion peptides operate at the interface between the extracellular medium and the membrane surface of the host cell, an environment well mimicked by the air/water interface. Thus, the comprehension of the interfacial properties of peptides belonging to relevant viral protein domains is important to gain insights into the infection and proliferation of viruses. In this study, a putative fusion peptide located in the structural protein E2, LLGTEVSEVLGGAGLTGG (M r ) 1629.9), was selected by computer-aided prediction algorithms based on scales developed by Wimley and White, 4 Chou and Fasman, 5 and Kyte and Dolittle 6 and afterward characterized by means of physi- cochemical tools. To have more insight into the conformational behavior at the air/water interface and its intermolecular interactions, we have chosen to use the monolayers technique. 7 This information is of capital importance for further studies about the fusogenicity of the peptide in lipid mono- and bilayers. 8 The physicochemical analysis combined with Brewster angle mi- croscopic visualization of the interface allows us then to discuss the properties of the peptide at the air/water interface and its interaction with lipids. In this work we have studied the effect of E2(267-284) peptide with a zwitterionic phospholipid, DMPC (dimyristoylphosphatidylcholine), and the influence of anionic and cationic lipids. DMPG (dimyristoylphosphatidylglycine) and DMTAP (dimyristoyltrimethylammonium propane), on this interaction. Even though DMTAP is not present in biological membranes, we have chosen it, as other authors, 9 to better understand the role of the lipid charge in the interaction. Materials and Methods Chemicals. Ultrapure water was produced by deionization and Nanopure purification coupled to a Milli-Q purification system (Milli-Q system, Millipore Corp.) up to a resistivity of 18.2 MΩ cm. Chloroform and acetonitrile proanalysis were from Merck (Poole, Dorset, U.K.). * Corresponding author. Tel: +34934024553. Fax: +34934035987. E-mail: cmestresm@ub.edu. † Faculty of Pharmacy. ‡ Department of Peptide & Protein Chemistry. § Ciudad Universitaria. (1) Halasz, R.; Weiland, O.; Sa ¨llberg, M. Scand. J. Infect. Dis. 2001, 33, 572-580. (2) Stapleton, J. T. Semin. LiVer Dis. 2003, 23 (2), 137-148. (3) White, J. Science 1992, 258, 917-924. (4) Wimley, S. H.; White W. C. Nat. Struct. Biol. 1996, 3 (10), 842-848. (5) Chou, P. Y.; Fasman, G.D. AdV. Enzymol. Relat. Areas Mol. Biol. 1978, 47, 45-148. (6) Kyte, J.; Doolittle, R. F. J. Mol. Biol. 1982, 157, 105-132. (7) Turnois, H.; Fieles, P.; Demel, R.; de Gier, J.; de Kruijff. B. Biophys. J. 1989, 55, 557-569. (8) Tommerhauser, D.; Galla, H. Chem. Phys. Lipids 1998, 94, 81-96. (9) Ege, C.; Lee, K. Y. C. Biophys. J. 2004, 87, 1732-1740. 246 Langmuir 2006, 22, 246-254 10.1021/la051812h CCC: $33.50 © 2006 American Chemical Society Published on Web 12/03/2005