several antigenic peptide molecules, or multiple antigenic The interaction of the synthetic multiple antigenic peptide conpeptides (MAP), are more efficient immunogens (3,4), struct MAP 4 -VP1(11-25) with lipid membranes was studied by a partly because they confer some conformational stability to combination of spectroscopic and biophysical techniques. MAP 4the peptide antigens, which is important for inducing anti-VP1 showed an important surface activity when spread in an airbodies reactive with the native protein and partly because water interface, indicative of an amphipatic conformation. Since liposomes can allow a slow release of the antigen, resulting this peptide has a net anionic charge, we studied the degree of in continuous stimulation of the immune system (5). MAP 4interaction with model membranes of zwitterionic dipalmitoyl-VP1(11-25) is a tetrameric MAP with four repeats of the phosphatidylcholine (DPPC), anionic phosphatidylinositol (PI and DPPC/PI 9:1), or cationic stearylamine (SA and DPPC/SA epitope VP1(11-25) branched on a lysine residue core (2). 9:1). MAP 4 -VP1 was readily soluble in aqueous buffer, yet sponta-Immunogenicity can also be enhanced by administering the neously inserted from an aqueous subphase into cationic and zwitpeptides in association with carriers (6), such as proteins terionic monolayers up to limiting pressures of 20-30 mN/m. The (keyhole limpet hemacyanin, bovine seroalbumin), red induced surface pressure increases were in the order cationic ΓΊ blood cells, or liposomes. Liposomes exert an immunoadjuzwitterionic ΓΊ anionic monolayers. This indicates that the interacvant activity on associated protein (7, 8), enhancing both tion is mainly driven by electrostatic forces, although there is an humoral and cellular immune responses, thanks to an inimportant hydrophobic component, responsible for the penetration creased delivery of the antigen to antigen-presenting cells, in monolayers of neutral DPPC. Interaction of MAP 4 -VP1 with
and/or to a cytoplasmic delivery of the antigen, since it is unilamellar vesicles of DPPC, DPPC/SA (9:1), and DPPC/PI (9:1) labeled with 1,6-diphenyl-1,3,5-hexatriene (DPH) or with the current dogma that the antigen has to be produced inside 1-anilino-8-naphthalene sulfonic acid (ANS) was determined by the stimulator or target cell (9). Liposomes have been used changes in fluorescence polarization as a function of temperature. in association with inactivated HAV in a study where rapid Results showed that the presence of the positively charged SA in seroconversion, high level of mean antibody content, and the membrane strongly enhances the incorporation of MAP 4 -VP1 low reactogenicity were reported (10).
and that the peptide increases the fluidity of the bilayer and de-
In the present study, the interaction of MAP 4 -VP1(11creases the temperature of the phase transition.