Fluorescence study on the interaction of a multiple antigenic peptide fromhepatitis A virus with lipid vesicles

The interaction of the multiple antigenic peptide MAP(4)VP3 with lipid memb ranes has been studied by spectroscopic techniques. MAP(4)VP3 is a multimer ic peptide that corresponds to four units of the sequence 110-121 of the ca psid protein VP3 of hepatitis A virus. In order to evaluate the electrostat ic and hydrophobic components on the lipid-peptide interaction small unilam elar vesicles of different compositions, including zwitterionic dipalmitoyl phosphatidylcholine (DPPC), anionic dipalmitoylphosphatidylcholine/phosphat idylinositol (DPPC : PI 9:1), and cat ionic dipalmitoylphosphatidylcholine/ stearylamine (DPPC: SA 9.5:0.5), were used as membrane models. Intrinsic tr yptophan fluorescence changes and energy transfer experiments show that MAP (4)VP3 binds to all thr ee types of vesicles with the same stoichiometry in dicating that the electrostatic component of the interaction is nor importa nt lar binding of this anionic peptide. Steady-state polarization experimen ts with vesicles labeled with 1,6-diphenyl-1,3,5-hexatriene or with 1-anili no-8-naphtalene sulphonic acid indicate that MAP(4)VP3 induces a change in the packing of the bilayers, with a decrease in the fluidity of the lipids and an increase in the temperature of phase transition in all the vesicles. The percentage of lipid exposed to the bulk aqueous phase is around 60% in intact vesicles, and it does not change upon binding of MAP(4)VP3 to DPPC vesicles, indicating that the peptide does not alter the permeability of th e membrane. An increase in the amount of lipid exposed to the aqueous phase iii cationic vesicles indicates either lipid flip-flop or disruption of th e vesicles. Binding to DPPC vesicles occurs without leakage of entrapped ca rboxy-fluorescein, even at high mol functions of peptide. However, a time-d ependent leakage is seen with cationic DPPC/SA and anionic DPPC/PI vesicles , indicating that the peptide induces membrane destabilization and not lipi d flip-flop. Resonance energy transfer experiments show that MAP(4)VP3 leak age from cationic vesicles is due to membrane fusion, whereas leakage from anionic vesicles is nor accompanied by lipid mixing. Results show that MAP( 4)VP3 interacts strongly with the liquid components of the membrane, and al though binding is not of electrostatic nature, the bound form of the peptid e has different activity depending on the membrane net charge; thus, it is membrane disruptive in cationic and anionic vesicles, whereas no destabiliz ing effect is seen in DPPC vesicles. (C) 2000 John Wiley & Sons, Inc.