Quantitative analysis of the binding of melittin to planar lipid bilayers allowing for the discrete-charge effect |
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Authors: | Peter Schoch David F. Sargent |
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Affiliation: | Institut für Molekularbiologie und Biophysik, Eidgenössische Technische Hochschule, CH-8093 Zürich Switzerland |
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Abstract: | The interaction of melittin with lecithin bilayers was studied using the resulting surface potentials at the bilayer/water interfaces to monitor the association. Melittin added to the aqueous phase binds strongly to the interface but remains localized on that side of the bilayer to which it is added. The analysis of the binding curves reveals the inadequacy of the Gouy-Chapman theory for the fixed-charge surface potential in describing the electrostatic potential experienced by the adsorbed molecules. Calculations based on the Stern equation, modified for a discrete charge distribution, give a good fit to the experimental data. The thermodynamic analysis revealed different binding energies, Δ°, at 10 and 100 mM ionic strength (?7.85 and ?8.26 kcal/mol, respectively). Binding saturates at an area of 650 Å2 per melittin molecule. A change in the surface dipole potential corresponding to ?1.1 debye/?a () had to be postulated. The Debye-Hückel length for a charge bound to the membrane/solution interface was found to be about one-third smaller than in bulk solution. |
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Keywords: | Melittin Lipid-protein interaction Binding parameter Surface potential Discrete-charge effect (Bilayer) |
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