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Negatively cooperative binding of melittin to neutral phospholipid vesicles
* 1 , 2, 3
1  Institut Universitari de Ciència Molecular, Universitat de València, Edifici d'Instituts de Paterna, P. O. Box 22085, E-46071 València, Spain
2  Departamento de Química, Universidad Politécnica de Valencia, Camino de Vera s/n, E-46022 València, Spain
3  Departamento de Ciencias Experimentales, Facultad de Ciencias Experimentales, Universidad Católica de Valencia San Vicente Mártir, Guillem de Castro-94, E-46003 València, Spain

Abstract: The association of basic amphipathic peptides to neutral phospholipid membranes is investigated in terms of binding and partition models. The binding of native and modified melittin to egg-yolk phosphatidylcholine vesicles is studied by steady-state fluorescence spectroscopy. The effect of the ionic strength shows an enhancement of the association as the ionic strength increases. After correction for electrostatic effects by the Gouy–Chapman theory, the melittin binding isotherms could be described by a partition model. In terms of conventional binding mechanisms, which do not take into account electrostatic effects, this would correspond to a negative cooperativity. A plausible way in which the interaction occurs is proposed, based on the calculated Hill coefficient.
Keywords: Peptide–lipid interaction, Binding isotherm, Scatchard plot, Hill plot, Negatively cooperative binding, Partition coefficient, Ionic strength, Salt effect, Melittin