The lipid charge density at the bilayer surface modulates the effects of melittin on membranes

The influence of melittin on two DMPA membrane systems at pH 4.2 and 8.2 has been investigated by solid-state P-31 and H-2 NMR, as a function of temperature and peptide concentration. Melittin promotes greater morphological changes for both systems in the fluid phase, the effect bring larger at pH 4.2. Close inspection of fatty acyl chain dynamics suggests that some parallels can be drawn between the DMPA/melittin at pH 8.2 and PC-melittin systems. In addition. at pH 8.2 a direct neutralization at the interface of one of the lipid negative charges by a positive charge of the peptide occurs. as can be monitored by P-31 NMR at the molecular level. For the system at pH 4.2 and at high temperature, a lipid-to-peptide molar ratio of 30 is sufficient to transform the whole system into an isotropic phase, proposed to be inverted micelles. When the system is cooled down towards the pel phase one observes an intermediate hexagonal phase in a narrow range of temperature. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.