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 ha s been investigated by solid-state P-31 and H-2 NMR, as a function of tempe rature and peptide concentration. Melittin promotes greater morphological c hanges 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 parall els can be drawn between the DMPA/melittin at pH 8.2 and PC-melittin system s. In addition. at pH 8.2 a direct neutralization at the interface of one o f 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 suffic ient 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.