Reversible disc-to-vesicle transition of melittin-DPPC complexes triggered by the phospholipid acyl chain melting

AbstractFreeze-fracture electron microscopy, quasi-elastic light scattering and 31P solid-state NMR have been utilized in order to follow morphological changes of melittin-dipalmitoylphosphatidylcholine complexes as a function of temperature. For lipid-to-protein molar ratios greater than 10 and up to 30, a reversible transition occurs, from discoidal structures of diameter ~ 100 to 400 Å, at low temperature, to vesicular structures of diameter ~ 3000–6000 Å, at high temperature. This transition appears to be triggered by the phospholipid acyl chain melting. Higher concentrations of melittin (e.g. lipid-to-protein ratio of 5.2) prevent this morphological transition, i.e. small complexes of ~ 100–250 Å diameter remain stable throughout the temperature range.MelittinPhospholipid membraneDisc-to-vesicle transitionChain meltingNMRFreeze-fractureQuasi-elastic light scatterin