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The lipid charge density at the bilayer surface modulates the effects of melittin on membranes
1Centre de Recherche Paul Pascal, CNRS, Pessac, France.
Abstract:
The influence of melittin on two DMPA membrane systems at pH 4.2 and 8.2 has been investigated by solid-state 31P and 2H NMR, as a function of temperature and peptide concentration. Melittin promotes greater morphological changes for both systems in the fluid phase, the effect being 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 31P 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 gel phase one observes an intermediate hexagonal phase in a narrow range of temperature.
Insights
Melittin significantly alters dimyristoylphosphatidic acid (DMPA) membrane structures, especially at lower pH. This peptide induces morphological changes, forming inverted micelles and hexagonal phases in DMPA lipid systems.
Area of Science:
- Biophysics
- Membrane Biophysics
- Biochemistry
Background:
- Melittin, a peptide from bee venom, is known to interact with lipid bilayers.
- The behavior of phospholipids like dimyristoylphosphatidic acid (DMPA) in membranes is crucial for understanding cellular processes.
- Investigating peptide-lipid interactions provides insights into membrane structure and dynamics.
Purpose of the Study:
- To investigate the influence of melittin on DMPA membrane systems at different pH values (4.2 and 8.2).
- To elucidate the morphological and dynamic changes induced by melittin in DMPA membranes.
- To understand the molecular mechanisms of melittin-lipid interactions.
Main Methods:
- Solid-state 31P and 2H Nuclear Magnetic Resonance (NMR) spectroscopy were employed.
- Experiments were conducted as a function of temperature and peptide concentration.
- Analysis focused on lipid acyl chain dynamics and membrane phase behavior.
Main Results:
- Melittin induced greater morphological changes in fluid-phase DMPA systems, with more pronounced effects at pH 4.2.
- At pH 8.2, melittin interactions with DMPA showed similarities to melittin interactions with phosphatidylcholine (PC) systems.
- At pH 4.2 and high temperatures, a lipid-to-peptide ratio of 30 transformed the system into isotropic inverted micelles, transitioning to a hexagonal phase upon cooling.
Conclusions:
- Melittin significantly impacts DMPA membrane morphology, with pH-dependent effects.
- The study reveals specific molecular interactions, including charge neutralization at the lipid-peptide interface at pH 8.2.
- Melittin can induce distinct phase transitions in DMPA systems, highlighting its potent membrane-disrupting capabilities.