Quantifying the effects of melittin on liposomes
J F Popplewell1, M J Swann, N J Freeman
1Farfield Scientific Ltd, Farfield House, Southmere Court, Electra Way, Crewe Business Park, Crewe CW1 6GU2, UK.
Abstract:
Melittin, the soluble peptide of bee venom, has been demonstrated to induce lysis of phospholipid liposomes. We have investigated the dependence of the lytic activity of melittin on lipid composition. The lysis of liposomes, measured by following their mass and dimensions when immobilised on a solid substrate, was close to zero when the negatively charged lipids phosphatidyl glycerol or phosphatidyl serine were used as the phospholipid component of the liposome. Whilst there was significant binding of melittin to the liposomes, there was little net change in their diameter with melittin binding reversed upon salt injection. For the zwitterionic phosphatidyl choline the lytic ability of melittin is dependent on the degree of acyl chain unsaturation, with melittin able to induce lysis of liposomes in the liquid crystalline state, whilst those in the gel state showed strong resistance to lysis. By directly measuring the dimensions and mass changes of liposomes on exposure to melittin using Dual Polarisation Interferometry, rather than following the florescence of entrapped dyes we attained further information about the initial stages of melittin binding to liposomes.
Insights
Melittin from bee venom lyses liposomes, but its effectiveness depends on lipid composition. Negatively charged lipids resist lysis, while unsaturated phosphatidylcholine liposomes are susceptible, unlike saturated ones.
Area of Science:
- Biochemistry
- Biophysics
- Materials Science
Background:
- Melittin, a peptide from bee venom, is known to disrupt phospholipid bilayers.
- Understanding melittin's interaction with liposomes is crucial for its therapeutic and biotechnological applications.
Purpose of the Study:
- To investigate how lipid composition influences the lytic activity of melittin on liposomes.
- To characterize the initial stages of melittin binding to liposomes using a label-free technique.
Main Methods:
- Liposomes composed of different phospholipids (negatively charged and zwitterionic) were prepared.
- Liposome lysis was measured by monitoring mass and dimensions using Dual Polarisation Interferometry (DPI).
- Melittin binding and its effect on liposome integrity were assessed under varying salt concentrations.
Main Results:
- Melittin showed minimal lytic activity against liposomes made of negatively charged lipids (phosphatidyl glycerol, phosphatidyl serine).
- For zwitterionic phosphatidylcholine liposomes, melittin induced lysis only in the liquid crystalline state, not the gel state.
- DPI measurements provided insights into melittin binding dynamics and liposome structural changes.
Conclusions:
- The lytic activity of melittin is highly dependent on the charge and physical state of the liposome membrane.
- Dual Polarisation Interferometry offers a sensitive method to study peptide-lipid interactions without the need for fluorescent labels.
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