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Updated: May 26, 2026
Measuring Peptide Translocation into Large Unilamellar Vesicles
Published on: January 27, 2012
Slow insertion kinetics during interaction of a model antimicrobial peptide with unilamellar phospholipid vesicles
Zubaidah Ningsih1, Mohammed Akhter Hossain, John D Wade
1School of Chemistry, University of Melbourne, Parkville, Victoria 3010, Australia.
Abstract:
The mechanism of interaction between a model antimicrobial peptide and phospholipid unilamellar vesicle membranes was studied using fluorescence spectroscopy, fluorescence lifetime measurements, and light scattering. The peptide, a mellitin mutant, was labeled at position K14 with the polarity-sensitive probe AlexaFluor 430. The kinetics of the interaction of this derivative with various concentrations of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) vesicles was examined. Our work unveiled two novel aspects of peptide-lipid interactions. First, the AB plot or phasor analysis of the fluorescence lifetime studies revealed at least three different peptide states, the population of which depended on the lipid to peptide (L:P) concentration ratio. Second, complex fluorescence kinetics were observed over extended time-scales from 30 s to 2 h. The extended kinetics was only observed at particular lipid concentrations (L:P ratios 20:1 and 10:1) and not at others (30, 40, 50 and 100:1 L:P ratio). Analysis of the complex kinetics revealed several intermediates. We assign these to distinct states of the peptide formed during helix insertion into the vesicle membrane that are intermediate to lytic pore formation.
Insights
This study reveals how antimicrobial peptides interact with lipid membranes, identifying multiple peptide states and complex kinetics during pore formation. Understanding these peptide-lipid interactions is key for developing new antimicrobial therapies.
Area of Science:
- Biophysics
- Membrane Biophysics
- Antimicrobial Peptides
Background:
- Antimicrobial peptides (AMPs) are crucial in innate immunity.
- Understanding AMP-membrane interactions is vital for developing new therapeutics.
- Model systems like phospholipid vesicles are used to study these interactions.
Purpose of the Study:
- To elucidate the mechanism of interaction between a model antimicrobial peptide and phospholipid vesicle membranes.
- To investigate the peptide's conformational changes and kinetic behavior during membrane interaction.
- To identify intermediate states in the peptide's pathway to pore formation.
Main Methods:
- Fluorescence spectroscopy
- Fluorescence lifetime measurements (phasor analysis)
- Light scattering
- Utilized a K14-labeled mellitin mutant (AlexaFluor 430) and 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) vesicles.
Main Results:
- Identified at least three distinct peptide states dependent on the lipid-to-peptide (L:P) ratio.
- Observed complex fluorescence kinetics over extended timescales (30s to 2h) at specific L:P ratios (20:1 and 10:1).
- Revealed several intermediate states during helix insertion into the vesicle membrane, preceding lytic pore formation.
Conclusions:
- The study provides novel insights into the dynamic nature of peptide-lipid interactions.
- Multiple peptide conformations and kinetic intermediates are involved in the membrane disruption process.
- Findings contribute to understanding the mechanism of antimicrobial peptide action and pore formation.
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