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Lipid-gramicidin interactions using two-dimensional Fourier-transform electron spin resonance
B R Patyal1, R H Crepeau, J H Freed
1Baker Laboratory of Chemistry, Cornell University, Ithaca, New York 14853, USA.
Biophysical Journal
|October 23, 1997
Summary
Two-dimensional Fourier-transform electron-spin-resonance (2D-FT-ESR) reveals how gramicidin A affects lipid dynamics in membranes. This advanced technique shows gramicidin A significantly slows lipid diffusion while only slightly increasing ordering.
Area of Science:
- Biophysical Chemistry
- Membrane Biophysics
- Spectroscopy
Background:
- Understanding lipid-protein interactions is crucial for membrane function.
- Electron-spin-resonance (ESR) spectroscopy is a powerful tool for studying membrane dynamics.
- Two-dimensional Fourier-transform ESR (2D-FT-ESR) offers enhanced resolution over conventional continuous-wave ESR (cw-ESR).
Purpose of the Study:
- To investigate the effects of gramicidin A (GA) on the dynamics and ordering of dipalmitoylphosphatidylcholine (DPPC) lipid membranes using 2D-FT-ESR.
- To compare the capabilities of 2D-FT-ESR with cw-ESR for characterizing lipid-protein interactions.
- To analyze the influence of GA on lipid diffusion and order parameters in different lipid phases.
Main Methods:
- Utilized two-dimensional Fourier-transform electron-spin-resonance (2D-FT-ESR) spectroscopy.
- Employed 16-PC as a lipid spin label in dipalmitoylphosphatidylcholine (DPPC) membrane vesicles.
- Analyzed spectral data in both liquid crystalline and gel phases of the lipid bilayer.
- Performed spectral simulations to interpret experimental findings and validate theoretical models.
Main Results:
- 2D-FT-ESR provided significantly improved spectral resolution compared to cw-ESR for detecting changes in lipid dynamics and ordering upon GA addition.
- Gramicidin A substantially decreased both rotational and translational diffusion rates of bulk lipids in the liquid crystalline phase at a 1:5 GA to lipid ratio.
- GA addition resulted in only a slight increase in lipid ordering in the liquid crystalline phase.
- The slowing effect of GA on lipid diffusion was less pronounced in the gel phase.
- 2D-FT-ESR did not show evidence for a second immobilized lipid component, unlike cw-ESR, suggesting this component is characterized by reduced diffusion rather than increased ordering.
Conclusions:
- 2D-FT-ESR is a superior technique for resolving subtle changes in lipid dynamics and ordering induced by membrane-bound peptides like gramicidin A.
- Gramicidin A significantly impacts lipid mobility, primarily by reducing diffusion rates, with a lesser effect on lipid ordering.
- The study provides insights into the dynamic behavior of lipids in the presence of gramicidin A and highlights the advantages of 2D-FT-ESR for such investigations.