Intramembrane water associated with TOAC spin-labeled alamethicin: electron spin-echo envelope modulation by D2O
R Bartucci1, R Guzzi, L Sportelli
1Dipartimento di Fisica and Unità di Recerca Consorzio Nazionale Interuniversitario per le Scienze fisiche della Materia, Università della Calabria, Arcavacata di Rende, Italy.
Biophysical Journal
|February 3, 2009
Summary
Alamethicin peptide orientation in lipid membranes differs based on lipid saturation. Water exposure profiles reveal distinct transmembrane or superficial locations, influenced by lipid type and peptide concentration.
Area of Science:
- Biophysics
- Membrane protein structure
- Spectroscopy
Background:
- Alamethicin forms voltage-sensitive ion channels in lipid bilayers.
- Hydrophobic peptides like alamethicin are crucial for membrane function.
- Understanding peptide-lipid interactions is key to ion channel mechanisms.
Purpose of the Study:
- To investigate the water exposure and assembly of alamethicin analogs in different lipid membranes.
- To determine the orientation and location of alamethicin residues within saturated and unsaturated lipid bilayers.
- To correlate peptide location with membrane phase and lipid composition.
Main Methods:
- Electron spin-echo envelope modulation (ESEEM) spectroscopy using TOAC-alamethicin analogs.
- Echo-detected Electron Paramagnetic Resonance (EPR) to assess peptide assembly.
- Utilizing deuterium oxide (D2O) to probe water accessibility of peptide residues.
- Comparing results in saturated (DMPC) and unsaturated (DOPC) phosphatidylcholine membranes.
Main Results:
- Water exposure profiles of TOAC-alamethicin varied significantly between saturated and unsaturated lipid membranes.
- In unsaturated lipids, a transmembrane orientation was suggested, with residues unequally exposed to water.
- In saturated lipids, alamethicin adopted a more superficial location, with residue 8 showing highest water exposure.
- Higher peptide/lipid ratios in saturated lipids shifted water exposure profiles towards those seen in unsaturated lipids.
Conclusions:
- Alamethicin's orientation and water exposure are sensitive to lipid saturation and peptide concentration.
- A transition between distinct membrane-associated states (transmembrane vs. superficial) is proposed.
- These findings provide insights into the dynamic nature of peptide-lipid interactions and ion channel formation.
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