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Integration of a K+ channel-associated peptide in a lipid bilayer: conformation, lipid-protein interactions, and
L I Horváth1, T Heimburg, P Kovachev
1Abteilung Spektroskopie, Max-Planck-Institut für biophysikalische Chemie, Göttingen, Federal Republic of Germany.
Abstract:
The 26-residue peptide of sequence KEALYILMVLGFFGFFTLGIMLSYIR, which contains the single putative transmembrane domain of a small protein that is associated with slow voltage-gated K+ channels, has been incorporated in bilayers of dimyristoylphosphatidylcholine by dialysis from 2-chloroethanol to form complexes of homogeneous lipid/peptide ratio. Fourier transform infrared spectroscopy indicates that the peptide is integrated in the lipid bilayer wholly in a beta-sheet conformation. The electron spin resonance spectra of spin-labeled lipids in the lipid/peptide complexes contain a component corresponding to lipids whose chains are motionally restricted in a manner similar to those of lipids at the hydrophobic surface of integral transmembrane proteins. From the dependence of the lipid spin label spectra on the lipid/peptide ratio of the complexes, it is found that ca. 2.5 lipids per peptide monomer, independent of the species of spin-labeled lipid, are motionally restricted by direct interaction with the peptide in the bilayer. This value would be consistent with, e.g., a beta-barrel structure for the peptide in which the beta-strands either are strongly tilted or have a reverse turn at their center. A preferential selectivity of interaction with the peptide is observed for the negatively charged spin-labeled lipids phosphatidic acid, stearic acid, and phosphatidylserine, which indicates close proximity of the positively charged residues at the peptide termini to the lipid headgroups. The saturation-transfer electron spin resonance spectra of the peptide spin-labeled at a cysteine residue replacing Leu18 evidence rather slow rotational diffusion in the lipid complexes.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
This study reveals how a peptide associated with slow voltage-gated potassium channels integrates into lipid bilayers. The peptide adopts a beta-sheet structure, restricting lipid mobility and showing selective interaction with charged lipids.
Area of Science:
- Biophysics
- Membrane Biology
- Protein-Lipid Interactions
Background:
- Small proteins associated with slow voltage-gated K+ channels play a role in cellular excitability.
- Understanding the membrane integration and conformational dynamics of such peptides is crucial for elucidating channel function.
Purpose of the Study:
- To investigate the structural integration and lipid interaction of a specific 26-residue peptide, a putative transmembrane domain, within a lipid bilayer.
- To determine the peptide's conformation and the extent of lipid chain restriction upon complex formation.
Main Methods:
- Incorporation of the peptide into dimyristoylphosphatidylcholine bilayers via dialysis.
- Fourier transform infrared spectroscopy (FTIR) to determine peptide conformation.
- Electron spin resonance (ESR) spectroscopy using spin-labeled lipids to assess lipid chain mobility and peptide-lipid interactions.
- Saturation-transfer ESR to evaluate peptide rotational diffusion.
Main Results:
- The peptide adopts a stable beta-sheet conformation within the lipid bilayer.
- Approximately 2.5 lipid molecules per peptide monomer exhibit restricted motion due to direct interaction.
- Negatively charged spin-labeled lipids show preferential interaction, suggesting proximity of charged peptide termini to lipid headgroups.
- The peptide demonstrates relatively slow rotational diffusion within the lipid complexes.
Conclusions:
- The peptide integrates into the lipid bilayer primarily in a beta-sheet conformation, likely forming a beta-barrel or similar structure.
- The peptide significantly influences lipid dynamics, restricting the motion of surrounding lipid chains.
- Specific interactions occur between the peptide termini and charged lipid headgroups, indicating orientation within the membrane.