Integration of a K+ channel-associated peptide in a lipid bilayer: conformation, lipid-protein interactions, and rotational diffusion.
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)
Horváth
L I
LI
Abteilung Spektroskopie, Max-Planck-Institut für biophysikalische Chemie, Göttingen, Federal Republic of Germany.
Heimburg
T
T
Kovachev
P
P
Findlay
J B
JB
Hideg
K
K
Marsh
D
D
D000595:Amino Acid Sequence; D004058:Diffusion; D004134:Dimyristoylphosphatidylcholine / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D008051:Lipid Bilayers; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D015221:Potassium Channels / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012399:Rotation; D017550:Spectroscopy, Fourier Transform Infrared
D008051:Lipid Bilayers; D010446:Peptide Fragments; D015221:Potassium Channels; D004134:Dimyristoylphosphatidylcholine