Conformation of spin-labeled melittin at membrane surfaces investigated by pulse saturation recovery and continuous wave power saturation electron paramagnetic resonance.
Melittin spin-labeled specifically with a nitroxide at positions 7, 21, 23, or the amino terminus was bound to phospholipid membranes, and the exposure of the spin label to the aqueous phase was investigated by measurement of Heisenberg exchange with chromium oxalate in the solution. The exchange frequency was determined by saturation recovery electron paramagnetic resonance (EPR) using a loop-gap resonator. This method allows use of very low concentrations (less than 1 mM) of chromium oxalate compared with conventional measurements of EPR line broadening (typically 50 mM), thus avoiding problems associated with high metal ion concentration. Differences in exchange frequency between the various positions were also estimated by continuous wave power saturation methods. In either approach, the spin label at lysine 7 was found to be the most exposed to chromium oxalate whereas that at lysine 23 was found to be the least exposed. This is consistent with a model for the membrane bound peptide in which an amphiphilic helix lies with its axis parallel to the bilayer surface and the hydrophobic moment points toward the bilayer interior.
Altenbach
C
C
Jules Stein Eye Institute, University of California, Los Angeles 90024-1771.
Froncisz
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W
Hyde
J S
JS
Hubbell
W L
WL
D000595:Amino Acid Sequence; D001514:Bee Venoms; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D004594:Electrophysiology / Q000379:methods; D008081:Liposomes; D008555:Melitten; D008954:Models, Biological; D008969:Molecular Sequence Data; D010713:Phosphatidylcholines; D011485:Protein Binding; D011487:Protein Conformation; D013113:Spin Labels
D001514:Bee Venoms; D008081:Liposomes; D010713:Phosphatidylcholines; D013113:Spin Labels; D008555:Melitten