Protein-induced vertical lipid dislocation in a model membrane system: spin-label relaxation studies on avidin-biotinylphosphatidylethanolamine interactions.
The change in vertical location of spin-labeled N-biotinyl phosphatidylethanolamine in fluid-phase dimyristoyl phosphatidylcholine bilayer membranes, on binding avidin to the biotinyl headgroup, has been investigated by progressive saturation electron spin resonance measurements. Spin-labeled phospholipids were present at a concentration of 1 mol%, relative to total membrane lipids. For avidin-bound N-biotinyl phosphatidylethanolamine spin-labeled on the 8 C atom of the sn-2 chain, the relaxation enhancement induced by 30 mM Ni2+ ions confined to the aqueous phase was 2.5 times that induced by saturating molecular oxygen, which is preferentially concentrated in the hydrophobic core of the membrane. For phosphatidylcholine also spin-labeled at the 8 position of the sn-2 chain, this ratio was reversed: the relaxation enhancement by Ni2+ ions was half that induced by molecular oxygen. In the absence of avidin, the enhancement by either relaxant was the same for both spin-labeled phospholipids. For a double-labeled system, in which both N-biotinyl phosphatidylethanolamine and phosphatidylcholine were spin-labeled on the 12 C atom of the sn-2 chain, the relaxation rate in the absence of avidin was greater than that predicted from linear additivity of the corresponding singly labeled systems, because of mutual spin-spin interactions between the two labeled lipid species. On binding of avidin to the N-biotinyl phosphatidylethanolamine, this relaxation enhancement by mutual spin-spin interaction was very much decreased. These results indicate that, on binding of avidin to the lipid headgroup, N-biotinyl phosphatidylethanolamine is lifted vertically within the membrane, relative to the phosphatidylcholine host lipids. The specific binding of avidin to N-biotinyl phosphatidylethanolamine parallels the liftase activity proposed for activator proteins associated with the action of certain gangliosidases.
Arora
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Max-Planck-Institut für biophysikalische Chemie, Abteilung Spektroskopie, D-37070 Göttingen, Germany.
Marsh
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D
D000818:Animals; D001360:Avidin / Q000737:chemistry; D055592:Biophysical Phenomena; D001703:Biophysics; D001710:Biotin / Q000031:analogs & derivatives / Q000737:chemistry; D002645:Chickens; D004578:Electron Spin Resonance Spectroscopy; D066298:In Vitro Techniques; D008563:Membrane Lipids / Q000737:chemistry*; D008565:Membrane Proteins / Q000737:chemistry*; D008567:Membranes, Artificial; D008956:Models, Chemical; D008958:Models, Molecular; D010714:Phosphatidylethanolamines / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D013113:Spin Labels; D019809:Streptavidin / Q000737:chemistry
D008563:Membrane Lipids; D008565:Membrane Proteins; D008567:Membranes, Artificial; C072348:N-biotinylphosphatidylethanolamine; D010714:Phosphatidylethanolamines; D013113:Spin Labels; D001360:Avidin; D001710:Biotin; D019809:Streptavidin