Open AccessPhysical modifications of rhodopsin boundary lipids in lecithin-rhodopsin complexes: a spin-label study.
Author(s) -
Jean Davoust,
Bernard Schoot,
Philippe F. Devaux
Publication year - 1979
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.76.6.2755
Subject(s) - microviscosity , rhodopsin , chemistry , electron paramagnetic resonance , spin label , lecithin , biophysics , retinal , biochemistry , membrane , nuclear magnetic resonance , biology , physics
The microviscosity of rhodopsin boundary lipids was studied with a spin-labeled fatty acid covalently attached to rhodopsin, in rhodopsin-egg lecithin vesicles. When the lipid-to-protein ratio was high (500:1, mole to mole), only narrow peaks were visible in electron paramagnetic resonance spectrum at 37 degrees C. This enabled us to show that, under these conditions, not more than 10% of the probes have their motion strongly restricted by the proximity of the protein. When the temperature was reduced, a second component characteristic of strong immobilization appeared. It corresponds to 50% of the signal at -5 degrees C. At all temperatures reduction of the lipid-to-protein ratio also resulted in an increase of the amount of immobilized lipid. These results show that the rhodopsin boundary layer under physiological conditions is associated with low microviscosity. However, low temperatures, low lipid-to-protein ratios, or combinations of the two can induce dramatic modifications of the physical state of the boundary lipids, which under these conditions may no longer be representative of the functional biological system. These results are relevant to the general theory of lipid-protein interaction.