Open AccessLocation of Cholesterol in Model Membranes by Magic‐Angle‐Sample‐Spinning NMR
Author(s) -
Villalaín José
Publication year - 1996
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1996.00586.x
Subject(s) - phospholipid , membrane , magic angle spinning , chemistry , phosphatidylcholine , bilayer , lipid bilayer , magic angle , crystallography , spin–lattice relaxation , biological membrane , molecule , relaxation (psychology) , solid state nuclear magnetic resonance , nuclear magnetic resonance spectroscopy , nuclear magnetic resonance , stereochemistry , organic chemistry , biochemistry , psychology , social psychology , physics , nuclear quadrupole resonance
High‐resolution magic‐angle‐sample‐spinning 13 C‐NMR was applied to determine the specific location of cholesterol in non‐perturbed multilamellar model membranes formed by egg yolk phosphatidylcholine. 13 C spin‐lattice relaxation times of both the phospholipid and cholesterol molecules were measured in the absence and in the presence of Gd 3+ , a paramagnetic agent, in order to obtain information on molecular distances. The effect of Gd 3+ on the spin‐lattice relaxation times of the lipid resonances has an explicit distance dependence, allowing it to be used to evaluate relative distances on a molecular scale. It has been found that cholesterol is placed in such a position that it is not readily exposed to the solvent: the hydrophobic steroid ring is oriented parallel to the membrane phospholipids, the hydroxyl group is in close vicinity to the phospholipid ester carbonyl groups and the isooctyl side chain is deeply buried in the center of the membrane. These data are consistent with an organization such that mixtures of cholesterol and phospholipids present a packing similar to that found in interdigitated lipid bilayer systems.