Location of Cholesterol in Model Membranes by Magic‐Angle‐Sample‐Spinning NMR

Abstract

High-resolution magic-angle-sample-spinning ' 3C-NMR was applied to determine the specific location of cholesterol in non-perturbed multilamellar model membranes formed by egg yolk phosphatidylcholine. "C spin-lattice relaxation times of both the phospholipid and cholesterol molecules were measured in the absence and in the presence of Gd3+, a paramagnetic agent, in order to obtain information on molecular distances. The effect of Gd3+ 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.

Probing membrane topology by high-resolution 1H–13C heteronuclear dipolar solid-state NMR spectroscopy

“…Similar deshielding effects in the lipids acyl chain region were also observed in lipid bilayers upon incorporation of cholesterol due to higher molecular ordering [12]. Unlike the large headgroup of DMPC, cholesterol has only a small OH group positioned in the vicinity of the fatty ester groups of the phospholipids [20]. This explains the reduced perturbation observed in the lipid glycerol and headgroup regions upon incorporation of cholesterol.…”

Membrane-dependent oligomeric structure and pore formation of a β-hairpin antimicrobial peptide in lipid bilayers from solid-state NMR

“…The CH 3 buildup curve is very similar to that of a DNA-lipid complex, where the anionic DNA is sandwiched between bilayers with cationic headgroups, 20 Å from the bilayer center (11). The surface location of PG-1 in POPC͞cholesterol bilayers is reasonable, because cholesterol inserts into the hydrophobic and glycerol regions of the bilayer (37), and thus should exert a negative curvature strain that counters PG-1 insertion (Fig. 6a).…”

Probing Membrane Surfaces and the Location of Membrane-Embedded Peptides by 13C MAS NMR Using Lanthanide Ions

“…For pure lipid bilayers, spectral resolution is sufficient for a complete assignment of all carbon atoms in a lipid molecule (4). Thus, the influence of membrane effectors, such as cholesterol, has been studied simultaneously at atomic resolution at all positions of the lipid and sterol molecules providing a comprehensive picture across the whole bilayer (4 -7).To probe the location of membrane compounds relative to the membrane surface, a method is presented based on a site-resolved observation of the nuclear spin-relaxation-enhancement effect through paramagnetic probes (5,8), by using a combination of Dy 3ϩ ions bound to dimyristoylphosphatidylcholine (DMPC) bilayers and high-resolution 13 C CP MAS NMR. The binding of this trivalent ion to the bilayer surface permits observation of quenching of resonances arising from the different sites of embedded molecules which are in close proximity to the polar interface or outside the membrane.…”