A Solid-State NMR Study of Phospholipid-Cholesterol Interactions: Sphingomyelin-Cholesterol Binary Systems

Abstract

We used solid-state NMR techniques to probe the interactions of cholesterol (Chol) with bovine brain sphingomyelin (SM) and for comparison of the interactions of Chol with dipalmitoylphosphatidylcholine (DPPC), which has a similar gel-to-liquid crystalline transition temperature. (1)H-, (31)P-, and (13)C-MASNMR yielded high-resolution spectra from multilamellar dispersions of unlabeled brain SM and Chol for analysis of chemical shifts and linewidths. In addition, (2)H-NMR spectra of oriented lipid membranes with specific deuterium labels gave information about membrane ordering and mobility. Chol disrupted the gel-phase of pure SM and increased acyl chain ordering in the liquid crystalline phase. As inferred from (13)C chemical shifts, the boundaries between the ordered and disordered liquid crystalline phases (L and L) were similar for SM and DPPC. The solubility limit of Chol in SM was ~50 mol %, the same value as previously reported for DPPC membranes. We found no evidence for specific H-bonding between Chol and the amide group of SM. The order parameters of a probe molecule, d31-sn1-DPPC, in SM were slightly higher than in DPPC for all carbons except the terminal groups at 30 mol % but were not significantly different at 5 and 60 mol % Chol. These studies show a general similarity with some subtle differences in the way Chol interacts with DPPC and SM. In the environment of a typical biomembrane, the higher proportion of saturated fatty acyl chains in SM compared to other phospholipids may be the most significant factor influencing interactions with Chol.

Photophysical studies of zinc phthalocyanine and chloroaluminum phthalocyanine incorporated into liposomes in the presence of additives

“…Mol fractions higher than 0.5 of cholesterol are required for cluster formation with phosphatidylcholine (24)(25)(26). When the cholesterol content exceeds the saturation limit in phospholipid membranes, crystalline cholesterol monohydrate forms (27,28). In general, for choline phospholipids the saturation limit is ≈50% cholesterol, although a higher solubility (65%) has been reported by Huang et al (29) and a solubility higher than 60% was obtained by Guo and Hamilton (27).…”

Tales and Mysteries of the Enigmatic Sphingomyelin Synthase Family

“…[49][50][51][52][53] Recent evidence has further enriched this model supporting a role for SM in the homeostasis of lipid microdomains at the plasma membrane, often sites of receptor-mediated signaling. Taking advantage of the identification of SMS1 as bona fide SM synthase, the role of SM in the activation of Fas signaling was investigated by Miyaji et al 75 Comparing SMS1 deficient cells (with over expressed Fas receptor) with cells in which expression of SMS1 was restored, the authors provide evidence for a critical role of SM in Fas-mediated signaling by enabling the formation of the death-inducing signaling complex (DISC) and consequently allowing caspase activation and production of ceramide at the plasma membrane.…”

“…In fact, the predominant presence of saturated fatty acids and the potential intermolecular hydrogen binding, via the amide bond and the free hydroxyl group at position 3, favor a high-density packing of SM, which increases the compactness and impermeability of the membrane. [51][52][53] According to the umbrella model, 54 the preferential mixing of sterols with SM is caused by shielding of the nonpolar sterol molecule by the phosphocholine head group of SM. Collectively these physicochemical features are believed to influence the lateral organization of cellular membranes.…”

Yeast Lipids Can Phase-separate into Micrometer-scale Membrane Domains

“…In addition, experimental and computational data suggest that hydrogen bonds between SM and cholesterol might facilitate their interaction, presumably via the amide group of SM and the 3-hydroxyl of cholesterol (55,56). Alternatively, charge pairing between the headgroup nitrogen of SM and the 3-hydroxyl of cholesterol was proposed to be involved in the SM-cholesterol interaction (57,58). Because the order of IPC/ergosterol membranes is comparable with SM/cholesterol membranes (Fig.…”