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Detailed comparison of deuterium quadrupole profiles between sphingomyelin and phosphatidylcholine bilayers.

ABSTRACT: Lipid rafts are microdomains rich in sphingomyelin (SM) and cholesterol (Chol). The essential question is why natural lipid rafts prefer SM rather than saturated diacyl glycerophosphocholine, although both form ordered membranes with Chol in model systems. Hence in this study, we synthesized site-specifically deuterated 1-palmitoyl-2-stearoyl-sn-glycero-3-phosphocholines that match the acyl chain length of stearoyl-SM (SSM), and compared their deuterium quadrupole coupling profiles in detail. The results suggest a deeper distribution of Chol in the SSM membranes, a lower entropic penalty upon accommodation of Chol in SSM membranes, and a higher thermal stability of acyl-chain orders in the SSM-Chol bilayers than in the 1-palmitoyl-2-stearoyl-sn-glycero-3-phosphocholine-Chol system at various Chol concentrations. The entropy effect and thermal stability should render SM a more preferred raft constituent than saturated diacyl glycerophosphocholine. Our data also demonstrate that the selective and comprehensive deuteration strategy is indispensable for accurate comparison of order profiles.

SUBMITTER: Yasuda T

PROVIDER: S-EPMC3944833 | biostudies-literature | 2014 Feb

REPOSITORIES: biostudies-literature

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Detailed comparison of deuterium quadrupole profiles between sphingomyelin and phosphatidylcholine bilayers.

Yasuda Tomokazu T Kinoshita Masanao M Murata Michio M Matsumori Nobuaki N

Biophysical journal 20140201 3

Lipid rafts are microdomains rich in sphingomyelin (SM) and cholesterol (Chol). The essential question is why natural lipid rafts prefer SM rather than saturated diacyl glycerophosphocholine, although both form ordered membranes with Chol in model systems. Hence in this study, we synthesized site-specifically deuterated 1-palmitoyl-2-stearoyl-sn-glycero-3-phosphocholines that match the acyl chain length of stearoyl-SM (SSM), and compared their deuterium quadrupole coupling profiles in detail. Th ...[more]

PMID: 24507603

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Project description:The interaction between cholesterol and phospholipids in bilayer membranes is important for the formation and maintenance of membrane structure and function. However, cholesterol does not interact favorably with all types of phospholipids and, for example, prefers more ordered sphingomyelins (SMs) over phosphatidylcholines (PCs). The reason for this preference is not clear. Here we have studied whether acyl-chain order could be responsible for the preferred sterol interaction with SMs. Acyl-chain order was deduced from diphenylhexatriene anisotropy and from the deuterium order parameter obtained by (2)H-NMR on bilayers made from either 14:0/14:0((d27))-PC, or 14:0((d27))-SM. Sterol/phospholipid interaction was determined from sterol bilayer partitioning. Cholestatrienol (CTL) was used as a fluorescence probe for cholesterol, because its relative membrane partitioning is similar to cholesterol. When CTL was allowed to reach equilibrium partitioning between cyclodextrins and unilamellar vesicles made from either 14:0/14:0-PC or 14:0-SM, the molar-fraction partitioning coefficient (K(x)) was approximately twofold higher for SM bilayers than for PC bilayers. This was even the case when the temperature in the SM samples was raised to achieve equal acyl-chain order, as determined from 1,6-diphenyl-1,3,5-hexatriene (DPH) anisotropy and the deuterium order parameter. Although the K(x) did increase with acyl-chain order, the higher K(x) for SM bilayers was always evident. At equal acyl-chain order parameter (DPH anisotropy), the K(x) was also higher for 14:0-SM bilayers than for bilayers made from either 14:0/15:0-PC or 15:0-/14:0-PC, suggesting that minor differences in chain length or molecular asymmetry are not responsible for the difference in K(x). We conclude that acyl-chain order affects the bilayer affinity of CTL (and thus cholesterol), but that it is not the cause for the preferred affinity of sterols for SMs over matched PCs. Instead, it is likely that the interfacial properties of SMs influence and stabilize interactions with sterols in bilayer membranes.

Project description:Sphingomyelin, one of the main lipid components of biological membranes, is actively involved in various cellular processes such as protein trafficking and signal transduction. In particular, specific lateral domains enriched in sphingomyelin and cholesterol have been proposed to play an important functional role in biomembranes, although their precise characteristics have remained unclear. A thorough understanding of the functional role of membranes requires detailed knowledge of their individual lipid components. Here, we employ molecular dynamics simulations to conduct a systematic comparison of a palmitoylsphingomyelin (PSM, 16:0-SM) bilayer with a membrane that comprises dipalmitoylphosphatidylcholine (DPPC) above the main phase transition temperature. We clarify atomic-scale properties that are specific to sphingomyelin due to its sphingosine moiety, and further discuss their implications for SM-rich membranes. We find that PSM bilayers, and in particular the dynamics of PSM systems, are distinctly different from those of a DPPC bilayer. When compared with DPPC, the strong hydrogen bonding properties characteristic to PSM are observed to lead to considerable structural changes in the polar headgroup and interface regions. The strong ordering of PSM acyl chains and specific ordering effects in the vicinity of a PSM-water interface reflect this issue clearly. The sphingosine moiety and related hydrogen bonding further play a crucial role in the dynamics of PSM bilayers, as most dynamic properties, such as lateral and rotational diffusion, are strongly suppressed. This is most evident in the rotational motion characterized by spin-lattice relaxation times and the decay of hydrogen bond autocorrelation functions that are expected to be important in complexation of SM with other lipids in many-component bilayers. A thorough understanding of SM bilayers would greatly benefit from nuclear magnetic resonance experiments for acyl chain ordering and dynamics, allowing full comparison of these simulations to experiments.

Project description:The mode of interactions between palmitoyl lysophosphatidylcholine (palmitoyl lyso-PC) or other lysophospholipids (lyso-PLs) and palmitoyl ceramide (PCer) or other ceramide analogs in dioleoylphosphatidylcholine (DOPC) bilayers has been examined. PCer is known to segregate laterally into a ceramide-rich phase at concentrations that depend on the nature of the ceramides and the co-phospholipids. In DOPC bilayers, PCer forms a ceramide-rich phase at concentrations above 10 mol%. In the presence of 20 mol% palmitoyl lyso-PC in the DOPC bilayer, the lateral segregation of PCer was markedly facilitated (segregation at lower PCer concentrations). The thermostability of the PCer-rich phase in the presence of palmitoyl lyso-PC was also increased compared to that in the absence of palmitoyl lyso-PC. Other saturated lyso-PLs (e.g., palmitoyl lyso-phosphatidylethanolamine and lyso-sphingomyelin) also facilitated the lateral segregation of PCer in a similar manner as palmitoyl lyso-PC. When examined in the DOPC bilayer, it appeared that the association between palmitoyl lyso-PC and PCer was equimolar in nature. It is proposed that the interaction of PCer with lyso-PLs was driven by the need of ceramide to obtain a large-headgroup co-lipid, and saturated lyso-PLs were preferred co-lipids over DOPC because of the nature of their acyl chain. Structural analogs of PCer (1- or 3-deoxy-PCer) were also associated with palmitoyl lyso-PC, similarly to PCer, suggesting that the ceramide/lyso-PL interaction was not sensitive to structural alterations in the ceramide molecule. Binary complexes containing palmitoyl lyso-PC and ceramide were prepared, and these had a bilayer structure as ascertained by transmission electron microscopy. It is concluded that ceramides and lyso-PLs associated with each other both in binary bilayers and in ternary systems based on the DOPC bilayers. This association may have biological relevance under conditions in which both sphingomyelinases and phospholipase A2 enzymes are activated, such as during inflammatory processes.

Dataset Information

Detailed comparison of deuterium quadrupole profiles between sphingomyelin and phosphatidylcholine bilayers.

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Detailed comparison of deuterium quadrupole profiles between sphingomyelin and phosphatidylcholine bilayers.

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