Molecular behaviour of glycosphingolipids in interfaces. Possible participation in some properties of nerve membranes

The many faces (and phases) of ceramide and sphingomyelin II - binary mixtures

A rather widespread idea on the functional importance of sphingolipids in cell membranes refers to the occurrence of ordered domains enriched in sphingomyelin and ceramide that are largely assumed to exist irrespective of the type of N-acyl chain in the sphingolipid. Ceramides and sphingomyelins are the simplest kind of two-chained sphingolipids and show a variety of species, depending on the fatty acyl chain length, hydroxylation, and unsaturation. Abundant evidences have shown that variations of the N-acyl chain length in ceramides and sphingomyelins markedly affect their phase state, interfacial elasticity, surface topography, electrostatics, and miscibility, and that even the usually conceived "condensed" sphingolipids and many of their mixtures may exhibit liquid-like expanded states. Their lateral miscibility properties are subtlety regulated by those chemical differences. Even between ceramides with different acyl chain length, their partial miscibility is responsible for a rich two-dimensional structural variety that impacts on the membrane properties at the mesoscale level. In this review, we will discuss the miscibility properties of ceramide, sphingomyelin, and glycosphingolipids that differ in their N-acyl or oligosaccharide chains. This work is a second part that accompanies a previous overview of the properties of membranes formed by pure ceramides or sphingomyelins, which is also included in this Special Issue.

Carbohydrate conformation and lipid condensation in monolayers containing glycosphingolipid Gb3: influence of acyl chain structure

Globotriaosylceramide (Gb3), a glycosphingolipid found in the plasma membrane of animal cells, is the endocytic receptor of the bacterial Shiga toxin. Using x-ray reflectivity (XR) and grazing incidence x-ray diffraction (GIXD), lipid monolayers containing Gb3 were investigated at the air-water interface. XR probed Gb3 carbohydrate conformation normal to the interface, whereas GIXD precisely characterized Gb3's influence on acyl chain in-plane packing and area per molecule (APM). Two phospholipids, 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE), were used to study Gb3 packing in different lipid environments. Furthermore, the impact on monolayer structure of a naturally extracted Gb3 mixture was compared to synthetic Gb3 species with uniquely defined acyl chain structures. XR results showed that lipid environment and Gb3 acyl chain structure impact carbohydrate conformation with greater solvent accessibility observed for smaller phospholipid headgroups and long Gb3 acyl chains. In general, GIXD showed that Gb3 condensed phospholipid packing resulting in smaller APM than predicted by ideal mixing. Gb3's capacity to condense APM was larger for DSPC monolayers and exhibited different dependencies on acyl chain structure depending on the lipid environment. The interplay between Gb3-induced changes in lipid packing and the lipid environment's impact on carbohydrate conformation has broad implications for glycosphingolipid macromolecule recognition and ligand binding.

Ceramide N-acyl chain length: a determinant of bidimensional transitions, condensed domain morphology, and interfacial thickness

Several lipids of biological interest are able to form monomolecular surfaces with a rich variety of thickness and lateral topography that can be precisely controlled by defined variations of the film composition. Ceramide is one of the simplest sphingolipids, consisting of a sphingosine base N-linked to a fatty acid, and is a membrane mediator for cell-signaling events. In this work, films of ceramides N-acylated with the saturated fatty acids C10, C12, C14, and C16 were studied at the air-aqueous interface. The dipole moment contribution (from surface potential measurements) and the surface topography and thickness (as revealed by Brewster angle microscopy) were measured simultaneously with the surface pressure at different molecular areas. Several surface features were observed depending on the asymmetry between the sphingosine and the N-linked acyl chains. At 21 °C, the C16:0 and C14:0 ceramides showed condensed isotherms and the film topography revealed solid film patches (17.3-15.7 Å thick) that coalesced into a homogeneous surface by further compression. On the other hand, in the more asymmetric C12:0 and C10:0 ceramides, liquid expanded states and liquid expanded-condensed transitions occurred. In the phase coexistence region, the condensed state of these compounds formed flowerlike domains (11.1-13.3 Å thick). C12:0 ceramide domains were larger and more densely branched than those of C10:0 ceramide. Both the film thickness and the surface dipole moment of the condensed state increased with ceramide N-acyl chain length. Bending of the sphingosine chain over the N-linked acyl chain in the more asymmetric ceramides can account for the variation of the surface electrostatics, topography, and thickness of the films with the acyl chain mismatch.

Myoblast fusion and inositol phospholipid breakdown: causal relationship or coincidence?

The fusion of embryonic chick myoblasts has been examined in culture. Cells were prepared from 12-day-old chick embryonic breast muscle and cultured for 50 h at a Ca2+ concentration in the medium of 10(-7) M. During this period they attain fusion competence. Addition of 1.4 mM-Ca2+ to these cells elicits rapid fusion. Changes in the metabolism of myoblast phospholipids in response to the raised Ca2+ concentration have been examined. Only the inositol phospholipids are affected. Phosphatidylinositol, phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate are rapidly broken down and 1,2-diacylglycerol and phosphatidic acid are synthesized. Myoblast fusion has also been found to be stimulated by a factor present in chick embryo extract, probably of neuronal origin. A receptor-mediated mechanism for myoblast fusion is proposed. This envisages the polyphosphoinositides acting as a fusion block, either themselves or by their binding to membrane proteins. The inositol phospholipid breakdown could result in a more fluid membrane and the breakdown products 1,2-diacylglycerol and phosphatidic acid, two known fusogens, could stimulate fusion.

Composition-driven surface domain structuring mediated by sphingolipids and membrane-active proteins. Above the nano- but under the micro-scale: mesoscopic biochemical/structural cross-talk in biomembranes

Biomembranes contain a wide variety of lipids and proteins within an essentially two-dimensional structure. The coexistence of such a large number of molecular species causes local tensions that frequently relax into a phase or compositional immiscibility along the lateral and transverse planes of the interface. As a consequence, a substantial microheterogeneity of the surface topography develops and that depends not only on the lipid-protein composition, but also on the lateral and transverse tensions generated as a consequence of molecular interactions. The presence of proteins, and immiscibility among lipids, constitute major perturbing factors for the membrane sculpturing both in terms of its surface topography and dynamics. In this work, we will summarize some recent evidences for the involvement of membrane-associated, both extrinsic and amphitropic, proteins as well as membrane-active phosphohydrolytic enzymes and sphingolipids in driving lateral segregation of phase domains thus determining long-range surface topography.

Biophysics of sphingolipids II. Glycosphingolipids: An assortment of multiple structural information transducers at the membrane surface

Glycosphingolipids are ubiquitous components of animal cell membranes. They are constituted by the basic structure of ceramide with its hydroxyl group linked to single carbohydrates or oligosaccharide chains of different complexity. The combination of the properties of their hydrocarbon moiety with those derived from the variety and complexity of their hydrophilic polar head groups confers to these lipids an extraordinary capacity for molecular-to-supramolecular transduction across the lateral/transverse planes in biomembranes and beyond. In our opinion, most of the advances made over the last decade on the biophysical behavior of glycosphingolipids can be organized into three related aspects of increasing structural complexity: (1) intrinsic codes: local molecular interactions of glycosphingolipids translated into structural self-organization. (2) Surface topography: projection of molecular shape and miscibility of glycosphingolipids into formation of coexisting membrane domains. (3) Beyond the membrane interface: glycosphingolipid as modulators of structural topology, bilayer recombination and surface biocatalysis.

Behavior of GM3 ganglioside in lipid monolayers mimicking rafts or fluid phase in membranes

We studied the interaction of GM3 ganglioside with sphingomyelin (SM) and palmitoyl-oleoyl-phosphatidylcholine (POPC) in Langmuir monolayers mimicking, respectively, raft and fluid phase of a cellular membrane, by surface pressure measurements and fluorescence microscopy. No difference was observed in the behavior of SM-GM3 and POPC-GM3 monolayers. In both cases, a GM3 threshold concentration has been underlined between 20 and 40 mol%. Below this threshold, SM-GM3 and POPC-GM3 monolayers behave ideally, suggesting that GM3 and host lipid would form separated domains. On the contrary, above the threshold, a condensation of monolayers is observed. This could be due to a partial solubilisation of GM3 in host lipid, leading to a change in orientation of GM3 molecules at the air-water interface.

Favorable and unfavorable lateral interactions of ceramide, neutral glycosphingolipids and gangliosides in mixed monolayers

Interactions among four natural neutral sphingolipids (ceramide, glucosyl-ceramide, lactosyl-ceramide and asialo-GM1) and six gangliosides (GM3, GM2, GM1, GD3, GD1a and GT1b) were studied in binary Langmuir monolayers at the air-buffer interface in terms of their molecular packing, compressibility, dipole potential and mixing behavior. The changes of surface organization can be grouped into three sets: (a) binary films of neutral GSLs, and of the latter with ceramide, exhibit thermodynamically unfavorable mixing with mean molecular area expansions and dipole moment hyperpolarization; (b) mixed monolayers of ceramide, or of GlcCer, and gangliosides occur with thermodynamically favorable interactions leading to mean molecular area condensation and depolarisation; (c) binary mixtures of LacCer or Gg4Cer with gangliosides, and all ganglioside species among them, revealed molecular immiscibility characterized by additive mean molecular area and dipole potential, with composition-independent constant collapse pressure. These results disclose basic tendencies of GSLs to molecularly mix or demix, leading to their surface segregation, which may underlay vectorial separation of their specific biosynthetic pathways.

New EPR method for cellular surface characterization

An electron paramagnetic resonance (EPR)-based membrane surface characterization method is presented to detect the properties of the carbohydrate-rich part of membrane surfaces as well as carbohydrate interaction with other membrane constituents and water-soluble molecules. The proposed method relies on the spin-labeling and spectral decomposition based on spectral simulation and optimization with EPRSIM software. In order to increase the sensitivity of characterization to the carbohydrate-rich part of the membrane surface, the sucrose-contrasting approach is introduced. With this method, which was established on model membranes with glycolipids and tested on erythrocyte membrane, we were able to characterize the surface and lipid bilayer lateral heterogeneity. Additionally, some properties of the interaction between glycocalyx and lipid bilayer as well as between glycocalyx and sucrose molecules were determined. The experiments also provided some information about the anchoring and aggregation of the glycosylated molecules. According to the results, some functions of the glycosylated surface are discussed.

Lactosylceramide: effect of acyl chain structure on phase behavior and molecular packing

Lactosylceramide (LacCer) is a pivotal intermediate in the metabolism of higher gangliosides, localizes to sphingolipid-sterol "rafts," and has been implicated in cellular signaling. To provide a fundamental characterization of LacCer phase behavior and intermolecular packing, LacCer containing different saturated (16:0, 18:0, 24:0) or monounsaturated (18:1(Delta9), 24:1(Delta15)) acyl chains were synthesized and studied by differential scanning calorimetry and Langmuir film balance approaches. Compared to related sphingoid- and glycerol-based lipids, LacCers containing saturated acyl chains display relatively high thermotropic and pressure-induced transitions. LacCer monolayer films are less elastic in an in-plane sense than sphingomyelin films, but are somewhat more elastic than galactosylceramide films. Together, these findings indicate that the disaccharide headgroup only marginally disrupts gel phase packing and orients more perpendicular than parallel to the interface. This contrasts the reported behavior of digalactosyldiglycerides with saturated acyl chains. Introducing single cis double bonds into the LacCer acyl chains dramatically lowers the high thermotropic and pressure-induced transitions. Greater reductions occur when cis double bonds are located near the middle of the acyl chains. The results are discussed in terms of how an extended disaccharide headgroup can enhance interactions among naturally abundant LacCers with saturated acyl chains.

Synthesis and Characterization of Oligomaltose-Grafted Lipids with Application to Liposomes

Novel glycolipids, which contain 2 and 15 oligomaltose units and a phosphatidylethanolamine, were synthesized and characterized by FTIR and (1)H-NMR spectroscopies. The well-defined linear structure of the glycolipids was assured by an end-point conjugation strategy using selective oxidation of the reducing end groups of maltose oligosaccharides, followed by aminolysis with distearoylphosphatidylethanolamine. The intermediate acids react selectively with amines to form amide linkages, catalyzed by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide. Conformations of the glycolipids at the air-water interface were proposed based on the film balance measurements. The unique conformations of glycolipids at interfaces may offer advantages over traditional PEO-derived lipids in regard to their applications for sterically stabilizing liposomes. The glycolipids demonstrated the ability for sterically stabilizing liposome dispersions, as determined by turbidity measurements.

Interactions of amyloid beta-protein with various gangliosides in raft-like membranes: importance of GM1 ganglioside-bound form as an endogenous seed for Alzheimer amyloid

GM1 ganglioside-bound amyloid beta-protein (GM1-Abeta), found in brains exhibiting early pathological changes of Alzheimer's disease (AD) plaques, has been suggested to accelerate amyloid fibril formation by acting as a seed. We have previously found using dye-labeled Abeta that Abeta recognizes a GM1 cluster, the formation of which is facilitated by cholesterol [Kakio, A., Nishimoto, S., Yanagisawa, K., Kozutsumi, Y., and Matsuzaki, K. (2001) J. Biol. Chem. 276, 24985-24990]. In this study, we investigated the ganglioside species-specificity in its potency to induce a conformational change of Abeta, by which ganglioside-bound Abeta acts as a seed for Abeta fibrillogenesis, using a major ganglioside occurring in brains (GM1, GD1a, GD1b, and GT1b) in raft-like membranes composed of cholesterol and sphingomyelin. Abeta recognized ganglioside clusters, the density of which increased with the number of sialic acid residues. Interestingly, however, mixing of gangliosides inhibited cluster formation. In contrast, the affinities of the protein for the clusters were similar irrespective of lipid composition and of the order of 10(6) M(-)(1) at 37 degrees C. Abeta underwent a conformational transition from an alpha-helix-rich structure to a beta-sheet-rich structure with the increase in protein density on the membrane. Ganglioside-bound Abeta proteins exhibited seeding abilities for amyloid formation. GM1-Abeta exhibited the strongest seeding potential, especially under beta-sheet-forming conditions. This study suggested that lipid composition including gangliosides and cholesterol strictly controls amyloid formation.

Concerted modulation by myelin basic protein and sulfatide of the activity of phospholipase A2 against phospholipid monolayers

The effect of myelin basic protein (MBP) on the activity of phospholipase A2 (PLA2, EC 3.1.1.4) against monolayers of dilauroylphosphatidylcholine (dlPC) or dilauroylphosphatidic acid (dlPA) containing different proportions of sulfatide (Sulf) and galactocerebroside (GalCer) was investigated. MBP was introduced into the interface by direct spreading as an initial constitutive component of the lipid-protein film or by adsorption and penetration from the subphase into the preformed lipid monolayers. The effect of MBP on PLA2 activity depends on the type of phospholipid and on the proportion of MBP at the interface. At a low mole fraction of MBP, homogeneously mixed lipid-protein monolayers are formed, and the PLA2 activity against dlPC is only slightly modified while the degradation of dlPA is markedly inhibited. This is probably due to favorable charge-charge interactions between dlPA and MBP that interfere with the enzyme action. The PLA2 activity against either phospholipid is increased when the mole fraction of MBP exceeds the proportion at which immiscible surface domains are formed. GalCer has little effect on the modulation by MBP of the phospholipase activity. The effect of Sulf depends on its proportions in relation to MBP. The individual effects of both components balance each other, and a finely tuned modulation is regulated by the interactions of MBP with Sulf or with the phospholipid.

Syntheses and interfacial behaviour of neoglycolipid analogues of glycosyl ceramides

Four glycosyl ceramides analogues having D-galactose or 2-acetamido-2-deoxy-D-glucose moieties linked to enantiomeric lipids have been synthesised to study their interfacial behaviour at the air/water interface. The lipid chains were prepared in two steps by opening 1,2-epoxyhexadecane using Jacobsen kinetic hydrolytic resolution (KHR) followed by an azidosilylation reaction of the diol so obtained. Glycosylation reactions were realised either with 2,3,4,6-tetra-O-benzoyl-alpha-D-galactopyranosyl trichloroacetimidate or 1,3,4,6-tetra-O-acetyl-2-allyloxycarbonylamino-2-deoxy-beta-D-glucopyranose as donors and (2R)- or (2S)-2-azidohexadecanol derivatives as acceptors. Transformation of the azido glycosides into N-acylated products was done by a modified Staudinger reaction in the presence of fatty acyl chlorides. The four neoglycolipids are able to form a condensed monolayer at the air/water interface; their pi-A isotherm diagrams are similar to that described for the natural glycosyl ceramides. The detailed analysis of the isotherms, taking into account the chirality of the lipid chains, allowed to determine the contribution of the different parts of the molecule under the monolayer packing.

Interaction of GM(1) glycolipid in phospholipid monolayers with wheat germ agglutinin: effect of phospholipidic environment and subphase

Mixed monolayers of GM(1) glycolipid and stearoyl-oleoyl-phosphatidylcholine (SOPC) or dipalmitoyl-phosphatidycholine (DPPC) phospholipids were studied by surface pressure measurements. The effects induced by GM(1) on the mean molecular areas of mixtures and DPPC phase transition were followed for GM(1) concentrations ranging from 1 to 20 mol.%. Under our experimental conditions, one main parameter influencing the behavior of phospholipid-GM(1) monolayers is the ionic strength of the subphase. Mixed monolayers are in a more expanded state on buffer than on pure water. This could be due to a change of GM(1) orientation at the interface. The interaction of wheat germ agglutinin (WGA), a lectin recognizing specifically GM(1), with these monolayers was quantified in terms of the Gibbs equation. Specific WGA-GM(1) interactions are clearly reduced in the presence of DPPC as compared with SOPC, probably because of the higher packing density of these monolayers. Phospholipid-GM(1) monolayers could also undergo some rearrangements induced by WGA binding.

Water dynamics in glycosphingolipid aggregates studied by LAURDAN fluorescence

We have characterized the fluorescence properties of 6-dodecanoyl-2-dimethylamine-naphthalene (LAURDAN) in pure interfaces formed by sphingomyelin and 10 chemically related glycosphingolipids (GSLs).1 The GSLs contain neutral and anionic carbohydrate residues in their oligosaccharide chain. These systems were studied at temperatures below, at, or above the main phase transition temperature of the pure lipid aggregates. The extent of solvent dipolar relaxation around the excited fluorescence probe in the GSLs series increases with the magnitude of the glycosphingolipid polar headgroup below the transition temperature. This conclusion is based on LAURDAN's excitation generalized polarization (GPex) and fluorescence lifetime values found in the different interfaces. A linear dependence between the LAURDAN GPex and the intermolecular spacing among the lipid molecules was found for both neutral and anionic lipids in the GSLs series. This relationship was also followed by phospholipids. We conclude that LAURDAN in these lipid aggregates resides in sites containing different amounts of water. The dimension of these sites increases with the size of the GSLs polar headgroup. The GP function reports on the concentration and dynamics of water molecules in these sites. Upon addition of cholesterol to Gg4Cer, the fluorescence behavior of LAURDAN was similar to that of pure cerebrosides and sphingomyelin vesicles. This observation was attributed to a change in the interfacial hydration as well as changes in the shape and size of the Gg4Cer aggregates in the presence of cholesterol. After the addition of cholesterol to gangliosides, the changes in the LAURDAN's spectral parameters decrease progressively as the polar headgroup of these lipids becomes more complex. This finding suggests that the dehydration effect of cholesterol depends strongly on the curvature radius and the extent of hydration of these lipid aggregates. In the gel phase of phrenosine, GalCer, Gg3Cer, sulfatide, and sphingomyelin, the excitation red band (410 nm) of LAURDAN was reduced with respect to that of LAURDAN in the gel phase of pure phospholipids. This observation indicates a local environment that interacts differently with the ground state of LAURDAN in GSLs when compared with LAURDAN in phospholipids.

Lack of effect of Miller Fisher sera/plasmas on transmitter release from PC12 cells

IgG antibodies to GQ1b ganglioside are found in > 90% of patients with the Miller Fisher Syndrome (MFS). MFS sera or IgG preparations have marked effects on neurotransmitter release at the neuromuscular junction, but their mode(s) of action remain unclear. To establish a cell-based system for investigating the mechanism of action of MFS serum preparations, we looked at neurotransmitter release from three cell lines. We failed to demonstrate substantial 14C-acetylcholine release from two motor-neuronal cell lines, VSC4.1 and NSC19, and therefore studied 3H-noradrenaline release from NGF-differentiated PC12 cells, a neural-crest derived catecholaminergic cell line. K(+)-induced release was inhibited by botulinum toxin and basal release was enhanced by alpha-latrotoxin, resembling that at the neuromuscular junction, although K(+)-induced release was dependent on L-type rather than P/Q-type calcium channels. The cells expressed polysialylated gangliosides on the cell surface. Incubation in heat-inactivated or untreated MFS preparations did not, however, affect basal or K(+)-induced release. Thus the PC12 cells do not appear to be sensitive to the effects of serum antibodies from MFS patients.

Oriented 1,2-dimyristoyl-sn-glycero-3-phosphorylcholine/ganglioside membranes: a Fourier transform infrared attenuated total reflection spectroscopic study. Band assignments; orientational, hydrational, and phase behavior; and effects of Ca2+ binding

Fourier transform infrared (FTIR) attenuated total reflection (ATR) spectroscopy was used to elucidate the hydration behavior and molecular order of phospholipid/ganglioside bilayers. We examined dry and hydrated films of the gangliosides GM1, deacetyl-GM1, lyso-GM1, deacetyllyso-GM1, and GM3 and oriented mixed films of these gangliosides with 1,2-dimyristoyl-sn-glycero-3-phosphorylcholine (DMPC) using polarized light. Analysis of the amide I frequencies reveals that the amide groups are involved in intermolecular interactions via hydrogen bonds of varying strengths. The tilt angle of the acyl chains of the lipids in mixed films was determined as a function of ganglioside structure. Deacetylation of the sialic acid in the headgroup has a stronger influence on the tilt angle than the removal of the ganglioside fatty acid. The phase behavior was examined by FTIR ATR spectroscopy and by differential scanning calorimetry (DSC) measurements on lipid suspensions. At the same molar concentration, lyso-gangliosides have less effect on changes of transition temperature compared to the double-chain analogs. Distinct differences in the amide band shapes were observed between mixtures with lyso-gangliosides and normal double-chain gangliosides. Determined from the dicroic ratio RATR, the orientation of the COO- group in all DMPC/ganglioside mixtures was found to be relatively fixed with respect to the membrane normal. In 4:1 mixtures of DMPC with GM1 and deacetyl-GM1, the binding of Ca2+ leads to a slight decrease in chain tilt in the gel phase, probably caused by a dehydration of the membrane-water interface. In mixtures of DMPC with GM3 and deacetyl-lyso-GM1, a slight increase in chain tilt is observed. The chain tilt in DMPC/lyso-GM1 mixtures is unchanged. Analysis of the COO- band reveals that Ca2+ does not bind to the carboxylate group of the sialic acid of GM1 and deacetyl-GM1, the mixtures in which a decrease in chain tilt was observed. Binding to the sialic acid was only observed for mixtures of DMPC with GM3, lyso-GM1, and deacetyl-lyso-GM1. Ca2+ obviously accumulates at the bilayer-water interface and leads to partial dehydration of the headgroup region in the gel as well as in the liquid-crystalline phase. This can be concluded from the changes in the amide I band shapes. With the exception of DMPC/deacetyl-GM1, the effects on the ester C==O bands are small. The addition of Ca2+ has minor effects on the phase behavior, with the exception of the DMPC/GM1 mixture.

Properties of ganglioside GM1 in phosphatidylcholine bilayer membranes

Gangliosides have been shown to function as cell surface receptors, as well as participating in cell growth, differentiation, and transformation. In spite of their multiple biological functions, relatively little is known about their structure and physical properties in membrane systems. The thermotropic and structural properties of ganglioside GM1 alone and in a binary system with 1,2-dipalmitoyl phosphatidylcholine (DPPC) have been investigated by differential scanning calorimetry (DSC) and x-ray diffraction. By DSC hydrated GM1 undergoes a broad endothermic transition TM = 26 degrees C (delta H = 1.7 kcal/mol GM1). X-ray diffraction below (-2 degrees C) and above (51 degrees C) this transition indicates a micellar structure with changes occurring only in the wide angle region of the diffraction pattern (relatively sharp reflection at 1/4.12 A-1 at -2 degrees C; more diffuse reflection at 1/4.41 A-1 at 51 degrees C). In hydrated binary mixtures with DPPC, incorporation of GM1 (0-30 mol%; zone 1) decreases the enthalpy of the DPPC pretransition at low molar compositions while increasing the TM of both the pre- and main transitions (limiting values, 39 and 44 degrees C, respectively). X-ray diffraction studies indicate the presence of a single bilayer gel phase in zone 1 that can undergo chain melting to an L alpha bilayer phase. A detailed hydration study of GM1 (5.7 mol %)/DPPC indicated a conversion of the DPPC bilayer gel phase to an infinite swelling system in zone 1 due to the presence of the negatively charged sialic acid moiety of GM1. At 30-61 mol % GM1 (zone 2), two calorimetric transitions are observed at 44 and 47 degrees C, suggesting the presence of two phases. The lower transition reflects the bilayer gel --> L alpha transition (zone 1), whereas the upper transition appears to be a consequence of the formation of a nonbilayer, micellar or hexagonal phase, although the structure of this phase has not been defined by x-ray diffraction. At > 61 mol % GM1 (zone 3) the calorimetric and phase behavior is dominated by the micelle-forming properties of GM1; the presence of mixed GM1/DPPC micellar phases is predicted.

Structure and properties of N-palmitoleoylgalactosylsphingosine (cerebroside)

Differential scanning calorimetry (DSC) and X-ray diffraction have been used to study the structure and properties of N-palmitoleoylgalactosylsphingosine (NPoGS; 16:1 galactocerebroside). DSC of fully hydrated NPoGS shows a complex pattern of three endothermic transitions at 35, 39 and 53 degrees C. Using a combination of thermal protocols (varying heating/cooling rates, incubation at different temperatures, etc.), the three ordered chain (gel) phases responsible for the transitions have been isolated; transition I (Tm = 35 degrees C; delta H(I) = 6.3 kcal/mol), transition II (Tm = 39 degrees C; delta HII = 8.6 kcal/mol), and transition III (Tm = 53 degrees C; delta HIII = 12.8 kcal/mol). The gel phases do not interconvert but rather form independently following cooling from the melted chain phase. X-ray diffraction data of the three isolated phases confirm that they all are bilayer structures with different bilayer periodicities (LI, 50.7 A; LII, 51.7 A; LIII = 49.2 A) and different chain packing modes. The LI, LII, and LIII bilayer phases each melt independently to the melted chain L alpha phase. Comparisons with other cerebrosides make it clear that alterations in chain length and chain unsaturation markedly affect the thermotropic behavior of cerebrosides and the metastable and stable phases they are able to form. As with phospholipids, introduction of cis-unsaturation into the N-acyl chain reduces both the chain melting temperature and enthalpy.

Oligosaccharide behavior of complex natural glycosphingolipids in multicomponent model membranes

Wideline 2H NMR of model membranes was used to consider the molecular consequences of factors often suggested as modulators of complex glycosphingolipid oligosaccharide arrangement and motional characteristics at cell surfaces. GM1, asialo-GM1, and globoside were studied as examples of plasma membrane recognition sites. The experimental approach involved substitution of deuterons (D) for protons at specific locations within the carbohydrate chains. Deuterated glycolipids were then dispersed at 7-10 mol% in unsonicated bilayers of 1-palmitoyl-2-oleoylphosphatidylcholine. Factors tested for their significance to carbohydrate chain conformation and dynamics included glycolipid natural alkyl and acyl chain variability, membrane fluidity, and the presence of cholesterol and a charged sugar residue (neuraminic acid). Effects of Ca2+ and membrane-associated protein were briefly considered. Two distinct strategies were employed in substituting deuterons for selected protons of carbohydrate residues. Neither approach necessitated alteration of the glycolipid natural fatty acid composition. (i) Protons of the exocyclic hydroxymethyl group on the terminal Gal residue of GM1 and asialo-GM1, and on the terminal N-acetylgalactosamine (GalNAc) residue of globoside, were replaced with deuterium (producing -CDHOH) by an enzymatic oxidation/reduction cycle. This represents the first application of such an approach to deuteration of complex neutral glycolipids. Spectral results were compared to those obtained for the similarly-deuterated monoglycosyl lipid, galactosylceramide (GalCer), with natural fatty acid composition. Efficacy of this labeling method may in principle be influenced by structural variations within a given glycolipid family. Also, asymmetric rotation of the deuterated group made it less attractive than the second method for relating spectral features to receptor geometry. (ii) A general synthetic, nonenzymatic method was investigated for replacing amino sugar N-acetyl groups with deuterated acetate (-COCD3). The acetate group of the GalNAc residue of globoside, GM1, and asialo-GM1, as well as that on neuraminic acid in GM1, was replaced with -COCD3. This second method afforded better signal-to-noise--an important consideration for 2H NMR. The NMR technique employed had the potential for detecting changes of as little as 10% in oligosaccharide orientation or motional order. Each glycolipid demonstrated clear evidence of preferred average oligosaccharide conformations in all (fluid) membrane environments examined. The most striking observation was that, in fluid matrices, conformation and motional order of the complex oligosaccharide chains were only modestly influenced by factors tested, including natural variation in the glycolipid hydrocarbon chains, membrane fluidity, temperature, and the presence of cholesterol or the N-acetylneuraminic acid (NeuAc) residue on GM1.(ABSTRACT TRUNCATED AT 400 WORDS)

Modulation by gangliosides of the lamellar-inverted micelle (hexagonal II) phase transition in mixtures containing phosphatidylethanolamine and dioleoylglycerol

We studied the effect of gangliosides GD1a and GM1 on the lamellar-to-hexagonal II phase transition of mixtures of dioleoylphosphatidylethanolamine/dioleoylphosphatidyl choline, 3:1, and of transphosphatidylated phosphatidylethanolamine with dioleoylglycerol by high-sensitivity differential scanning calorimetry, 31P-NMR, and pyrene fluorescence of a phosphatidylcholine probe. Gangliosides had a dual effect. Below 1 mol % ganglioside the hexagonal II phase transition was affected but still occurred at lower temperature than in the absence of gangliosides. The presence of between 1 and 2 mol % gangliosides increased the temperature for formation of the hexagonal II phase and progressively decreased its cooperativity. Above 3 mol % gangliosides totally inhibited the formation of both the temperature-induced and composition-induced hexagonal phase, probably by opposing the geometric distortions necessary for the inverted micellar structures.

Exposure to galactose oxidase of GM1 ganglioside molecular species embedded into phospholipid vesicles

The exposure of GM1 molecular species present in the native ganglioside, carrying C18:1 or C20:1 long-chain bases (LCB), to Dactylium dendroides galactose oxidase was studied. When native GM1 (49.3% C18:1 and 50.7% C20:1 LCB, respectively), was inserted in dipalmitoylphosphatidylcholine vesicles and partially oxidized (10%), the proportion of C18:1 and C20:1 species in the oxidized GM1 was 59.6% and 40.4%, respectively, suggesting a preferential action of the enzyme on the shorter species. The Vmax of the enzyme was higher on C18:1 GM1 than on C20:1 GM1. The molecular species were affected without any preference after partial (10%) oxidation of GM1 incorporated in egg phosphatidylcholine vesicles or in micellar form. These data indicate that the exposure of the terminal galactose moiety of GM1 ganglioside to galactose oxidase is affected by the ganglioside ceramide composition as well as the phospholipid environment, that presumably determine the distribution (molecular dispersion, segregation) of the ganglioside within the membrane.

[Brain gangliosides and memory formation]

It is generally accepted that the process of molecular facilitation (= Bahnung) of neuronal circuits by means of stabilization of synaptic contacts represents the structural basis for memory formation. On the basis of physiological, electron microscopic, biochemical, and physicochemical data, a concept is presented speaking in favor of the idea that interactions between brain gangliosides (= amphiphilic sialic acid-containing glycosphingolipids with peculiar physicochemical properties), calcium, and functional membraneous proteins (ion channels, ion pumps, receptors, kinases) play a crucial modulatory role in the transmission and storage of information.

Molecular parameters of semisynthetic derivatives of gangliosides and sphingosine in monolayers at the air-water interface

The molecular parameters (molecular area, surface potential, collapse pressure, dipole moment contributions) of semisynthetic derivatives of ganglioside GM1 and of sphingosine were studied in lipid monolayers at the air-NaCl (145 mM, pH 5.6) interface at 22 +/- 0.3 degrees C. The chemical modifications included alterations of the fatty acyl chain moiety linked to the 2-amino position of the sphingosine (Sph) base. The compounds studied were PKS-1 (N-acetyl Sph), PKS-2 (N-chloroacetyl Sph), PKS-3 (N-dichloroacetyl Sph), PKS-4 (N-trichloroacetyl Sph), Lyso-GM1 (ganglioside GM1 lacking the N-linked fatty acyl chain and the N-acetyl group on the sialic acid), Liga-4 (N-acetyl, lyso[NeuAc]GM1) and Liga-20 (N-dichloroacetyl, lyso[NeuAc]GM1). Relatively small modifications of the chemical structure of sphingolipids introduce dramatic consequences on their surface molecular properties. The absence of the long chain fatty acyl moiety and of the N-acetyl group on the neuraminic acid in Lyso-GM1 leads to a more condensed behavior and to an increase of the collapse pressure compared with GM1. The acetylation or chloroacetylation at the 2-amino position in Liga-4 and Liga-20 induce an expansion of the surface pressure-area isotherm and a decrease of the collapse pressure. The limiting molecular areas of GM1 derivatives, taken at the collapse pressure point, are consistent with the oligosaccharide chain being oriented approximately perpendicularly to the interface. Sphingosine shows a liquid expanded isotherm. The acetylation and successive chlorination of the acetyl residue at the 2-amino position of Sph cause a progressive increase in the limiting molecular area. The variation of the resultant dipole moment under compression, calculated from the surface potential values, suggests the reorientation of selective groups within these molecules that depend on the degree of intermolecular packing. Thermodynamic-geometric correlations on the basis of the molecular parameters of these derivatives suggest that small alterations of the substituent group at the 2-amino position of Sph could have large and amplified consequences on the type, curvature and stability of the possible self-aggregated structure that these lipids may form in aqueous medium.

The influence of neuraminidase treatment on tracheal smooth muscle contraction

To examine the role of sialic acid in the respiratory tract, the influence of neuraminidase from Clostridium perfringens was investigated on contractions of isolated guinea-pig and rat trachea and on histamine release from guinea-pig lung tissue. Treatment with 2.0 units/ml of neuraminidase at 37 degrees C and pH 7.4 for 30 min caused an approximately 60% removal of total N-acetylneuraminic acid, a representative sialic acid, from muscle from guinea-pig and rat trachea. Neuraminidase concentration dependently induced histamine release from guinea-pig chopped lung tissue, but has no effect on contractions produced by acetylcholine, histamine and 5-hydroxytryptamine. Pretreatment with 2.0 units/ml of neuraminidase inhibited the contraction induced by antigen (ovalbumin) or compound 48/80. These findings suggest, at least in part, that sialic acids sensitive to neuraminidase are involved in the regulation of histamine release but not tracheal contraction.

Glycosphingolipid phase behaviour in unsaturated phosphatidylcholine bilayers: a 2H-NMR study

2H-NMR was employed to consider the arrangement of a glycosphingolipid, N-(lignoceroyl-d47)galactosylceramide, in bilayers of the mono-unsaturated phospholipid, 1-stearoyl-2-oleoylphosphatidylcholine. The deuterated glycolipid prepared by partial synthesis was incorporated at concentrations ranging from 5 mol% to 53 mol% into unsonicated liposomes, and its spectra were recorded from +76 degrees C to -10 degrees C. First spectral moments were plotted as a function of temperature for each sample composition and, along with inspection of the spectra, were employed to infer a phase diagram describing glycolipid behaviour in the unsaturated phospholipid host matrix. It was possible to refine the result using 2H-NMR difference spectroscopy. The phase diagram obtained was indicative of peritectic behaviour. At glycolipid concentrations exceeding about 20 mol% there was considerable tendency to glycolipid phase separation--as indicated by coexistence of fluid phospholipid-enriched and gel phase glycolipid-enriched domains over a wide range of temperatures, and by coexistence of distinct ordered phase domains at lower temperature. In contrast, at lower glycolipid concentrations reflective of many biological membranes, the lipid components were miscible in both the liquid crystal and gel phases, with only a narrow temperature range of fluid and ordered phase coexistence. For the fluid phase at low glycolipid concentrations, spectra of the deuterated glycolipid 24-carbon fatty acid suggest that orientational order is low for a number of methylene groups near the methyl end of the chain.

Glycolipid depletion using a ceramide analogue (PDMP) alters growth, adhesion, and membrane lipid organization in human A431 cells

Glycolipids were depleted from the membranes of human A431 cells using 1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP), an inhibitor of glucosylceramide synthetase. After 6 days of culture in the presence of 5 microM D-threo-PDMP, glycolipid content was reduced to approximately 5% of control levels. By contrast, synthesis per cell of phosphatidylcholine, sphingomyelin, triglycerides, and glycoprotein was relatively unchanged in PDMP-treated cells. In parallel with glycolipid depletion, PDMP-treated cells exhibited a rapid loss of epithelial cell morphology, a reduced rate of cell growth, and inhibition of cell-substrate adhesion. The effects of D-threo-PDMP on cell morphology and substrate adhesion were blocked by exogenous GM3 addition and were not observed with L-threo-PDMP (a relatively inactive enantiomer). Fluorescence photobleaching and recovery (FPR) was used to investigate the hypothesis that glycolipids influence cell behavior, in part, by changing the diffusion characteristics of membrane proteins and lipids. Diffusion coefficients and mobile fractions of two integral membrane proteins, the EGF receptor and a class I MHC antigen, did not differ significantly between control and PDMP-treated cells. Diffusion coefficients of lipid probes, NBD-PC and fluorescent GM1 ganglioside, were similarly unaffected by glycolipid depletion. However, lipid probes did show a significant increase in mobile fraction (the fraction of lipids that are free to diffuse) in PDMP-treated cells. This increase was blocked by culturing cells in the presence of exogenous GM3 ganglioside. The results suggest that glycolipids play a role in the formation of lipid domains in A431 cell membranes. Glycolipid-mediated changes in membrane lipid organization may influence receptor activation and transmembrane signaling, leading to changes in cell growth, morphology, and adhesion.

Thermotropic phase properties of the hydroxyceramide/cholesterol system

The interaction of cholesterol with ceramides containing alpha-hydroxy fatty acyl chains (hydroxyceramides) has been studied as a foundation for characterizing the lipid bilayers of the stratum corneum. A relatively large quantity of cerebrosides was obtained from bovine brain and converted to ceramides through removal of the carbohydrate side chain. The ceramides were separated based on the absence or presence of hydroxy fatty acyl chains. The lyophilized hydroxyceramides showed a broad melting region at 92 degrees C. Hydroxyceramides dispersed in water produced a relatively narrow, thermotropic transition at 75 degrees C. The effect of cholesterol on this thermotropic phase transition of hydroxyceramides was determined by differential scanning calorimetry. With respect to the main transition, cholesterol caused a broadening of the phase transition at relatively low levels as well as a decrease in the peak transition temperature. The presence of cholesterol at levels in excess of 7 wt% gave rise to an additional low-temperature transition at 55 degrees C. Upon immediate rescanning, this transition was exothermic, but with increasing incubation time the area under the excess heat capacity curve as a function of temperature became smaller. After two days or more, the transition observed was endothermic. At cholesterol levels between 40 and 50 wt%, multiple peaks were observed. From comparisons with related systems, the cooperative thermal transitions of hydroxyceramides with cholesterol are suggested to result from changes in hydrogen bonding or be due to phase separation. The composition of isolated brain ceramides is being compared with that reported for the stratum corneum.

Interaction of ganglioside-containing planar bilayers with serotonin and inorganic cations

The binding of serotonin and inorganic cations K+, Na+, Ca2+, Mg2+ to planar bilayers formed from mixtures of phosphatidylcholine and mono-, di- and trisialogangliosides was studied by the potentiodynamic and nonactin-induced potassium conductivity method. The theoretical analysis of the results obtained was made taking into account (1) protrusion of the ganglioside charges from the membrane surface and (2) simultaneous adsorption of ions on the bilayer surface and on the ganglioside charges protruding into the solution. It was shown that there was no specific binding of K+ and Na+. The binding constants for Ca2+, Mg2+ were determined. These constants for all the gangliosides studied were equal to 500 M-1. The determined binding constants of serotonin to various gangliosides diminish in the following order: GD3 greater than GT1b greater than GD1a greater than GM1.

Modulation of phospholipase A2 activity by neutral and anionic glycosphingolipids in monolayers

The effect of neutral (galactocerebroside and asialo-ganglioside GM1) or anionic (sulphatide and gangliosides GM1, GD1a and GT1b) glycosphingolipids on the activity of phospholipase A2 from pig pancreas was studied in mixed monolayers of dilauroyl phosphatidylcholine with the glycosphingolipids in different molar fractions at various constant surface pressures. The activity of the enzyme depends on the proportion and type of glycosphingolipid in the interface. Sulphatide activates the enzyme at all proportions, whereas galactocerebroside shows inhibition or activation depending on its proportion in the film. Asialo-ganglioside GM1 and gangliosides GM1, GD1a and GT1b can strongly inhibit the enzyme at relatively low molar fractions in the film in the following order: asialo-ganglioside GM1 less than ganglioside GM1 less than ganglioside GT1b less than ganglioside GD1a. The changes of activity are not due to a direct action of the lipids on the active centre or interfacial recognition region of the enzyme.

Effect of chain unsaturation on the structure and thermotropic properties of galactocerebrosides

Differential scanning calorimetry (DSC) and x-ray diffraction have been used to study the effect of increasing chain-unsaturation on the structure and properties of the hydrated cerebrosides N-stearoyl, -oleoyl, and -linoleoyl galactosylsphingosine (NSGS, NOGS, and NLnGS, respectively). DSC of hydrated (70 wt% water) NSGS shows an endothermic transition at 85 degrees C (delta H = 18.0 kcal/mol NSGS) and a broad exothermic transition at 40-60 degrees C, the latter being dependent upon the previous cooling rate. X-Ray diffraction patterns recorded at 21, 61, and 86 degrees C provide evidence for interconversions between metastable and stable crystalline NSGS bilayer phases. The properties of the unsaturated-chain cerebrosides are more complex. Hydrated NOGS shows a single endothermic transition at 44.8 degrees C (delta H = 11.5 kcal/mol NOGS). However, incubation of NOGS at 49 degrees C for 24 h results in a second transition at 55.5 degrees C. By cycling NOGS between 0 and 49 degrees C complete conversion into this higher melting phase (delta H = 12.1 kcal/mol NOGS) is achieved. X-ray diffraction confirms a bilayer phase at all temperatures and delineates the conversions between a crystalline phase at 21 degrees C (bilayer period d = 56.5A), a second crystalline phase at 47 degrees C (d = 69.9A), and a liquid crystalline phase at 59 degrees C (d = 52.0A). The more unsaturated NLnGS shows two transitions, a sharp transition at 28 degrees C (delta H = 8.0 kcal/mol NLGS) and a broad, low-enthalpy transition at 42 degrees C (delta H = 0.4 kcal/mol NLGS). Again, incubation between the two transitions leads to a single transition at 44 degrees C (delta H = 9.3 kcal/mol NLGS). X-ray diffraction demonstrates conversions between two crystalline bilayer phases (d = 55.2A and d = 68.4A), and a liquid crystalline bilayer phase (d = 51.8A). Thus, increased unsaturation in the amide-linked fatty acyl chain of cerebrosides results in decreased chain-melting temperatures (NSGS greater than NOGS greater than NLnGS) and has marked effects on their structural properties.

Thermodynamic-geometric correlations for the morphology of self-assembled structures of glycosphingolipids and their mixtures with dipalmitoylphosphatidylcholine

The morphology of aqueous dispersions of five neutral glycosphingolipids (GalCer, GlcCer, LacCer, asialo-GM2, asialo-GM1), sulfatide, and five gangliosides (GM3, GM2, GM1, GD1a and GT1b) and their mixtures with dipalmitoylphosphatidylcholine was studied by negative staining electron microscopy. The morphological features are interpreted on the basis of thermodynamic and geometric constraints previously studied in these systems (Maggio, B (1985) Biochim. Biophys. Acta 815, 245-258). The correlation between the theoretical predictions and the experimental findings are in reasonable agreement. Small changes in the molecular parameters of the individual glycosphingolipids or in their proportion in mixtures with dipalmitoylphosphatidylcholine bring about remarkable variations on the type of structure formed, its radius of curvature and thermodynamic stability.

Interaction of 1-anilinonaphthalene 8-sulfonic acid with interfaces containing cerebrosides, sulfatides and gangliosides

The fluorescence lifetime, quantum yield and emission spectra of 1-anilinonaphthalene 8-sulfonic acid (ANS) associated with interfaces of pure dipalmitoylphosphatidylcholine or its mixtures with phosphatidylserine, galactosylceramide, sulfatide or gangliosides GM1 and GD1a were studied at low and high ionic strength. Modification of the molecular organization of the lipid interfaces in the presence of the probe was also studied with mixed lipid monolayers. ANS has little affect on the intermolecular packing of the lipids but influences their surface potential, consistent with a location of ANS in the polar head group region of the interface. ANS senses a more polar microenvironment when associated with interfaces containing anionic glycosphingolipids at low ionic strength but, except for interfaces containing phosphatidylserine, it detects approximately the same polarity for neutral or anionic interfaces in 0.25 M NaCl.

Ganglioside metabolism in the hippocampus after septal lesion in rats

The changes in ganglioside composition and metabolism of deafferentiated rat hippocampus were estimated after septal lesion. A significant decrease in total ganglioside concentration was found 7 days after the lesion. The reduced level of total gangliosides persisted at 17 and 25 days. Relative increase in the proportion of GD1b and GX (O-acetylated GT1b) and decrease in GM1 were found in hippocampus only at 25 days post-lesion. The incorporation of 3H-N-acetylmannoseamine into gangliosides was examined in rats whose hippocampi were lesioned 25 days prior to radioprecursor injection. Differences in the labeling pattern of total and individual gangliosides were found. Increases in the label in GM1, GD3, and GD1a and decreases in GT1b and GQ1b were found 10 hr after isotope injection. However, decreases in the specific activity of all gangliosides except GT1b and GQ1b were observed 24 hr after 3H-N-acetylomannosamine injection, suggesting the activated turnover of gangliosides in postlesioned hippocampus. The significance of these changes has been discussed in terms of cellular damage and repair in the hippocampal tissue.