Novel ceramides from the fungus Lactarium volemus

Two novel ceramides, lactariamides A (N-2'-hydroxytetracosanoyl-2-amino-3,4-epoxyoctadecan-1-ol (1)) and B ((4E,8E)-N-2'-hydroxyoctadecanoyl-2-amino-9-methyl-4,8-octadecadine-1,3-diol (2)), were isolated from the fungus Lactarium volemus, together with a known compound, cerebroside D (3). Their structures were determined on the basis of chemical evidence and spectral methods.

Genesis of human cerebrospinal fluid

Analysis of two sets of steady-state data on bromide ion in the serum and cerebrospinal fluid of one human subject and of recently published data on the entry of bromide and sodium ions into human cerebrospinal fluid suggests that bromide is secreted out of the bulk of the cerebrospinal fluid, not excluded from it at a source, and that the secretory activity reaches a maximum at high concentrations of bromide ion.

Submitted on August 25, 1958

STABILITY OF THE MYELIN MEMBRANE

The hypothetical questions which were asked earlier may now be answered as follows. Myelin lipids do possess characteristics which could lead to a tightly organized, closely packed, highly stable membrane structure, while lipids in adjacent neurons and glial cells do possess characteristics which could give rise to a more loosely organized, less stable membrane structure. The greater degree of metabolic inertness of myelin lipids may be explained on this basis. The stability of myelin itself may also be based largely on the intermolecular cohesion between lipid molecules, since the lipid content of myelin is extraordinarily high. Physiological and clinical studies tend to support the concept that a surfeit of polyunsaturated lipids or a deficiency of long-chain sphingolipids can result in a more easily disrupted membrane. The most important prediction to be drawn from these speculations is that myelin may be rendered unstable in disease if its lipid composition is altered so that higher proportions of lipids containing polyunsaturated fatty acids and lower proportions of lipids containing very-long-chain fatty acids are present.

THE ISOLATION AND PARTIAL CHARACTERIZATION OF THE GLYCOLIPIDS OF BP8/C3H ASCITES-SARCOMA CELLS

1. The total lipid was extracted from BP8/C3H ascites-sarcoma cells with acetone, light petroleum, pyridine and chloroform-methanol successively. Each extract was treated with mild alkali. The alkali-stable lipids from the pyridine and chloroform-methanol extracts, which included the glycolipids, were fractionated on silicic acid and silica gel G columns. 2. The total yield of glycolipid was about 60 mg./100 g. dry wt. of tumour cells, about 0.4% of the total lipid. Four classes of glycolipid were isolated and characterized as ceramide monohexoside (G1), ceramide dihexoside (G2), ceramide trihexoside (G3) and ceramide hexosaminyltrihexoside (G4). 3. G1, G2, G3 and G4 constituted 55, 21, 9 and 15% of the total glycolipid respectively. 4. G1 was a mixture of ceramide glucoside (70%) and ceramide galactoside. 5. The general structures of the oligosaccharide moieties of G2, G3 and G4 were elucidated by partial acid hydrolysis of the glycolipids with water-soluble polystyrenesulphonic acid. G2 was mostly ceramidelactoside with about 10% of ceramide galactosylgalactoside. G3 and G4 were probably a ceramide digalactosylglucoside and a ceramide N-acetylgalactosaminylgalactosylgalactosylglucoside respectively. 6. The fatty acid compositions of the glycolipids were very similar; lignoceric acid and nervonic acid were the major components and all contained monohydroxy acids in proportions varying from 10 to 25% of the total acids.

Aggregation of acidic lipid vesicles by myelin basic protein: dependence on potassium concentration

In the compacted multilayered myelin sheath of the central nervous system, myelin basic protein (MBP) is thought to be responsible for adhesion of the intracellular surfaces by electrostatic interactions with acidic lipids. Noncompacted regions of myelin containing cytosol exist and can take up potassium released into the extracellular fluid after the axonal action potential. Therefore, the effect of K+ concentration on the ability of MBP to aggregate large unilamellar vesicles (LUVs) containing phosphatidylcholine (PC) and 10-20% acidic lipid was investigated. At MBP to lipid ratios where there was an excess of acidic lipid, physiological increases in K+ concentration up to about 100 mM greatly increased MBP-mediated aggregation of the LUVs by shielding the negative charge on the vesicle surface. Thus, changes in K+ concentration during the axonal action potential could regulate MBP-mediated adhesion of the intracellular myelin surfaces of noncompacted regions of myelin such as the paranodal loops. It could thus regulate the volume of these cytosolic regions, allowing MBP to have a dynamic function in myelin. Concentrations of K+ above 150 mM caused dissociation of MBP from LUVs containing PC and a single acidic lipid. LUVs containing the lipid composition estimated to be characteristic of the cytoplasmic leaflet of myelin (Cyt.-LUVs) were found to interact uniquely with MBP, resulting in greater aggregation, greater sensitivity to K+ concentration, and resistance to dissociation at high K+ concentrations. The latter suggested that electrostatic interactions were not the only force involved in binding of MBP to the Cyt.-LUVs. Hydrogen bonding of the protein to the lipid head groups and hydrophobic interactions due to penetration of hydrophobic amino acid side chains into the bilayer could also occur. The greater involvement of hydrophobic interactions of MBP with Cyt.-LUVs compared to PC/acidic lipid LUVs was confirmed from greater labeling of MBP bound to Cyt.-LUVs by the hydrophobic photolabeled TID. Cholesterol and phosphatidylethanolamine together were found to be responsible for the greater MBP-mediated aggregation of Cyt.-LUVs and the greater TID labeling of MBP bound to Cyt.-LUVs compared to PC/acidic lipid LUVs. Thus, the lipid composition of the intracellular surface of myelin is well suited to allow MBP to mediate adhesion of apposing intracellular membranes and to respond in a dynamic way in some regions of myelin, such as the paranodal loops, to changes in K+ concentration resulting from nerve conduction.

Do the long fatty acid chains of sphingolipids interdigitate across the center of a bilayer of shorter chain symmetric phospholipids?

Novel cerebroside sulfate (CBS) spin labels containing long chain C24 or C26 fatty acids with a nitroxide spin label on the 22nd carbon were synthesized and used to investigate the ability of the long fatty acid chains of glycosphingolipids to interdigitate across the center of a non-interdigitated bilayer of phospholipids formed of symmetric saturated or unsaturated shorter fatty acid chain species, in the presence or absence of cholesterol. The motion of these long chain spin labels incorporated at 1 mole% in dimyristoylphosphatidylcholine (diC14-PC), dipalmitoylphosphatidylcholine (diC16-PC), distearoylphosphatidylcholine (diC18-PC), dibehenoylphosphatidylcholine (diC22-PC), spingomyelin (SM), 1-stearoyl-2-oleoylphosphatidylcholine (18:0.18:1-PC), and dimyristoylphosphatidylethanolamine (diC14-PE) was compared to that of CBS spin labels containing stearic acid spin labeled at the 5th carbon and at the 16th carbon. The results indicated that the C26 chain is interdigitated in the gel phase of diC14-PC, diC16-PC, SM, and possibly diC18-PC, but not diC14-PE, and the C24 chain may interdigitate in diC14-PC but not in the other phospholipids. Thus in order to interdigitate across the center of gel phase bilayers, the long acyl chain of the sphingolipid probably must be long enough to nearly span the phospholipid bilayer. The inability to interdigitate in diC14-PE is likely due to the close packing of this lipid in the gel phase. The C26 chain may also be interdigitated in these lipids in the presence of cholesterol at low temperatures. However, at physiological temperatures in the presence of cholesterol and in the liquid-crystalline phase of all the lipids, the results indicate that the long acyl chain of the glycosphingolipid is not interdigitated, but rather must terminate at the bilayer center. This may force the carbohydrate headgroup of the glycosphingolipid farther above the bilayer surface, allowing it to be recognized better by various carbohydrate binding ligands and proteins.

The effect of hydrogen bonds on the conformation of glycosphingolipids. Methylated and unmethylated cerebroside studied by X-ray single crystal analysis and model calculations

The conformation and molecular packing of permethylated beta-D-galactosyl-N-octadecanoyl-D-spingosine (cerebroside) was determined by X-ray single crystal analysis at 185 K (R = 0.16). The lipid crystallizes in the orthorhombic space group P2(1)2(1)2(1) with the unit cell dimensions a = 8.03, b = 7.04 and c = 88.10 A. The four molecules in the unit cell pack in a bilayer arrangement with tilting (48 degrees) hydrocarbon chains. The direction of the chain tilt alternates in the two bilayer halves and in adjacent bilayers. In order to define the effect of hydrogen bonds on the molecular conformation the structural features of the permethylated cerebroside are compared with that of unsubstituted cerebroside (I. Pascher and S. Sundell (1977) Chem. Phys. Lipids 20, 179). It is shown that methylation of the hydrogen donor groups does not affect the conformation of the ceramide part. However, by abolishing the intramolecular hydrogen bond between the amide N--H group and the glycosidic oxygen the galactose ring changes its orientation from layer-parallel to layer-perpendicular. Calculations using molecular mechanics, MM2(87), show that in natural cerebroside the intramolecular hydrogen bond stabilizes the theta 1 = -syn-clinal conformation about the C(1)--C(2) sphingosine bond by 2-2.5 kcal/mol compared to other staggered conformations. The significance of the L shape of the native cerebroside, making both the carbohydrate and polar ceramide groups accessible as a binding epitope in recognition processes, is discussed.

Anisotropic 2H NMR spin-lattice relaxation in L alpha-phase cerebroside bilayers

A series of 2H NMR inversion recovery experiments in the L alpha phase of the cerebroside N-palmitoylgalactosylsphingosine (NPGS) have been performed. In these liquid crystalline lipid bilayers we have observed substantial anisotropy in the spin-lattice relaxation of the CD2 groups in the acyl chains. The form and magnitude of the anisotropy varies with position in the chain, being positive in the upper region, decreasing to zero at the 4-position, and reversing sign at the lower chain positions. It is also shown that addition of cholesterol to the bilayer results in profound changes in the anisotropy. These observations are accounted for by a simple motional model of discrete hops among nine sites, which result from the coupling of two modes of motion--long-axis rotational diffusion and gauche-trans isomerization. This model is employed in quantitative simulations of the spectral line shapes and permits determination of site populations and motional rates. These results, plus preliminary results in sphingomyelin and lecithin bilayers, illustrate the utility of T1 anisotropy measurements as a probe of dynamics in L alpha-phase bilayers.

Interaction and fusion of unilamellar vesicles containing cerebrosides and sulfatides induced by myelin basic protein

The effects of myelin basic protein on the aggregation, lipid bilayer merging, intercommunication of aqueous compartments and leakage of small unilamellar vesicles of egg phosphatidylcholine containing different proportions of galactocerebroside and sulfatide were investigated. This was performed employing light scattering, absorbance changes and fluorescence assays (resonance energy transfer, Terbium/dipicolinic acid assay and carboxyfluorescein release). The apposition of membranes rapidly induced by myelin basic protein is enhanced by sulfatide but reduced by galactocerebroside compared to vesicles of egg phosphatidylcholine alone. On the other hand, the presence of either glycosphingolipid in the membrane interferes with the induction by myelin basic protein of lipid bilayer merging, subsequent fusion and changes of the membrane permeability. Our results support an important modulation by sulfatide and galactocerebroside on the interactions among membranes induced by myelin basic protein, depending on the relative proportions of the glycosphingolipids and phosphatidylcholine.

A Raman and FTIR analysis

Perturbations induced by a toxic lectin (ricin) on lipid organisation of model membranes prepared with DPPC and DPPC-cerebrosides mixtures have been analysed by Raman and infrared spectroscopy, two powerful and non-invasive methods. Our approach involves the observation of changes in the vibrational spectra of liquid multilayers in the PO2-, C = O and CH2 spectral regions for two lipid:ricin molar ratios (225:1, 75:1). The interfacial and polar regions of the multilayers, analysed by FTIR, appear to be perturbed by the protein. With both kinds of membranes, ricin mainly perturbs the C = O ester groups of the sn-2 acylchain of DPPC. In the PO2- stretching region, the frequency shifts are correlated with changes in polar group hydration. In the hydrophobic core of the multilayer membrane studied by Raman spectroscopy, the interaction of ricin is associated with changes in lipid packing. These perturbations depend upon the lipid composition of the membrane. With DPPC membranes, an affect is detected at temperatures lower than Tm. It corresponds to a decrease of the lipid ordering. With DPPC-cer membranes, the protein increases the acyl-chain packing order regardless of the temperature of the experiments (10 degrees C less than T less than 75 degrees C). No perturbation of Tm is observed after addition of ricin to either DPPC or DPPC-cer membranes. The different perturbations detected by Raman and FTIR suggest that ricin mainly interacts with the interfacial domains of the membranes.

A fluorometric study of the interaction of bradykinin with lipids

The interaction of bradykinin (BK) with lipids has been followed by steady-state fluorescence measurements. Addition of either cerebroside sulfate (CS) or phosphatidylinositol (PI), solubilized with the nonionic surfactant C12E8, to BK or its analogue [Gly6]-BK enhances the relative fluorescence intensity of peptide emission at 288 nm. Fluorometric titration of the peptide with lipid has been used to quantitate the interactions in terms of stoichiometry and equilibrium constant. Job's method of continuous variation for the BK-CS interaction gave a stoichiometry of 1:2 for the complex. The value of the equilibrium constant, K, for the interaction of either BK or [Gly6]-BK with CS is 1.5.10(4) M-1. The BK-PI interaction is weaker; K = 5.0.10(3) M-1. Although electrostatic forces no doubt play a major role in these interactions, measurements on the model peptide Gly-Phe-Gly indicate that the phenylalanine residues of BK are disposed in the hydrophobic environment provided by the lipid-C12E8 mixed micelle. 13C-NMR measurements on [99% 13C alpha-Gly6]-BK show that there is no change in its cis/trans ratio upon interaction with CS. The increase in the relative fluorescence intensity of BK accompanying its cooperative interaction with sodium dodecyl sulfate (SDS) implicates the role of hydrophobic forces in this interaction as well. These results bear on the interpretation of the changes in circular dichroism (CD) of BK caused by SDS.

Serum lipids and demyelination in experimental allergic encephalomyelitis induced by the increased encephalitogenicity of myelin basic protein given with galactocerebrospide

Cholesterol esters and free cholesterol were determined in the serum of guinea pigs with experimental allergic encephalomyelitis (EAE). EAE was induced by immunization with myelin basic protein (MBP) and galactocerebroside (GC). The results showed an increased content of cholesterol arachidonate and cholesterol linoleate during the period of clinical signs of EAE in comparison with the content of cholesterol esters in EAE induced by MBP without galactocerebroside. The content of free cholesterol was significantly reduced. Histological analyses showed intensive inflammatory lesions and demyelination which were not found in EAE induced by MBP without galactocerebroside.

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.

Thermotropic behavior of mixtures of glycosphingolipids and phosphatidylcholine: effect of monovalent cations on sulfatide and galactosylceramide

The thermotropic behavior of both sulfatide (3-sulfogalactosylceramide) and galactosylceramide in dielaidoylphosphatidylcholine (DEPC) liposomes was studied, using steady-state fluorescence polarization of parinaric acid isomers. The glycosphingolipid (GSL) concentration of the liposomes was varied from 0 to 100%, and phase diagrams were constructed. The data indicate that sulfatide and DEPC are immiscible in the gel phase at sulfatide mole ratios of less than 0.30. The temperature of onset of the gel-liquid-crystalline phase transition is higher in K+ -containing buffer than in osmotically equal Na+ -containing buffer. Similar measurements, using galactosylceramide, a neutral GSL, indicated that this lipid and DEPC are immiscible in the gel phase at galactosylceramide mole ratios of less than 0.40. In contrast to the results obtained with sulfatide, onset temperatures are identical in Na+- or K+-containing buffers. The phase properties of sulfatide/DEPC mixtures are shown to depend on the cation only when the sulfatides contain hydroxy fatty acids. Our observations indicate that physiologically relevant concentrations of monovalent cations affect motion and distribution of sulfatide in biological membranes and further implicate this GSL as an important determinant of function of the Na+,K+-ATPase. A preliminary report of these data [Rintoul, D.A., Welti, R., & Song, W. (1988) Biophys. J. 53, 126a].

Isolation and characterization of the alpha-galactosyl-1,4-beta-galactosyl-specific adhesin (P adhesin) from fimbriated Escherichia coli

The alpha-galactosyl-1,4-beta-galactosyl-specific adhesin (P adhesin) was isolated from the fimbria-adhesin complex (FAC) of recombinant Escherichia coli strains expressing the F7(1), F8, or F13 fimbrial antigens. Separation into fimbriae and adhesin was achieved by heating the FAC to 80 degrees C in the presence of Zwittergent 3-16. After removal of the fimbriae by precipitation with lithium chloride, the adhesin was purified by anion-exchange fast protein liquid chromatography in the presence of 4 M urea. The purified adhesins from the three strains had pIs of 4.8 to 5.0 and molecular weights of approximately 35,000. The fimbrillins were smaller, their molecular weights being different with different F antigens. The amino-terminal amino acid sequence of the F7(1)- and F13-derived adhesins were different, that of the F13-derived adhesin being identical to that extrapolated from the DNA sequence of the papG gene (B. Lund, G. Lindberg, B.-I. Marklund, and S. Normark, Proc. Natl. Acad. Sci. USA 84:5898-5902). An antiadhesive monoclonal antibody which reacted with the three P adhesins was prepared. The FAC and the purified adhesins but not the fimbriae from which the adhesins had been removed agglutinated erythrocytes and galactose-galactose-coated latex beads. The adhesion of erythrocytes to the surface-fixed adhesins could be specifically inhibited with alpha-galactosyl-1,4-beta-galactosyl-1,4-glucosyl. The results indicate that the P adhesin(s) of uropathogenic E. coli represents a group of related proteins with conserved receptor recognition domains. The F13-derived P adhesin is the PapG protein postulated by Normark and his colleagues (Lund et al., Proc. Natl. Acad. Sci. USA 84:5898-5902; B. Lund, F. Lindberg, and S. Normark, J. Bacteriol. 170:1887-1894).

Differential scanning calorimetric and Fourier transform infrared spectroscopic investigations of cerebroside polymorphism

Calorimetric and Fourier transform infrared (FTIR) spectroscopic studies have been made of the polymorphism exhibited by bovine brain cerebroside-water systems, and the effect of cholesterol and dipalmitoylphosphatidylcholine (DPPC) upon this polymorphism was investigated. The conversion of the cerebroside from the thermodynamically stable to the metastable form is found to be accompanied by spectral changes, indicating a decrease in cerebroside headgroup hydration and a rearrangement of the hydrogen-bond network. The incorporation of low concentrations of cholesterol and DPPC into cerebroside bilayers broadens the thermal transitions associated with the cerebroside as a result of the disruption of cerebroside-cerebroside interactions. This disruption is evident in the spectra of cerebroside/cholesterol mixtures.

Anisotropic 2H-nuclear magnetic resonance spin-lattice relaxation in cerebroside- and phospholipid-cholesterol bilayer membranes

The axially symmetric powder pattern 2H-nuclear magnetic resonance (NMR) lineshapes observed in the liquid crystalline phase of pure lipid or lipid/cholesterol bilayers are essentially invariant to temperature, or, equivalently, to variations in the correlation times characterizing C-2H bond reorientations. In either of these melted phases, where correlation times for C-2H bond motions are shorter than 10(-7) s, information on the molecular dynamics of the saturated hydrocarbon chain would be difficult to obtain using lineshape analyses alone, and one must resort to other methods, such as the measurement of 2H spin-lattice relaxation rates, in order to obtain dynamic information. In pure lipid bilayers, the full power of the spin-lattice relaxation technique has yet to be realized, since an important piece of information, namely the orientation dependence of the 2H spin-lattice relaxation rates is usually lost due to orientational averaging of T1 by rapid lateral diffusion. Under more favorable circumstances, such as those encountered in the lipid/cholesterol mixtures of this study, the effects of orientational averaging by lateral diffusion are nullified, due to either a marked reduction (by at least an order of magnitude) in the diffusion rate, or a marked increase in the radii of curvature of the liposomes. In either case, the angular dependence of 2H spin-lattice relaxation is accessible to experimental study, and can be used to test models of molecular dynamics in these systems. Simulations of the partially recovered lineshapes indicate that the observed T1 anisotropies are consistent with large amplitude molecular reorientation of the C-2H bond among a finite number of sites. Furthermore, from the observed orientation dependence of the 2H spin-lattice relaxation rates, we conclude that order director fluctuations cannot provide the dominant relaxation pathway for acyl chain deuterons.

Phase behavior of cerebroside and its fractions with phosphatidylcholines: calorimetric studies

Bovine brain cerebroside and its kerasin (beta-D-galactosyl-N-acyl-D-sphingosine) and phrenosin (beta-D-galactosyl-N-(2-D-hydroxyacyl)-D-sphingosine) fractions were mixed with diacylphosphatidylcholines (PCs) to form fully hydrated lamellar phases. These mixtures were examined by differential scanning calorimetry, and phase diagrams for cerebroside/diacylPC mixtures were constructed from the data. Cerebroside was found to be miscible with egg PC at low mole fractions X of cerebroside; the mixture behaves non-ideally for X greater than 0.25. The non-ideal behavior appears to be a superposition of separate interactions of kerasin and phrenosin with egg PC. Strikingly, phrenosin mixes nearly ideally with egg PC. Kerasin mixed with egg PC yields a peritectic phase diagram. Cerebroside and phrenosin were found to be immiscible with dimyristoylphosphatidylcholine (DMPC) in the gel state in low proportions. Both stable and metastable gel phases of kerasin were detected in different endotherms of kerasin/PC mixtures. Kerasin in the stable and metastable gel states exhibits discontinuous and continuous ranges of miscibility, respectively, with DMPC. The stable gel phase of kerasin does not segregate in natural cerebroside. Natural kerasin was found to act isomorphic to semi-synthetic (natural configuration) D-kerasins but not completely to synthetic DL-kerasins of single acyl chain lengths.