Interaction of low-density lipoproteins with gangliosides.

The ganglioside uptake capacity of human serum low-density lipoproteins (LDL), the mode of ganglioside-LDL binding, and the influence of gangliosides on the floatation properties, size distribution, stability and fluorescence of LDL were investigated. The data obtained suggest that both hydrophobic and electrostatic forces are involved in formation of ganglioside-LDL complexes, but the former appear to be more important. Although association of gangliosides with LDL is predominantly unspecific, nonsaturable, and weak, a small saturable component due to specific ganglioside-apolipoprotein binding, also appears to be involved. In the presence of gangliosides the lipoprotein particles aggregate, the intrinsic fluorescence of LDL and their interaction with antibodies against apo-B change indicating that the state of apo-B [corrected] is modified by gangliosides.

Interaction of influenza virus with gangliosides and liposomes containing gangliosides.

It has already been shown that influenza virus binds unspecifically to liposomes containing ganglioside GM1 wheras with gangliosides GD1b and GT1b binding occurs in a specific and saturable manner [Slepushkin et al. (1986) Biol. Membr. 3, 229-235]. In the present study the mode of interaction between influenza virus and various gangliosides or phospholipid liposomes containing cholesterol and gangliosides has been investigated. The influence of exogenous gangliosides on the structure of the viral envelope was studied using fluorescent and photoactivatable phospholipids incorporated into the viral membrane. With both types of probes maximal effects of gangliosides were caused by GT1b. Addition of that ganglioside resulted in a marked decrease in the fluorescence polarization (P) of fluorescent labeled virus as well as in substantial changes in the binding of photoactivatable analogues of sphingomyelin and phosphatidylcholine to virus proteins, mainly hemagglutinin. The effects of GT1b and GD1b on P value were comparable, whereas gangliosides with other oligosaccharide chains caused much smaller changes in P. Furthermore GT1b but not GM1 influenced phospholipid-hemagglutinin cross-linking. Interaction of the virus with large unilamellar liposomes was monitored by two fluorescence assays based on resonance-energy transfer from the tryptophans and tyrosines of viral proteins to vesicles labeled with a triacylglycerol (anthrylvinyldioleoylglycerol) or from these labeled vesicles to virions labeled with a perylenoyl derivative of galactosylcerebroside (PGalSph). A third fluorescence assay was based on relief of self-quenching in PGalSph-labeled virions, upon low-pH-induced virus-liposome fusion. With all three fusion assays the changes of fluorescence caused by GT1b were more pronounced than those induced by GM1. On the other hand, virus-induced release of [14C]glucose from multilamellar liposomes was enhanced by GM1 but not by GT1b or GD1b. It is concluded that the interaction of GT1b or GD1b with virus hemagglutinin induces a rearrangement of the viral lipids rendering lipid bilayer areas of the viral envelope significantly fluid, which in turn promotes fusion of the virus with target membranes. Probably virus-liposome fusion and virus-induced liposome leakage are brought about by different mechanisms depending on specific or unspecific binding of the virions to the target.

[Interaction of gangliosides with low-density proteins from human blood]. / Vzaimodeistvie gangliozidov s lipoproteinami nizkoi plotnosti krovi cheloveka.

Gangliosides have been shown to modulate the receptor-mediated endocytosis of low density lipoproteins (LDL). The direct interaction of LDL with various gangliosides has been studied. Binding of gangliosides to LDL immobilized on CNBr-Sepharose (LDL-Sepharose) and the influence of gangliosides on the fluorescence of LDL containing anthrylvinyl-labeled sphingomyelin were investigated. The binding of 3H-gangliosides to LDL-Sepharose, as well as fluorescence polarization of LDL were found to depend on the structure and concentration of the gangliosides in a specific saturable manner. The data obtained indicate that gangliosides interact with apolipoprotein B via specific binding sites.

[Gangliosides--specific receptors for the influenza virus]. / Gangliozidy--spetsificheskie retseptory dlia virusa grippa.

The capacity of two gangliosides, GD1a and GT1b isolated from bovine brain to function as specific receptors of influenza virus was determined. A primary chick fibroblast culture was treated with neuraminidase to destroy natural receptors, the cells were loaded with gangliosides GD1a and GT1b, inoculated with 3H-uridine-labeled virus, and virus adsorption and penetration into the cell nucleus were determined. Both gangliosides were shown to restore virus adsorption to the cell surface and penetration of viral structures into the cell, GT1b facilitating more effective transportation of viral structures into the nuclei than GD1a and inducing penetration into the nuclei nearly 1.5-fold as much amount of viral structures as in native cells. The same ganglioside partially restored virus-induced hemolysis upon loading it on erythrocytes pre-treated with neuraminidase. It is concluded that ganglioside GT1b is a specific receptor for influenza virus. 3.9% of this ganglioside was found in chick fibroblast lipids.

A sphingomyelin transfer protein in rat tumors and fetal liver.

The binding of the disaccharides methyl beta-D-lactoside and 2-acetamido-2-deoxy-3-O-(beta-D-galactopyranosyl)-beta-D-galactopyranose [beta-D-Gal-(l leads to 3)-D-GalNAc] to peanut agglutinin was studied by ultraviolet difference spectroscopy. The magnitude of the difference spectra varied with the concentration of the carbohydrates; association constants and thermodynamic parameters were determined from titration experiments at different temperatures. The enthalpy and entropy changes for binding of methyl beta-D-lactoside were found to be delta H degree = -65 +/- 4 kJ mol-1, delta S degree = -156 +/- 14 J mol-1 K-1. For beta-D-Gal-(1 leads to 3)-D-GalNAc the observed thermodynamic parameters were delta H degree = -78 +/- 5 kJ mol-1, delta S degree = -177 +/- 16 J mol-1 K-1. For both disaccharides, the enthalpy change upon binding to the lectin is much larger than found for the binding site on peanut agglutinin. The observed parameters are compared with those found for the binding of monosaccharides and oligosaccharides to other lectins and to lysozyme. Molecular models of the minimum energy conformers of beta-D-Gal(1 leads to 3)-D-GalNAc and methyl beta-D-lactoside are used to interpret the interaction of these, and structurally related ligands, with the peanut agglutinin binding site.

[Immunological detection of sphingomyelin exchange protein in tumors and in embryonic rat liver]. / Immunologicheskoe obnaruzhenie sfingomielinperenosiashchego belka v opukholiakh i embrional'noi pecheni krys.

The interaction of postmicrosomal supernatants from the Jensen sarcoma, sarcoma 45, nephroma RA, normal, regeherating and fetal rat livers with antisera to the sphingomyelin exchange protein isolated from hepatoma 27 was studied by double immunodiffusion. It was shown that this protein is present in comparable amounts in all the tumours tested and in fetal rat liver, whereas in normal and regenerating liver its content is negligible. Based on the correlation between the content of sphingomyelin exchange protein in cell cytosols and the amount of sphingomyelin in the corresponding mitochondria it is suggested that this protein is responsible for the presence of sphingomyelin in mitochondria.

[Phospholipid composition of mitochondria and microsomes from some transplantable rat tumors]. / Fosfolipidnyi sostav mitokhondrii i mikrosom nekotorykh perevivaemykh opukholei krys.

The phospholipid compositions of mitochondria and microsomes from rat liver, kidney, nephroma RA and sarcoma 45 were investigated. The "lipid dedifferentiation" of hepatoma membranes found earlier was shown to extend also to other tumours. However, this phenomenon may concern some, but not all phospholipids.

A universal lipid exchange protein from rat hepatoma.

The postmicrosomal protein fraction from rat hepatoma 27 adjusted to pH 5.1 stimulates phospholipid exchange between rat liver microsomes and mitochondria with higher rates and in a less specific way than the corresponding fraction from rat liver. A phospholipid exchange protein has been purified to homogeneity from the hepatoma pH-5.1 supernatant by gel filtration on Sephadex G-75 and ion-exchange chromatography on carboxymethylcellulose. The isolated protein had a molecular weight of 11200 as determined by electrophoresis on polyacrylamide in the presence of dodecyl sulfate and of 11168 as calculated from the amino acid composition. Isoelectric focusing showed a single band at pH 5.2. in the assay system rat liver microsomes leads to mitochondria the protein exhibits a complete lack of substrate specificity transferring all the major microsomal phospholipids to about the same extent. The possible role of the isolated phospholipid exchange protein in the chemical dedifferentiation of hepatoma cell membranes is discussed.

[Phospholipid exchange between mitochondria and microsomes of rat hepatoma 27]. / Obmen fosfolipidami mezhdu mitokhondriiami i mikrosomami gepatomy 27 krys

The phospholipid exchange in vitro between mitochondria and microsomes from rat liver and rat hepatoma 27 was investigated. On incubation with a postmicrosomal protein fraction the phospholipid exchange between subcellular fractions of the tumor was found to proceed much faster and less specific than between mitochondria and microsomes from normal liver. These results indicate that the earlier demonstrated lipid dedifferentiation of tumor cell membranes may be connected with an altered transmembrane phospholipid exchange in vivo.

[The relationship between cholesterol, shpingomyelin and phosphatidyl choline in liver and hepatoma cell membranes]. / Sootnosheniia kholesterina, sfingomielina i fosfatidilkholina v kletochnykh membranakh gepatomy i pecheni

The cholesterol, sphingomyelin and phosphatidylcholine content in different cell membranes of liver and hepatoma was studied. Significant amounts of cholesterol were found in all the subcellular fractions of hepatoma, whereas in the liver cholesterol is localized mainly in the plasma membranes. A direct relation between the content of cholesterol and sphingomyelin was demonstrated. Possible effects of the cholesterol : : sphingomyelin : phosphatidylcholine ratio on the properties of cell membranes are discussed.