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PubMed2005

Nontypeable Haemophilus influenzae-binding gangliosides of human respiratory (HEp-2) cells have a requisite lacto/neolacto core structure.

Nontypeable Haemophilus influenzae (NTHI) are a major cause of human infections. We previously demonstrated high affinity and high specificity binding of NTHI to minor gangliosides of human respiratory (HEp-2) cells and macrophages, but not to brain gangliosides. We further identified the NTHI-binding ganglioside of human macrophages as alpha2,3-sialylosylparagloboside (IV3NeuAc-nLcOse4Cer, nLM1), which possesses a neolacto core structure that is absent in brain gangliosides. This supported a hypothesis that lacto/neolacto core carbohydrates are critical for NTHI-ganglioside binding. To investigate, we determined the core carbohydrate structure of NTHI-binding gangliosides of HEp-2 cells, through multiple approaches, including specific enzymatic degradation, mass spectral analysis and gas-liquid chromatography. Our analyses denote the following critical structural attributes of NTHI-binding gangliosides: (1) a conserved lacto/neolacto core structure; (2) requisite sialylation, which may be either internal or external, with alpha2,3 (human macrophages) or alpha2,6 (HEp-2 cells) anomeric linkages; (3) internalized galactose residues. Mass spectral and gas chromatographic analyses confirm that NTHI-binding gangliosides of HEp-2 cells possess lacto/neolacto carbohydrate cores and identify the structure of the major peak as NeuAcalpha2-6Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glcbeta1-1Cer (alpha2,6-sialosylparagloboside, nLM1). Collectively, our studies denote NTHI-binding gangliosides as lacto/neolacto series structures.

Bacterial Adhesion↗

PubMed1993

Aberrant expression of gangliosides in human renal cell carcinomas.

Aberrant and elevated ganglioside expression has been observed in neoplasms, and has been shown to be an important marker of tumor progression. We therefore studied the gangliosides of renal cell carcinoma (RCC) by analyzing gangliosides from 18 RCC biopsies, 10 RCC lines and 5 normal kidney biopsies. A comparison of tumor with normal tissue revealed a significant difference in individual ganglioside expression in which the former consistently expressed eight major gangliosides, GM3, GM2, GM1, GD3, GD1A, GD2, GD1B and GT1B, according to the nomenclature of Svennerholm. There was a notable significant mean increase in the expression of GM2, GM1 and GD1A and a significant decrease in the expression of GD3 in tumor tissue compared with normal kidney tissue. Compared with tumor biopsy tissue, RCC cell lines showed a significant decrease in the expression of GM3, but a significant increase in GM2, GM1 and GD2. There was a marked increase in a pathway gangliosides (GM2, GM1, and GD1a) in RCC biopsies and cell lines compared with normal kidney. These studies indicating that RCC have markedly aberrant ganglioside expression similar to neural origin tumors may relate to the activation of a ganglioside pathway enzymes. Gangliosides expressed on RCC tumors may be important markers of tumor progression and target antigens for immunotherapy.

Biomarkers, Tumor↗

PubMed1999

A specific loss of C-series gangliosides in pancreas of streptozotocin-induced diabetic rats.

Gangliosides in pancreas, kidney, and liver tissues from streptozotocin-induced diabetic rats were analyzed by methods including thin-layer chromatographic (TLC) immunostaining with a specific monoclonal antibody to c-series gangliosides. In rats suffering diabetes for one month, the composition of major gangliosides in pancreatic tissue was almost identical to control, except for a slight increase in the content of GM3. Though c-series gangliosides such as GT3, GT2, GQ1c, and CP1c were expressed in normal pancreatic tissue, they were practically lost in pancreas of diabetic animals. A specific loss of c-series gangliosides was also observed in pancreatic tissue from rats suffering diabetes only for three days. While the composition of major gangliosides in the kidney did not change, streptozotocin-induced diabetic conditions brought about significant increases in contents of practically all major ganglioside species in liver tissue. No change was observed in the amount and composition of c-series gangliosides in both tissues. These results strongly suggest that c-series gangliosides are specifically localized in pancreatic B cells.

Animals↗

PubMed2000

Inhibition of human platelet aggregation by gangliosides.

The content and composition of gangliosides is modified upon platelet stimulation, suggesting that these lipids may play functional roles in platelet physiology. Therefore, the effect of exogenously added gangliosides on human platelet aggregation was evaluated. The pretreatment of platelets with a mixture of total gangliosides from bovine brain and a series of purified mono-, di- and tri-sialogangliosides partially inhibit the collagen-induced aggregation process and ATP release and completely block the generation of the second aggregation wave when ADP is used as agonist. The inhibition was exerted at around 100 microM by G(TOT) as well as purified G(M1), G(M3), G(D1a), and G(T1b) gangliosides, whereas asialoG(M1) and sulphatide did not show a significant influence on platelet aggregation. Thrombin, Ca(2+) ionophores (A23187 and Ionomycin), arachidonic acid, and U46619 were unable to bypass the inhibitory effect exerted by gangliosides, suggesting that gangliosides inhibit platelet aggregation by inhibiting the synthesis or action of prostaglandins. Gangliosides inhibited U46619-induced aggregation, thus suggesting that they block the action of thromboxane A(2). Epinephrine induces a partial aggregation on gangliosides-treated platelets, similar to fluoroaluminate and phorbol myristate acetate, indicating that these platelets are still functional. To summarize, these results indicate that the major pathway(s), but not all, driving to the aggregation process following the interaction of ligand-receptor may be blocked by pretreatment of human platelets with gangliosides.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed1999

Occurrence of monosialosyl pentahexaosylceramide GalNAc-GM1 as specific tumor-associated ganglioside of human head and neck squamous cell carcinomas.

In a recent study of the ganglioside profiles of human head and neck squamous cell carcinomas versus normal tissue, one unidentified GX ganglioside was found exclusively in tumor extracts, migrating between GM1 and GD3 by thin-layer chromatography. To determine the chemical structure of this ganglioside which accounted for 3-8% of the total gangliosides, the lipid samples were pooled and separated by high-pressure liquid chromatography to obtain individual ganglioside species purified to homogeneity. The tumor-associated GX ganglioside was analyzed by gas-liquid chromatography, mass spectrometry and immunostaining on thin-layer plates with mouse monoclonal antibodies after enzymatic cleavage. The data allowed the identification of GX ganglioside as GalNAc-GM1 that has been reported as a very minor brain ganglioside in humans. Thus, GalNAc-GM1 is a specific tumor-associated ganglioside in human head and neck squamous cell carcinomas that could be potentially valuable for clinicians.

Carcinoma, Squamous Cell↗

PubMed1998

Gangliosides and glycosphingolipids of peripheral nervous system myelins--a minireview.

A summary is provided of the available data on the composition of gangliosides and glycosphingolipids in the peripheral nervous system (PNS) including myelins and their antigenic properties. The composition of gangliosides and glycosphingolipids in the PNS is very different from that in the central nervous system (CNS), both quantitatively and qualitatively. One major difference is the abundance of neolacto-series gangliosides in the PNS, with the backbone structure Gal beta 1-4GlcNAc beta1-3Gal beta 1-4Glc1-1'Cer. Their abundance contrasts with the abundance of ganglio-series gangliosides in the CNS. The neolacto-series gangliosides are localized mainly in the myelins of the PNS. In addition to gangliosides, other acidic and neutral glycosphingolipids in the neolactoseries are also characteristic of the myelins of the PNS. The ceramide (fatty acid and sphingosine base) compositions of gangliosides in the PNS are different from those in the CNS gangliosides, having greater percentages of long-chain fatty acids and dehydrosphingosines than found in the CNS gangliosides.

Animals↗

PubMed2004

Alterations in neuroblastoma ganglioside synthesis by induction of GD1b synthase by retinoic acid.

Recent findings link increased expression of the structurally complex 'b' pathway gangliosides GD1b, GT1b, GQ1b (CbG) to a favourable clinical and biological behaviour in human neuroblastoma (NB). Seeking a model to probe these observations, we evaluated four human NB cell lines. Very low CbG content (4-10%) in three of the four cell lines (LAN-5, LAN-1, SMS-KCNR) reflected the ganglioside pattern observed in the most aggressive NB tumours. Pharmacological alterations of complex ganglioside synthesis in vitro by a 5-7 day exposure to 5-10 microM retinoic acid, which is employed in maintenance therapy of disseminated NB, included markedly increased (i) relative expression of CbG (6.6+/-2.0-fold increase, P=0.037), (ii) relative expression of the analogous 'a' pathway gangliosides, termed CaG (6.4+/-1.4-fold increase in GM1a and GD1a; P=0.010), and (iii) total cellular ganglioside content (2.0-6.3-fold), which in turn amplified the accumulation of structurally complex gangliosides. Substantial increases (2.7-2.9-fold) in the activity of GD1b/GM1a synthase (beta-1,3-galactosyltransferase), which initiates the synthesis of CbG and CaG, accompanied the all-trans retinoic acid (ATRA)-induced ganglioside changes. Thus, increased CbG synthesis in NB cell lines is attributable to a specific effect of ATRA, namely induction of GD1b/GM1a synthase activity. Since the shift towards higher expression of CbG and CaG during retinoic acid-induced cellular differentiation reflects a ganglioside pattern found in clinically less-aggressive tumours, our studies suggest that complex gangliosides may play a role in the biological and clinical behaviour of NB.

Antineoplastic Agents↗

PubMed1983

Differences in liver ganglioside patterns in various inbred strains of mice.

The ganglioside patterns in the liver of different inbred and hybrid strains of mice were investigated. The inbred strains were Balb/cAnNCr1BR, C57BL/6NCr1BR, DBA/2NCr1BR. C3H/HeNCr1BR; the hybrid strain was the Swiss albino. The following major gangliosides were found to be present in mouse liver: GM3-NeuAc; GM3-NeuGl, GM2 [a mixture of one species carrying N-acetylneuraminic acid (NeuAc) and one carrying N-glycollylneuraminic acid (NeuGl)], GM1 and GD1a-(NeuAc,NeuGl). The qualitative and quantitative patterns of liver gangliosides were markedly different in the various inbred strains of mice; in Balb/cAnNCr1BR strain, ganglioside GM2 was preponderant (99.2% of total ganglioside content); in C57BL/6NCr1BR, the major ganglioside was GM2 (90.4%), followed by GM3-NeuAc (5.6%) and GM3-NeuGl (4.0%); in DBA/2NCr1BR, GM2 accounted for 77.1%, GD1a-(NeuAc,NeuGl) 18.9% and GM1 3.1% of gangliosides; in C3H/HeNCr1BR, GM2 constituted 50.6%, GM1 22.8% and GD1a-(NeuAc,NeuGl) 22.1%. In the hybrid Swiss albino mice, liver ganglioside composition markedly varied from one animal to another, GM3-NeuGl, GM2 and GD1a-(NeuAc,NeuGl) being the predominant gangliosides in the various cases.

Animals↗

PubMed1990

Subcellular biosynthesis and transport of gangliosides formed from exogenous lactosylceramide in rat liver.

In order to clarify the mechanisms of ganglioside biosynthesis and transport we intravenously administered a liposomal dispersion of radiolabelled lactosylceramide (LacCer) to rats and then followed the time course of the individual gangliosides which became radioactive in the Golgi-apparatus and plasma-membrane fractions prepared from the liver. After administration of radiolabelled LacCer the liver retained a substantial amount of radioactivity, which was distributed among an organic phase (mainly residual LacCer), a fraction containing low-Mr substances (mainly 3H2O) and a ganglioside fraction. The hepatocytes were found to provide the bulk of gangliosides biosynthesized from exogenous LacCer. After subcellular fractionation, the total radioactive gangliosides increased in the Golgi apparatus up to 8 h, to then decrease and practically disappear at 24 h; in the plasma membranes they were progressively concentrated, accounting for high absolute values. Ganglioside patterns were greatly modified with time in both the Golgi apparatus and plasma membrane, but without significant differences between them. Biosynthesis in the Golgi apparatus and accumulation in the plasma membrane of each individual ganglioside followed a precursor-product relationship. The obtained results indicated that once a ganglioside is biosynthesized in the Golgi apparatus, it is in part made available for translocation to the plasma membrane, which rapidly occurs, and is in part retained in the Golgi apparatus, where it acts as a precursor for the biosynthesis of more glycosylated gangliosides.

Animals↗

PubMed1998

Synthesis, shedding, and intercellular transfer of human medulloblastoma gangliosides: abrogation by a new inhibitor of glucosylceramide synthase.

The biological activity of human medulloblastoma tumor gangliosides very likely involves the interaction of these molecules with host cells in the tumor microenvironment. To trace the hypothesized intercellular transfer of shed medulloblastoma gangliosides, we used an in vitro dual-chamber culture system in which the tumor cells, the shed gangliosides, and the target cells to which they might bind would not be perturbed during the transfer process. We observed that under these unmanipulated conditions, gangliosides were shed by the Daoy medulloblastoma cell line (approximately 300 pmol/10[8] cells/h), traversed the chamber membrane, and stably bound to the target fibroblasts at the very high density of 10(7) molecules per cell within 48 h. To determine if this substantial intercellular transfer of shed gangliosides, with its potential of modifying target cell function, could be blocked, we evaluated a new inhibitor of glucosylceramide synthase, DL-threo-1-phenyl-2-hexadecanoylamino-3-pyrrolidino-1-propanol (PPPP). PPPP (1.0 microM) reduced (90%) Daoy cell ganglioside content strikingly, without causing toxicity or inhibiting cell proliferation. Subsequently, ganglioside shedding by the medulloblastoma cells was diminished significantly (to approximately 50 pmol/10[8]/h), and binding of radiolabeled shed medulloblastoma gangliosides to target fibroblasts was consequently almost completely abrogated. We conclude that the shedding and transfer of potentially biologically active human medulloblastoma gangliosides can be diminished effectively by PPPP.

Binding Sites↗

PubMed1986

Fibrillar organization of fibronectin is expressed coordinately with cell surface gangliosides in a variant murine fibroblast.

NCTC 2071A cells, a line of transformed murine fibroblasts, grow in serum-free medium, are deficient in gangliosides, synthesize fibronectin, but do not retain and organize it on the cell surface. When the cells are exposed to exogenous gangliosides, fibrillar strands of fibronectin become attached to the cell surface. A morphologically distinct variant of NCTC 2071A cells was observed to both retain cell surface fibronectin and organize it into a fibrillar network when the cells were stained with anti-fibronectin antibodies and a fluorescent second antibody. A revertant cell type appeared to resemble the parental NCTC 2071A cells in terms of morphology and fibronectin organization. All three cell types were subjected to mild NaIO4 oxidation and reduction with KB3H4 of very high specific radioactivity in order to label the sialic acid residues of surface gangliosides. The variant had much more surface gangliosides than the parental, particularly more complex gangliosides corresponding to GM1 and GD1a. The surface gangliosides of the revertant were intermediate between the parental and the variant. By using sialidase, which hydrolyzes GD1a to GM1, and 125I-labeled cholera toxin, which binds specifically to GM1, the identity and levels of these gangliosides were confirmed in the three cell types. When variant cells were exposed to sialidase for 2 d, there appeared to be little change in fibronectin organization. Concomitant treatment of the cells with the B subunit of cholera toxin, which bound to all the surface GM1 including that generated by the sialidase, however, eliminated the fibrillar network of fibronectin. In addition, exposure of the variant cells to a 70,000-mol-wt fragment of fibronectin, which lacks the cell attachment domain but contains a matrix assembly domain, inhibited the formation of fibers. Finally, all three cell types were assayed for their ability to attach to and spread on fibronectin-coated surfaces; no significant differences were found. Our results further establish that the ability of a cell to organize fibronectin into an extracellular matrix is dependent on certain gangliosides, but they also indicate that cell adhesion to fibronectin is independent of these gangliosides. We suggest that matrix organization and cell attachment and spreading are based on separate mechanisms and that these functions are associated with different cell surface "receptors."

Animals↗

PubMed1984

Receptors for human alpha interferon: are gangliosides involved?

Interferon (IFN) action on cells must begin with an interaction with cellular receptors. Binding and cross-linking experiments reported earlier with purified 125I-labeled recombinant human (Hu) IFN-alpha 2 have revealed that IFN-alpha 2 binds to a specific macromolecular receptor on human cells (Joshi et al., J. Biol. Chem. 257, 13884-13887, 1982). Based on indirect evidence such as neutralization of the antiviral action of IFN preparations by gangliosides and binding of IFNs to gangliosides coupled to solid supports, it has been suggested by various investigators that gangliosides may be a part of the IFN-alpha/beta receptors. Experiments presented here indicate that gangliosides could block the antiviral activity of HuIFN-beta, but not of HuIFN-alpha, although both species of IFN bound strongly to gangliosides coupled to poly-L-lysine-agarose. Furthermore, gangliosides did not inhibit the binding of 125I-labeled HuIFN-alpha 2 to specific receptors on human cells, and this binding was competed out by unlabeled HuIFN-alpha 2 and HuIFN-alpha(LE) which were preincubated with gangliosides. However, the capacity of HuIFN-beta to compete for the receptors was abolished by preincubation with gangliosides. These results were confirmed by cross-linking experiments to identify the IFN-receptor complex by gel electrophoresis. The results indicate that at least in the case of HuIFN-alpha species, the ganglioside binding is apparently not at the active site of the IFN molecules required for interaction with the receptors on the cell surface.

Binding Sites↗

PubMed1993

The 3G11+ antigen, a marker for murine CD4+ TH1 lymphocytes, is a ganglioside.

Two monoclonal antibodies (mAbs), SM3G11 and SM6C10, can be used to discriminate between functionally distinct murine CD4+ T cell subsets. In this study we use high-performance thin-layer chromatography and immunostaining techniques to show that the 3G11 mAb reacts with two bands of a ganglioside fraction from murine spleen and thymus, and rat spleen. The 6C10 antibody shows no evidence of glycolipid reactivity. The 3G11+ bands have a mobility between those of the reference gangliosides GD1a and GD1b from human brain. The 3G11+ reactive bands were eluted in the disialyl fraction of rat spleen gangliosides using DEAE anion-exchange chromatography. Treatment of spleen gangliosides with endoglycoceramidase eliminates 3G11 antibody binding over time, indicating that the antigen contains a Glc beta 1-1'ceramide linkage, characteristic of a glycosphingolipid. Treatment of thymus or spleen gangliosides with sialidase eliminates binding of 3G11, thus indicating that the 3G11 epitope is dependent on the expression of one or more sialic acid residues. Immunostaining studies with a variety of reagents indicate that the 3G11+ gangliosides: (i) probably do not contain either the asialo-GM1 or the GM1 core structures; (ii) are not recognized by mAbs specific for the oligosaccharides of asialo-GM2, GM2, GD2 and GD3 gangliosides; and (iii) are also not recognized by antibodies or reagents that are specific for several structures representative of other major glycosphingolipid classes. Overall, these studies strongly suggest that the 3G11+ gangliosides have structures that have not been previously recognized in murine lymphoid tissue. Structures that could account for the known properties of the 3G11+ molecules are described. Finally, ways in which the selective expression of 3G11+ gangliosides might be linked to functionally distinct T-cell behaviours are discussed.

Animals↗

PubMed1997

Application of matrix-assisted laser desorption ionization time-of-flight mass spectrometry with delayed ion extraction to ganglioside analyses.

Various monosialo- and disialo-gangliosides and their derivatives were examined by delayed ion extraction matrix-assisted laser desorption ionization time-of-flight mass spectrometry (DE MALDI-TOF MS) in the reflector mode with alpha-cyano-4-hydroxycinnamic acid or 2,5-dihydroxybenzoic acid used as the matrix. Native gangliosides were generally found to give good spectra in the negative ion mode. 2,5-Dihydroxybenzoic acid was a better matrix for gangliosides than alpha-cyano-4-hydroxycinnamic acid, because this matrix seemed to minimize loss of sialic acid and carbon dioxide of gangliosides. About 1 pmol of ganglioside was able to be detected with this matrix. When "A-series" gangliosides such as GD1a and GalNAc-GD1a gave undesirable extra peaks probably due to loss of sialic acid besides molecule-related ion peaks, the methyl-esterification of the gangliosides at the carboxyl groups of sialic acids was found to be necessary to obtain good DE MALDI-TOF mass spectra in the positive ion mode. In contrast, "B-series" gangliosides such as GD1b, GD2, and GD3 gave rise to major dehydrated molecule-related ion [M-H2O-H]- peaks in the negative ion mode without the pretreatment of methyl-esterification. The DE MALDI-TOF mass spectrometric analysis enabled us to distinguish between GD1a and GD1b, which have the same molecular weight. It was also found that not only a purified sample, but also a mixed sample of various gangliosides was amenable to the identification of them by DE MALDI-TOF MS.

Carbohydrate Conformation↗

PubMed1998

Nerve growth factor-induced neurite formation in PC12 cells is independent of endogenous cellular gangliosides.

The PC12 rat pheochromocytoma cell line is an established model for nerve growth factor (NGF)-induced neurite formation. It has been shown that when gangliosides are added to the culture medium of PC12 cells, NGF-induced neurite formation of PC12 cells is enhanced. To determine the role of endogenous cellular gangliosides themselves in NGF-elicited neurite formation, we depleted cellular gangliosides using the new specific glucosylceramide synthase inhibitor, d, l-threo-1-phenyl-2-hexadecanoylamino-3-pyrrolidino-1-propanol.HCl (PPPP). 0.5-2 microM PPPP rapidly inhibited ganglioside synthesis and depletedcellular gangliosides. Nonetheless, over a concentration range of 5-100 ng/ml NGF, in both low serum and serum-free medium, neurite formation was normal. Even pretreatment of PC12 cells for up to 6 days with 1 microM PPPP followed by cotreatment with PPPP and NGF for 10 days, still did not inhibit neurite formation. The conclusion that ganglioside depletion did not block neurite formation stimulated by NGF was supported by the lack of effect of PPPP, under these same conditions, on cellular acetylcholine esterase activity, a neuronal differentiation marker (73.8 +/- 12.1 versus 67.2 +/- 4.6 nmol/min/mg protein at 50 ng/ml NGF; control versus 1 microM PPPP). These findings, together with previous studies showing enhancement of NGF-induced neurite formation by exogenous gangliosides, underscore the vastly different effects that exogenous gangliosides and endogenous gangliosides may have upon cellular functions.

Acetylcholinesterase↗

PubMed2005

Dietary ganglioside decreases cholesterol content, caveolin expression and inflammatory mediators in rat intestinal microdomains.

Membrane microdomains rich in cholesterol and sphingolipids, including gangliosides (GGs), are known to be important regions for cell signaling and binding sites for various pathogens. Cholesterol depletion inhibits the cellular entry of pathogens and also reduces inflammatory signals by disrupting microdomain structure. Our previous study showed that dietary gangliosides increased total ganglioside incorporation while decreasing cholesterol in the intestinal mucosa. We hypothesized that diet-induced reduction in cholesterol content in the intestinal mucosa disrupts microdomain structure resulting in reduced pro-inflammatory signals. Male weanling Sprague-Dawley rats were fed semipurified diets for 2 weeks. Experimental diets were formulated to include either ganglioside-enriched lipid (GG diet, 0.02% gangliosides [w/w of diet] ) or polyunsaturated fatty acid (PUFA diet, 1% arachidonic acid and 0.5% docosahexaenoic acid, w/w of total fat), in a control diet containing 20% fat. Levels of cholesterol, GG, caveolin, platelet activating factor (PAF), and diglyceride (DG) were measured in the microdomain isolated from the intestinal brush border. The GG diet increased total gangliosides by 50% with a relative increase in GD3 and a relative decrease in GM3. Cholesterol content was also reduced by 23% in the intestinal microdomain. These changes resulted in a significant decrease in the ratio of cholesterol to ganglioside. The GG diet and the PUFA diet were both associated with reduction in caveolin, PAF, and DG content in microdomains, whereas no change occurred in the ganglioside profile of animals fed the PUFA diet. Dietary gangliosides decrease the cholesterol/ganglioside ratio, caveolin, PAF and DG content in microdomains thus exerting a potential anti-inflammatory effect during gut development.

Animals↗

PubMed1996

Interaction of ganglioside with specific peptide sequences as a mechanism for the modulation of calmodulin-dependent enzymes.

We examined the interaction between gangliosides and synthetic peptides of calmodulin (CaM)-dependent enzymes to confirm the hypothesis that interaction between gangliosides and the CaM-like site (CLS) of the enzyme is a mechanism for the modulation of the enzyme activity by gangliosides. Gangliosides, GD1b, GT1b, and GD1a, inhibited the activity of CaM-independently activated cAMP-phosphodiesterase and their inhibition was cancelled by a peptide consisting of 17 amino acid residues of a plasma membrane Ca(2+)-pump CLS, suggesting the involvement of the interaction between the peptide and the gangliosides. The peptide of an assumed CLS of phosphodiesterase also cancelled the inhibition. On the other hand, the gangliosides interacted with synthetic CaM-binding site (CBS) peptides of phosphodiesterase, calcineurin, Ca(2+)-pump, and Ca2+/calmodulin-dependent protein kinase II. Moreover, gangliosides GM3 and LM1, that activate but do not inhibit phosphodiesterase, interacted with the CBS peptides, whereas they did not bind to CLS peptides. On the basis of these new findings, we propose a revised model for the ganglioside-mediated modulation of CaM-dependent enzymes, i.e. without CaM, gangliosides bind to CBS and thus stimulate the enzyme activity, acting like CaM. At higher concentrations, they bind to CLS of the enzymes as well and inhibit the activity, acting like the CBS of the enzyme.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1988

Thermotropic behavior and electronmicroscopic structures of mixtures of gangliosides and dipalmitoylphosphatidylcholine.

The calorimetric properties and morphological structures of dispersed mixtures of 1, 2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and highly purified human brain gangliosides, GM2, GM1, GD1a, GD1b, and GT1b, were studied using a high-sensitivity differential scanning calorimeter and an electron-microscope, as a function of the ganglioside molar fraction. No thermal phase transitions of pure gangliosides in aqueous dispersions could be detected. In the mixtures of DPPC and gangliosides, the gel to liquid crystalline phase transition occurred at a higher temperature than in pure DPPC dispersions and progressed over a wide temperature range. As increasing amounts of the pure ganglioside species were added to DPPC, the temperature for the main transition gradually increased. The phase transition progressed differently among different gangliosides/DPPC mixtures. The enthalpy values were found to decrease linearly as the number of sialic acid residues increased. Electron-microscopically the ganglioside/DPPC mixtures formed multilamellar structures at lower concentrations of the gangliosides, and the structures changed to cylindrical and spherical micelles as the ganglioside concentration was increased. The polysialoganglioside/DPPC mixtures showed the micellar form even at lower ganglioside concentrations, contrary to the case of the monosialoganglioside/DPPC mixtures. The morphological changes of gangliosides/DPPC mixtures corresponded with changes in the calorimetric properties. These results show that individual gangliosides have different physicochemical effects on model membranes, possibly because of the interaction of their negatively charged head groups.

1,2-Dipalmitoylphosphatidylcholine↗