Biosynthesis and functions of gangliosides: recent advances

Neural-specific alterations in glycosphingolipid biosynthesis and cell signaling associated with two human ganglioside GM3 synthase deficiency variants

GM3 Synthase Deficiency (GM3SD) is a neurodevelopmental disorder resulting from pathogenic variants in the ST3GAL5 gene, which encodes GM3 synthase, a glycosphingolipid (GSL)-specific sialyltransferase. This enzyme adds a sialic acid to the terminal galactose of lactosylceramide (LacCer) to produce the monosialylated ganglioside GM3. In turn, GM3 is extended by other glycosyltransferases to generate nearly all the complex gangliosides enriched in neural tissue. Pathogenic mechanisms underlying the neural phenotypes associated with GM3SD are unknown. To explore how loss of GM3 impacts neural-specific glycolipid glycosylation and cell signaling, GM3SD patient fibroblasts bearing one of two different ST3GAL5 variants were reprogrammed to induced pluripotent stem cells (iPSCs) and then differentiated to neural crest cells (NCCs). GM3 and GM3-derived gangliosides were undetectable in cells carrying either variant, while LacCer precursor levels were elevated compared to wildtype (WT). NCCs of both variants synthesized elevated levels of neutral lacto- and globo-series, as well as minor alternatively sialylated GSLs compared to WT. Ceramide profiles were also shifted in GM3SD variant cells. Altered GSL profiles in GM3SD cells were accompanied by dynamic changes in the cell surface proteome, protein O-GlcNAcylation, and receptor tyrosine kinase abundance. GM3SD cells also exhibited increased apoptosis and sensitivity to erlotinib-induced inhibition of epidermal growth factor receptor signaling. Pharmacologic inhibition of O-GlcNAcase rescued baseline and erlotinib-induced apoptosis. Collectively, these findings indicate aberrant cell signaling during differentiation of GM3SD iPSCs and also underscore the challenge of distinguishing between variant effect and genetic background effect on specific phenotypic consequences.

Bacterial toxins and heart function: heat-labile Escherichia coli enterotoxin B promotes changes in cardiac function with possible relevance for sudden cardiac death

Bacterial toxins can cause cardiomyopathy, though it is not its most common cause. Some bacterial toxins can form pores in the membrane of cardiomyocytes, while others can bind to membrane receptors. Enterotoxigenic E. coli can secrete enterotoxins, including heat-resistant (ST) or labile (LT) enterotoxins. LT is an AB5-type toxin that can bind to specific cell receptors and disrupt essential host functions, causing several common conditions, such as certain diarrhea. The pentameric B subunit of LT, without A subunit (LTB), binds specifically to certain plasma membrane ganglioside receptors, found in lipid rafts of cardiomyocytes. Isolated guinea pig hearts and cardiomyocytes were exposed to different concentrations of purified LTB. In isolated hearts, mechanical and electrical alternans and an increment of heart rate variability, with an IC50 of ~0.2 μg/ml LTB, were observed. In isolated cardiomyocytes, LTB promoted significant decreases in the amplitude and the duration of action potentials. Na+ currents were inhibited whereas L-type Ca2+ currents were augmented at their peak and their fast inactivation was promoted. Delayed rectifier K+ currents decreased. Measurements of basal Ca2+ or Ca2+ release events in cells exposed to LTB suggest that LTB impairs Ca2+ homeostasis. Impaired calcium homeostasis is linked to sudden cardiac death. The results are consistent with the recent view that the B subunit is not merely a carrier of the A subunit, having a role explaining sudden cardiac death in children (SIDS) infected with enterotoxigenic E. coli, explaining several epidemiological findings that establish a strong relationship between SIDS and ETEC E. coli.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12551-023-01100-6.

Chemical Synthesis of Gangliosides

Synthetic methodologies for gangliosides have evolved over the past three decades. The strategies for constructing ganglioside skeletons can generally be classified as late-stage ceramide coupling, the glucosyl ceramide cassette strategy, or late-stage sialylation. Using these synthetic strategies, numerous natural gangliosides and their structural analogs, including functional probes, have been synthesized. This chapter describes the synthetic strategies for gangliosides and provides examples of the total synthesis of several gangliosides using each strategy.

The Effect of GD1a Ganglioside-Expressing Bacterial Strains on Murine Norovirus Infectivity

In this study, we investigated the impact of GD1a-expressing bacterial strains on the infectivity of murine norovirus (MNV). Eligible bacterial strains were screened from a sewage sample using flow cytometry, and their genetic sequences of 16S rRNA were determined. The enzyme-linked immunosorbent assay (ELISA) was employed to analyze the binding between bacteria and MNV particles, and the plaque assay was used to assess the effects of GD1a-positive and negative strains on MNV infectivity. The result from ELISA shows that MNV particles are able to bind to both GD1a-positive and negative bacterial strains, but the binding to the GD1a-positive strain is more significant. The infectivity assay result further shows that the MNV infectious titer declined with an increasing concentration of GD1a-positive bacteria. The addition of anti-GD1a antibody in the infectivity assay led to the recovery of the MNV infectious titer, further confirming that the binding between MNV particles and bacterial GD1a ganglioside compromises MNV infectivity. Our findings highlight the role indigenous bacteria may play in the lifecycle of waterborne enteric viruses as well as the potential of exploiting them for virus transmission intervention and water safety improvement.

RNA Sequencing-Based Identification of Ganglioside GD2-Positive Cancer Phenotype

The tumor-associated ganglioside GD2 represents an attractive target for cancer immunotherapy. GD2-positive tumors are more responsive to such targeted therapy, and new methods are needed for the screening of GD2 molecular tumor phenotypes. In this work, we built a gene expression-based binary classifier predicting the GD2-positive tumor phenotypes. To this end, we compared RNA sequencing data from human tumor biopsy material from experimental samples and public databases as well as from GD2-positive and GD2-negative cancer cell lines, for expression levels of genes encoding enzymes involved in ganglioside biosynthesis. We identified a 2-gene expression signature combining ganglioside synthase genes ST8SIA1 and B4GALNT1 that serves as a more efficient predictor of GD2-positive phenotype (Matthews Correlation Coefficient (MCC) 0.32, 0.88, and 0.98 in three independent comparisons) compared to the individual ganglioside biosynthesis genes (MCC 0.02-0.32, 0.1-0.75, and 0.04-1 for the same independent comparisons). No individual gene showed a higher MCC score than the expression signature MCC score in two or more comparisons. Our diagnostic approach can hopefully be applied for pan-cancer prediction of GD2 phenotypes using gene expression data.

Counter effects of Asiaticosids-D through putative neurotransmission on rotenone induced cerebral ganglionic injury in Lumbricus terrestris

Asiaticoside-D (AD) was shown to efficacy of ganglionic degenerated Lumbricus terrestris as a pioneering observation in our earlier research. Though, extract molecular mechanisms of AD for degenerative diseases (DDs) remains largely unknown. We investigated the neuroprotective effects of AD against ROT in cerebral ganglions (CGs) of degenerative L. terrestris. Worms were exposed to 0.4 ppm ROT for 7 days were subjected to co- treatment with 15 ppm of AD. After, CGs was removed. The levels oxidant, non-antioxidant, antioxidant status, ganglioside, ceramide and ceramide glycanase (CGase) were estimated. The m-RNA levels of dopamine transporter (DAT), octopamine transporter (OAT), innexins-9 (inx-9), ionotropic glutamate receptor 3 (iGlu3), heat shock proteins (hsp70), XPRLamide neuropeptide precursor, tyramine beta-hydroxylase (tbh-1) and β- adrenergic receptor kinase-2 (β-ARK2-3) by semi-qRT- PCR. The expression pattern of tyramine beta hydroxylase (TBH), glutamate receptor (iGluR), serotonin transporter (SERT), dopamine transporters (DAT), nerve growth factors (NGF), cytochrome C oxidase (COC), NADH dehydogenase subunit-1 (ND-1), neurotrophin receptor p75 (p75NTR), neuronal nitric oxiside synthase (nNOs) interleukin 1- beta (IL1-β) and tumor necrosis factor alpha (TNF-α) by western blotting. Glutaminergic, serotogenic and dopaminergic toxicity variations were also performed. The levels of oxidant, non-antioxidant, antioxidant status, lipids, proteins and m-RNAs were significantly altered (p < 0.001) on ROT-induced (group II) and their levels were significantly changes (p < 0.05) by ROT+AD in CGs. The sensitive study plan concluded the neuroprotective effects of AD against ROT induced degeneration in worms and suggest that the AD deserves future studies for its use as an effective alternative medicine that could minimize the morbidity of ganglionic degenerative diseases patients.

On-chip biosynthesis of GM1 pentasaccharide-related complex glycans

A novel strategy for on-chip enzymatic glycosylation of complex glycans and direct analysis of glycan-related interactions is reported.

Chemical Synthesis of Gangliosides

Various methods for the chemical synthesis of gangliosides have been investigated to date and numerous natural gangliosides and their structural analogues have been synthesized during the past three decades. Key technologies in the synthesis of gangliosides include α-selective sialylation and introduction of the ceramide moiety into the oligosaccharide chain. This chapter introduces two major strategies for ganglioside synthesis-the most commonly used strategy and the recently developed glucosylceramide cassette approach. Synthetic procedures for selected reactions are also presented.

Disialyl GD2 ganglioside suppresses ICAM-1-mediated invasiveness in human breast cancer MDA-MB231 cells

The disialoganglioside GD3 has been considered to be involved in tumor progression or suppression in various tumor cells. However, the significance of the biological functions of GD3 in breast cancer cells is still controversial. This prompted us to study the possible relationship(s) between GD3 expression and the metastatic potential of a breast cancer MDA-MB231 cells as an estrogen receptor negative (ER-) type. The human GD3 synthase cDNA was transfected into MDA-MB231 cells, and G-418 bulk selection was used to select cells stably overexpressing the GD3 synthase. In vitro invasion potentials of the GD3 synthase over-expressing cells (pc3-GD3s) were significantly suppressed when compared with control cells. Expression of intercellular adhesion molecule-1 (ICAM-1; CD54) was down-regulated in the pc3-GD3s cells and the decrease in ICAM-I expression is directly related to the decrease in invasiveness of the pc3-GD3s cells. Another type of ER negative SK-BR3 cells exhibited the similar level of ICAM-1 expression as MDA-MB231 cells, while the ER positive MCF-7 cells (ER+) showed the increased expression level of ICAM-1. Then, we investigated signaling pathways known to control ICAM-1 expression. No difference was observed in the phosphorylation of ERK and p38 between the pc3-GD3s and control cells (pc3), but the activation of AKT was inhibited in pc3-GD3s, and not in the control (pc3). In addition, the composition of total gangliosides was changed between control (pc3) and pc3-GD3s cells, as confirmed by HPTLC. The pc3-GD3s cells had an accumulation of the GD2 instead of the GD3. RT-PCR results showed that not only GD3 synthase, but also GM2/GD2 synthase (β4-GalNc T) expression was increased in pc3-GD3s cells. Overexpression of GD3 synthase suppresses the invasive potential of human breast cancer MDA-MB-231 cells through down-regulation of ICAM-1 and the crucial pathway to allow the apoptotic effect has been attributed to accumulation of the GD2 ganglioside. ER has been linked to the ICAM-1 expression with GD3 to GD2 conversion in human breast cancer cells. This is the first finding of the endogenous sialyltransferase functions in tumor cells.

Biological roles of glycans

Simple and complex carbohydrates (glycans) have long been known to play major metabolic, structural and physical roles in biological systems. Targeted microbial binding to host glycans has also been studied for decades. But such biological roles can only explain some of the remarkable complexity and organismal diversity of glycans in nature. Reviewing the subject about two decades ago, one could find very few clear-cut instances of glycan-recognition-specific biological roles of glycans that were of intrinsic value to the organism expressing them. In striking contrast there is now a profusion of examples, such that this updated review cannot be comprehensive. Instead, a historical overview is presented, broad principles outlined and a few examples cited, representing diverse types of roles, mediated by various glycan classes, in different evolutionary lineages. What remains unchanged is the fact that while all theories regarding biological roles of glycans are supported by compelling evidence, exceptions to each can be found. In retrospect, this is not surprising. Complex and diverse glycans appear to be ubiquitous to all cells in nature, and essential to all life forms. Thus, >3 billion years of evolution consistently generated organisms that use these molecules for many key biological roles, even while sometimes coopting them for minor functions. In this respect, glycans are no different from other major macromolecular building blocks of life (nucleic acids, proteins and lipids), simply more rapidly evolving and complex. It is time for the diverse functional roles of glycans to be fully incorporated into the mainstream of biological sciences.

Water response to ganglioside GM1 surface remodelling

BACKGROUND

Gangliosides are biological glycolipids participating in rafts, structural and functional domains of cell membranes. Their headgroups are able to assume different conformations when packed on the surface of an aggregate, more lying or standing. Switching between different conformations is possible, and is a collective event. Switching can be induced, in model systems, by concentration or temperature increase, then possibly involving ganglioside-water interaction. In the present paper, the effect of GM1 ganglioside headgroup conformation on the water structuring and interactions is addressed.

METHODS

Depolarized Rayleigh Scattering, Raman Scattering, Quasielastic Neutron Scattering and NMR measurements were performed on GM1 ganglioside solutions, focusing on solvent properties.

RESULTS

All used techniques agree in evidencing differences in the structure and dynamics of solvent water on different time-and-length scales in the presence of either GM1 headgroup conformations.

CONCLUSIONS

In general, all results indicate that both the structural properties of solvent water and its interactions with the sugar headgroups of GM1 respond to surface remodelling. The extent of this modification is much higher than expected and, interestingly, ganglioside headgroups seem to turn from cosmotropes to chaotropes upon collective rearrangement from the standing- to the lying-conformation.

SIGNIFICANCE

In a biological perspective, water structure modulation could be one of the physico-chemical elements contributing to the raft strategy, both for rafts formation and persistence and for their functional aspects. In particular, the interaction with approaching bodies could be favoured or inhibited or triggered by complex-sugar-sequence conformational switch. This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo.

A therapeutic trial of human melanomas with combined small interfering RNAs targeting adaptor molecules p130Cas and paxillin activated under expression of ganglioside GD3

We previously demonstrated that focal adhesion kinase (FAK), p130Cas and paxillin are crucially involved in the enhanced malignant properties under expression of ganglioside GD3 in melanoma cells. Therefore, molecules existing in the GD3-mediated signaling pathway could be considered as suitable targets for therapeutic intervention in malignant melanoma. The aim of this study was to determine whether blockade of p130Cas and/or paxillin by RNAi suppresses melanoma growth. We found a suitable dose (40 μM siRNA, 25 μl/tumor) of the siRNA to suppress p130Cas in the xenografts generated in nu/nu mice. Based on these results, we performed intratumoral (i.t.) treatment with anti-p130Cas and/or anti-paxillin siRNAs mixed with atelocollagen as a drug delivery system in a xenograft tumor of a human melanoma cell line, SK-MEL-28. Mixture of atelocollagen (1.75%) and an siRNA (500 or 1000 pmol/tumor) was injected into the tumors every 3 days after the first injection. An siRNA against human p130Cas markedly suppressed tumor growth of the xenograft in a dose-dependent manner, whereas siRNA against human paxillin slightly inhibited the tumor growth. A control siRNA against firefly luciferase showed no effect. To our surprise, siRNA against human p130Cas (500 or 1000 pmol/tumor) combined with siRNA against human paxillin dramatically suppressed tumor growth. In agreement with the tumor suppression effects of the anti-p130Cas siRNA, reduction in Ki-67 positive cell number as well as in p130Cas expression was demonstrated by immunohistostaining. These results suggested that blockade of GD3-mediated growth signaling pathways by siRNAs might be a novel and promising therapeutic strategy against malignant melanomas, provided signaling molecules such as p130Cas and paxillin are significantly expressed in individual cases. This article is part of a Special Issue entitled "Glycans in personalised medicine" Guest Editor: Professor Gordan Lauc.

Anti-ganglioside antibodies in amyotrophic lateral sclerosis revisited

BACKGROUND

Amyotrophic Lateral Sclerosis (ALS) is a devastating neurodegenerative disorder with typical onset in the 5th- 6th decade of life. The hypothesis of an autoimmune origin of ALS receives less attention today, but immunological phenomena still seem to be involved and mechanisms such as protective autoimmunity may be important. Detection of antibodies against a variety of gangliosides has been repeatedly described in ALS-patients by several authors, but widely differing frequencies and titres have been reported. Therefore, we investigated the presence of six common antibodies with a commercially available test panel for GA1, GM1, GM2, GD1a, GD1b and GQ1b in a large group of clinically well-characterized ALS patients and compared them to a collective of 200 healthy blood donors.

METHODS

IgG and IgM antibodies to the six gangliosides asialoGM1 (GA1), GM1, GM2, GD1a, GD1b, GQ1b were determined by GanglioCombi ELISA in sera of 84 ALS patients. Results were expressed as a %-ratio of a highly positive control and categorized as negative (<30%), borderline (30-50%), moderately (50-100%) and strongly positive (>100%). The values obtained from 200 Swiss blood donors served as a reference group.

RESULTS

In twenty-two (26.2%) ALS-patients elevated anti-ganglioside antibodies could be detected: Taking all subspecific antibodies together, IgG antibodies were found in 9/84 (10.7%) and IgM in 15/84 (17.9%) patients. There was no correlation between age, gender, site of onset or survival and anti-ganglioside-positive/-negative titres in ALS-patients. No statistically significant difference in the frequency of anti-ganglioside antibodies compared to the group of healthy blood donors was found.

CONCLUSION

Even with this more comprehensive approach, anti-ganglioside antibody frequencies and patterns in our ALS cohort closely resembled the values measured in healthy controls. In accordance with other studies, we did not observe any association of a distinct ALS phenotype with elevated anti-ganglioside antibodies or an impact on survival.

The impact of the milk glycobiome on the neonate gut microbiota

Human milk is a complete source of nourishment for the infant. Exclusive breastfeeding not only sustains the infant's development but also guides the proliferation of a protective intestinal microbiota. Among the many components of milk that modulate the infant gut microbiota, the milk glycans, which comprise free oligosaccharides, glycoproteins, and glycolipids, are increasingly recognized as drivers of microbiota development and overall gut health. These glycans may display pleiotropic functions, conferring protection against infectious diseases and also acting as prebiotics, selecting for the growth of beneficial intestinal bacteria. The prebiotic effect of milk glycans has direct application to prevention of diseases such as necrotizing enterocolitis, a common and devastating disease of preterm infants. In this article, we review the impact of the human (and bovine) milk glycome on gut health through establishment of a milk-oriented microbiota in the neonate.

The pre-synaptic motor nerve terminal as a site for antibody-mediated neurotoxicity in autoimmune neuropathies and synaptopathies

The pre-synaptic motor nerve terminal is a highly complex and dynamic compartment within the lower motor neuron responsible for converting electrical signals into secreted chemicals. This self-renewing process of synaptic transmission is accomplished by the calcium-triggered fusion of neurotransmitter-containing vesicles with the plasma membrane and the subsequent retrieval and recycling of vesicle components. Besides this conventional physiological role, the highly active process of vesicle fusion and re-uptake into endosomal sorting pathways acts as a conduit for entry of a range of substances into the intracellular compartment of the motor nerve terminal. Whilst this entry portal sub-serves many vital physiological processes, such as those mediated by neurotrophin trafficking, there is also the potential for substantial pathological consequences resulting from uptake of noxious agents, including autoantibodies, viruses and toxins. These may act locally to induce disease within the nerve terminal, or traffic beyond to the motor neuron cell body and central nervous system to exert their pathological effects. This review focuses on the recent evidence that the ganglioside-rich pre-synaptic membrane acts as a binding site for potentially neurotoxic serum autoantibodies that are present in human autoimmune motor neuropathies. Autoantibodies that bind surface antigens induce membrane lytic effects, whereas their uptake attenuates local injury and transfers any potential pathological consequences to the intracellular compartment. Herein the thesis is explored that a balance exists between local injury at the exofacial leaflet of the pre-synaptic membrane and antibody uptake, which dictates the overall level and site of motor nerve injury in this group of disorders.

Membrane sialidase NEU3 is highly expressed in human melanoma cells promoting cell growth with minimal changes in the composition of gangliosides

NEU3 is a membrane sialidase specific for gangliosides. Its increased expression and implication in some cancers have been reported. Here, we analyzed NEU3 expression in malignant melanoma cell lines and its roles in the cancer phenotypes. Quantitative RT-PCR revealed that high levels of the NEU3 gene were expressed at almost equivalent levels with those in colon cancers. To examine the effects of overexpression of NEU3, NEU3 cDNA-transfectant cells were established using a melanoma cell line SK-MEL-28 and its mutant N1 lacking GD3. SK-MEL-28 sublines overexpressing both the NEU3 gene and NEU3 enzyme activity showed no changes in both cell growth and ganglioside expression, while N1 cells showed a mild increase in cell proliferation with increased phosphorylation of the EGF receptor and neo-synthesis of Gb3 after NEU3 transfection. In contrast, NEU3 silencing resulted in a definite reduction in cell growth in a melanoma line MeWo, while ganglioside patterns underwent minimal changes. Phosphorylation levels of ERK1/2 with serum stimulation decreased in the NEU3-silenced cells. All these results suggest that NEU3 is highly expressed to enhance malignant phenotypes including apoptosis inhibition in malignant melanomas.

Advances on the compositional analysis of glycosphingolipids combining thin-layer chromatography with mass spectrometry

Glycosphingolipids (GSLs), composed of a hydrophilic carbohydrate chain and a lipophilic ceramide anchor, play pivotal roles in countless biological processes, including infectious diseases and the development of cancer. Knowledge of the number and sequence of monosaccharides and their anomeric configuration and linkage type, which make up the principal items of the glyco code of biologically active carbohydrate chains, is essential for exploring the function of GSLs. As part of the investigation of the vertebrate glycome, GSL analysis is undergoing rapid expansion owing to the application of novel biochemical and biophysical technologies. Mass spectrometry (MS) takes part in the network of collaborations to further unravel structural and functional aspects within the fascinating world of GSLs with the ultimate aim to better define their role in human health and disease. However, a single-method analytical MS technique without supporting tools is limited yielding only partial structural information. Because of its superior resolving power, robustness, and easy handling, high-performance thin-layer chromatography (TLC) is widely used as an invaluable tool in GSL analysis. The intention of this review is to give an insight into current advances obtained by coupling supplementary techniques such as TLC and mass spectrometry. A retrospective view of the development of this concept and the recent improvements by merging (1) TLC separation of GSLs, (2) their detection with oligosaccharide-specific proteins, and (3) in situ MS analysis of protein-detected GSLs directly on the TLC plate, are provided. The procedure works on a nanogram scale and was successfully applied to the identification of cancer-associated GSLs in several types of human tumors. The combination of these two supplementary techniques opens new doors by delivering specific structural information of trace quantities of GSLs with only limited investment in sample preparation.

Multi-system disorders of glycosphingolipid and ganglioside metabolism

Glycosphingolipids (GSLs) and gangliosides are a group of bioactive glycolipids that include cerebrosides, globosides, and gangliosides. These lipids play major roles in signal transduction, cell adhesion, modulating growth factor/hormone receptor, antigen recognition, and protein trafficking. Specific genetic defects in lysosomal hydrolases disrupt normal GSL and ganglioside metabolism leading to their excess accumulation in cellular compartments, particularly in the lysosome, i.e., lysosomal storage diseases (LSDs). The storage diseases of GSLs and gangliosides affect all organ systems, but the central nervous system (CNS) is primarily involved in many. Current treatments can attenuate the visceral disease, but the management of CNS involvement remains an unmet medical need. Early interventions that alter the CNS disease have shown promise in delaying neurologic involvement in several CNS LSDs. Consequently, effective treatment for such devastating inherited diseases requires an understanding of the early developmental and pathological mechanisms of GSL and ganglioside flux (synthesis and degradation) that underlie the CNS diseases. These are the focus of this review.

De-N-acetyl GM3 promotes melanoma cell migration and invasion through urokinase plasminogen activator receptor signaling-dependent MMP-2 activation

We have recently discovered that de-N-acetyl GM3 [NeuNH(2)LacCer, d-GM3], a derivative of ganglioside GM3, is specifically expressed in metastatic tumor cells and that its expression correlates with an enhanced metastatic phenotype. Although the classic N-acetylated form of GM3 (NeuAcLacCer, c-GM3) is found in both normal and tumor cells, metastatic tumor cells (but not other cells) predominantly express d-GM3 (82-95% of total GM3). d-GM3 expression is mainly found in metastatic melanomas, but not in benign nevi or the majority of primary melanomas. Using metastatic (d-GM3-positive) and poorly invasive (d-GM3-negative) human melanoma cell lines, we found that d-GM3 stimulates cell migration and invasion by increasing the expression and activation of urokinase-like plasminogen activator (uPA). Further studies showed that d-GM3 activates matrix metalloproteinase-2 (MMP-2), but not MMP-9, when uPA receptor signaling is activated. These results implicate d-GM3 as a specific marker for metastatic melanoma and a novel therapeutic target for neoplastic diseases.

Ganglioside GM3 and its biological functions

Metabolism, topology, and possible mechanisms for regulation of the ganglioside GM3 content in the cell are reviewed. Under consideration are biological functions of GM3, such as involvement in cell differentiation, proliferation, oncogenesis, and apoptosis.

Immunologic glycosphingolipidomics and NKT cell development in mouse thymus

Invariant NKT cells are a hybrid cell type of Natural Killer cells and T cells, whose development is dependent on thymic positive selection mediated by double positive thymocytes through their recognition of natural ligands presented by CD1d, a nonpolymorphic, non-MHC, MHC-like antigen presenting molecule. Genetic evidence suggested that beta-glucosylceramide derived glycosphingolipids (GSLs) are natural ligands for NKT cells. N-butyldeoxygalactonojirimycin (NB-DGJ), a drug that specifically inhibits the glucosylceramide synthase, inhibits the endogenous ligands for NKT cells. Furthermore, we and others have found a beta-linked glycosphingolipid, isoglobotriaosylceramide (iGb3), is a stimulatory NKT ligand. The iGb3 synthase knockout mice have a normal NKT development and function, indicating that other ligands exist and remain to be identified. In this study, we have performed a glycosphingolipidomics study of mouse thymus, and studied mice mutants which are deficient in beta-hexosaminidase b or alpha-galactosidase A, two glycosidases that are up- and downstream agents of iGb3 turnover, respectively. Our mass spectrometry methods generated a first database for glycosphingolipids expressed in mouse thymus, which are specifically regulated by rate-limiting glycosidases. Among the identified thymic glycosphingolipids, only iGb3 is a stimulatory ligand for NKT cells, suggesting that large-scale fractionation, enrichment and characterization of minor species of glycosphingolipids are necessary for identifying additional ligands for NKT cells. Our results also provide early insights into cellular lipidomics studies, with a specific focus on the important immunological functions of glycosphingolipids.

Pathophysiological actions of neuropathy-related anti-ganglioside antibodies at the neuromuscular junction

The outer leaflet of neuronal membranes is highly enriched in gangliosides. Therefore, specific neuronal roles have been attributed to this family of sialylated glycosphingolipids, e.g. in modulation of ion channels and transporters, neuronal interaction and recognition, temperature adaptation, Ca(2+) homeostasis, axonal growth, (para)node of Ranvier stability and synaptic transmission. Recent developmental, ageing and injury studies on transgenic mice lacking subsets of gangliosides indicate that gangliosides are involved in maintenance rather than development of the nervous system and that ganglioside family members are able to act in a mutually compensatory manner. Besides having physiological functions, gangliosides are the likely antigenic targets of autoantibodies present in Guillain-Barré syndrome (GBS), a group of neuropathies with clinical symptoms of motor- and/or sensory peripheral nerve dysfunction. Antibody binding to peripheral nerves is thought to either interfere with ganglioside function or activate complement, causing axonal damage and thereby disturbed action potential conduction. The presynaptic motor nerve terminal at the neuromuscular junction (NMJ) may be a prominent target because it is highly enriched in gangliosides and lies outside the blood-nerve barrier, allowing antibody access. The ensuing neuromuscular synaptopathy might contribute to the muscle weakness in GBS patients. Several groups, including our own, have studied the effects of anti-ganglioside antibodies in ex vivo and in vivo experimental settings at mouse NMJs. Here, after providing a background overview on ganglioside synthesis, localization and physiology, we will review those studies, which clearly show that anti-ganglioside antibodies are capable of binding to NMJs and thereby can exert a variety of pathophysiological effects. Furthermore, we will discuss the human clinical electrophysiological and histological evidence produced so far of the existence of a neuromuscular synaptopathy contributing to muscle weakness in GBS patients.

Ganglioside GQ1b: efficient total synthesis and the expansion to synthetic derivatives to elucidate its biological roles

The convergent total synthesis of ganglioside GQ1b based on the "cassette approach" between the nonreducing end GQ1b-core heptasaccharide and glucosylceramide building blocks was accomplished in high overall yield. The use of a sialylalpha(2-->8)sialylalpha(2-->3)galactose sequence as the key building block enhanced the efficiency of the glycan assembly and led to preparative-scale synthesis readily applicable for large-scale preparation. In addition, a judicious choice of p-methoxybenzyl protecting groups on glucosylceramide provided a solution to the previous synthetic problems, including a decrease in the yield of the deprotection steps, and led to elevation of the total yield. Furthermore, unnatural-type GQ1b derivatives were synthesized systematically in good yields by capitalizing on a similar approach in order to elucidate their biological roles.

Ganglioside-linked terminal sialic acid moieties on murine macrophages function as attachment receptors for murine noroviruses

Noroviruses are the major cause of nonbacterial gastroenteritis in humans. However, little is known regarding the norovirus life cycle, including cell binding and entry. In contrast to human noroviruses, the recently discovered murine norovirus 1 (MNV-1) readily infects murine macrophages and dendritic cells in culture. Many viruses, including the related feline calicivirus, use terminal sialic acids (SA) as receptors for infection. Therefore, we tested whether SA moieties play a role during MNV-1 infection of murine macrophages. Competition with SA-binding lectins and neuraminidase treatment led to a reduction in MNV-1 binding and infection in cultured and primary murine macrophages, suggesting a role for SA during the initial steps of the MNV-1 life cycle. Because SA moieties can be attached to glycolipids (i.e., gangliosides), we next determined whether MNV-1 uses gangliosides during infection. The gangliosides GD1a, GM1, and asialo-GM1 (GA1) are natural components of murine macrophages. MNV-1 bound to ganglioside GD1a, which is characterized by an SA on the terminal galactose, but not to GM1 or asialo-GM1 in an enzyme-linked immunosorbent assay. The depletion of gangliosides using an inhibitor of glycosylceramide synthase (d-threo-P4) led to a reduction of MNV-1 binding and infection in cultured and primary murine macrophages. This defect was specifically rescued by the addition of GD1a. A similar phenotype was observed for MNV field strains WU11 (GV/WU11/2005/USA) and S99 (GV/Berlin/2006/DE). In conclusion, our data indicate that MNV can use terminal SA on gangliosides as attachment receptors during binding to murine macrophages.

Glycosyltransferase B4GALNT1 and type 1 diabetes in Croatian population: clinical investigation

OBJECTIVES

Type 1 diabetes mellitus (T1DM) is an autoimmune disease characterized by destruction of pancreatic beta cells. Gangliosides are thought to be a target of a variety of anti-islet autoantibodies. The formation of gangliosides is catalyzed by addition of sugar residues to complex glycoconjugate molecules by glycosyltransferases. Beta-1,4-N-acetyl-galactosaminyl transferase 1 is the enzyme involved in the synthesis of asialo, a, b and c-series gangliosides and it is coded by B4GALNT1 gene.

DESIGN AND METHODS

We genotyped 2 B4GALNT1 tagSNPs, designed to capture 100% of common variation in the region, in 202 families and 199 controls from the Croatian population.

RESULTS

Transmission disequilibrium test and case-control analysis did not detect an association of B4GALNT1 gene with T1DM.

CONCLUSIONS

Expression of gangliosides requires coordinated work of many genes. There is enough evidence showing that gangliosides are plausible contributors to T1DM pathological processes and, therefore, future studies on different glycosyltransferase genes are necessary.

Expression of ganglioside GT1b in mouse embryos at different developmental stages after cryopreservation

Gangliosides are a family of sialic acid-containing glycosphingolipids that are abundant in neurons and have a variety of functions in developing and mature tissues. We examined the expression of ganglioside GT1b in the embryonic preimplantation stage after freezing and thawing processes to determine the regulatory roles of ganglioside GT1b in early embryonic development. ICR mouse embryos at the two-cell stage obtained by flushing the oviducts were frozen by two cryopreservation procedures, slow freezing using a programmable freezer or vitrification by direct plunging into liquid nitrogen. Slow freezing was conducted with equilibration in 1.5 M 1,2-propanediol or 5% equilibration glycerol. Vitrification was applied with a 10-15 min equilibration in 7.5% ethylene glycol (EG), 7.5% dimethylsulfoxide (DMSO), and 30 sec in a solution of 15% EG, 15% DMSO and 0.5 M sucrose. Immediately after thawing, the survival rate of the embryos was assessed by their morphology and ability to develop to blastocysts in culture. The survival rate of vitrified and thawed embryos (92%) was significantly higher than that of slow frozen and thawed embryos (76%) (P<0.05). A tendency of higher blastocyst rate was found in the vitrified and thawed embryos compared to that of the slow frozen and thawed embryos. Confocal immunofluorescence staining confirmed that surviving embryos expressed ganglioside GT1b, with the strongest expression at the compacted eight-cell or later stage embryos. Ganglioside GT1b was not observed in the TUNEL-positive, apoptotic embryos, suggesting that cryopreservation had induced DNA breaks in them. These results suggest that ganglioside GT1b may play an important role in embryo survival or development.

Structural transition of a 15 amino acid residue peptide induced by GM1

The ganglioside GM1-binding peptide, p3, with a sequence of VWRLLAPPFSNRLLP, displayed a clear structural alteration depending on the presence or absence of GM1 micelles. The three-dimensional structures of the p3 peptide in the free and GM1 bound states were analyzed using two-dimensional NMR spectroscopic experiments with distance-restrained simulated annealing calculations. The NMR experiments for the p3 peptide alone indicated that the peptide has two conformers derived from the exchange of cis and trans forms at Pro(7)-Pro(8). Further study with theoretical modeling revealed that the p3 peptide has a curb conformation without regular secondary structure. On the other hand, the NMR studies for the p3 peptide with the GM1 micelles elucidated a trans conformer and gave a structure stabilized by hydrophobic interactions of beta- and helical turns. Based on these structural investigations, tryptophan, a core residue of the hydrophobic cluster, might be an essential residue for the recognition of the GM1 saccharides. The dynamic transition of the p3 peptide may play an important role in the function of GM1 as a multiple receptor as in the traditional pathway of the infection by cholera toxin.

Structural Analysis of the α-2,3-Sialyltransferase Cst-I from Campylobacter jejuni in Apo and Substrate-Analogue Bound Forms,

Sialic acid is an essential sugar in biology that plays key roles in numerous cellular processes and interactions. The biosynthesis of sialylated glycoconjugates is catalyzed by five distinct families of sialyltransferases. In the last 25 years, there has been much research on the enzymes themselves, their genes, and their reaction products, but we still do not know the precise molecular mechanism of action for this class of glycosyltransferase. We previously reported the first detailed structural and kinetic characterization of Cst-II, a bifunctional sialyltransferase (CAZy GT-42) from the bacterium Campylobacter jejuni [Chiu et al. (2004) Nat. Struct. Mol. Biol. 11, 163-170]. This enzyme can use both Gal-beta-1,3/4-R and Neu5Ac-alpha-2,3-Gal-beta-1,3/4-R as acceptor sugars. A second sialyltransferase from this bacterium, Cst-I, has been shown to utilize solely Gal-beta-1,3/4-R as the acceptor sugar in its transferase reaction. We report here the structural and kinetic characterization of this monofunctional enzyme, which belongs to the same sialyltransferase family as Cst-II, in both apo and substrate bound form. Our structural data show that Cst-I adopts a similar GTA-type glycosyltransferase fold to that of the bifunctional Cst-II, with conservation of several key noncharged catalytic residues. Significant differences are found, however, between the two enzymes in the lid domain region, which is critical to the creation of the acceptor sugar binding site. Furthermore, molecular modeling of various acceptor sugars within the active sites of these enzymes provides significant new insights into the structural basis for substrate specificities within this biologically important enzyme class.

Evaluation of SAT-1, SAT-2 and GalNAcT-1 mRNA in colon cancer by real-time PCR

By qualitative and quantitative PCR, we evaluated the expression of three messengers coding for SAT-1, SAT-2 and GalNAcT-1 in human samples of intestinal cancer and some cell lines (breast cancer and melanomas). Qualitative PCR demonstrated, in human tissues but not in the cell lines examined, the presence of an mRNA that lacks hexon 3; experiments performed on transfected SKMEL-28 excluded a regulative role of this noncanonical mRNA. Data from real-time PCR, statistically analysed by ANOVA indicated that the mRNA expression of all the considered glycosyltransferases (SAT-1, SAT-2 and GalNAcT-1) was significantly different in tumours versus their own control. The ganglioside patterns in the examined samples did not correlate with mRNA expression; this finding demonstrates that ganglioside expression is the result of a very complex balance between anabolic and catabolic enzyme activities. Although this study is still preliminary, it opens a new possibility for neoplastic prognosis finding potential molecular markers among the mRNAs that codify for glycosyltransferases.

Molecular cloning and expression of alpha2,8-sialyltransferase (ST8Sia I, GD3 Synthase) in Xenopus

GD3, a minor ganglioside in most normal tissues, is involved in important biological events and its expression could increase in pathological conditions. Organism integrity requires a tight balance between the anabolic and catabolic processes, thus it is important to control the intracellular expression of those "key" enzymes, which act at the "branching point" of ganglioside metabolism; one of these is the GD3-synthase (ST8Sia I). In this paper, we report the sequences of two ST8Sia I mRNAs found in Xenopus laevis and their genomic organization; the canonical form resulted constituted of 5 exons and 4 introns, while the "short" mRNA lacks of the exon 2. The expression of the two ST8Sia I mRNAs during embryo development and their tissue distribution in adult animals showed the single or simultaneous presence of the two forms. Experiments of in vitro expression and evaluation of enzymatic activity of the two hypothetical proteins turned out to be ST8Sia I. In the end, considering the growing interest toward the specie Xenopus tropicalis, due to its diploid genome that render it more suitable for genetic studies, we also cloned X. tropicalis ST8Sia I.

The role of sialic acid in human polyomavirus infections

JC virus (JCV) and BK virus (BKV) are human polyomaviruses that infect approximately 85% of the population worldwide [1,2]. JCV is the underlying cause of the fatal demyelinating disease, progressive multifocal leukoencephalopathy (PML), a condition resulting from JCV induced lytic destruction of myelin producing oligodendrocytes in the brain [3]. BKV infection of kidneys in renal transplant recipients results in a gradual loss of graft function known as polyomavirus associated nephropathy (PVN) [4]. Following the identification of these viruses as the etiological agents of disease, there has been greater interest in understanding the basic biology of these human pathogens [5,6]. Recent advances in the field have shown that viral entry of both JCV and BKV is dependent on the ability to interact with sialic acid. This review focuses on what is known about the human polyomaviruses and the role that sialic acid plays in determining viral tropism.

Glycolipids from a colloid chemical point of view

Glycolipids are a group of compounds with a broad range of applications. Two types of glycolipids (alkylpolyglycosides and gangliosides) were examined with regard to their physicochemical properties. Despite their structural differences, they have in common that they are amphiphilic molecules and able to aggregate to form monolayers, bilayers, micelles, lyothropic mesophases or vesicles. The structures of glycolipid micelles were investigated by different experimental techniques in addition to molecular dynamic simulations. The knowledge of the physicochemical properties of gangliosides enables a better understanding of their biological functions. Structural features were obtained for the monosialogangliosides GM1, GM2 and GT1b from bovine brain by means of mass spectrometry. Further the aggregation behaviour was determined by small-angle neutron and dynamic light scattering experiments. Interaction studies of these compounds were carried out by means of surface plasmon resonance using gangliosides incorporated liposomes. They were used as model membranes that interact with the lectins WGA, RCA and HPA. The interaction of lectins immobilized to a modified silicon surface was investigated by in-situ ellipsometry.

The immunoregulatory effects of gangliosides involve immune deviation favoring type-2 T cell responses

Gangliosides, sialic acid-containing glycosphingolipids present in most cell membranes, are thought to participate in the maintenance of immune privilege and tumor-induced immunosuppression. However, the mechanisms responsible for their immunomodulatory activity remain poorly understood. The purpose of this study was to investigate whether gangliosides are able to modulate the balance of type-1/type-2 T cell responses and to characterize the cellular mechanisms involved. The effects of different gangliosides on anti-CD3-stimulated murine splenocytes and purified T cells were studied. The presence of gangliosides during T cell activation reduced the expression of interferon-gamma (IFN-gamma) and enhanced that of interleukin (IL)-4, suggesting a shift toward a type-2 response. Intracellular cytokine staining demonstrated that gangliosides inhibited IFN-gamma production in CD4+, CD8+, and natural killer (NK)1.1+ cell populations and enhanced IL-4 in CD4+ T cells. The ganglioside-mediated enhancement in IL-4 production was independent of changes in endogenous IFN-gamma, did not occur with cells from CD1d-deficient mice, and was partially inhibited by anti-CD1d antibodies. The inhibitory effects on IFN-gamma were independent of endogenous IL-4 or the presence of NKT cells and were unaffected by anti-CD1d antibodies. These results suggest that gangliosides may modify the immunological environment by promoting immune deviation in favor of type-2 T cell responses.

Facile method for the preparation of lyso-GM1 and lyso-GM2

This paper reports a facile method for the preparation of lyso-GM1 [Gal beta1-->3GalNAc beta1--> 4(Neu5Ac alpha2-->3)Galbeta1-->4Glc beta1-->1'-sphingosine] and lyso-GM2 [GalNAc beta1-->4(Neu5Ac alpha2-->3)Gal beta1-->4Glc beta1-->sphingosine], respectively, from GM1 [Galbeta1-->3GalNAc beta1-->4(Neu5Ac alpha2-->3)Galbeta1-->4Glc beta1-->1'-Cer] and GM2[GalNAc beta1-->4(Neu5Ac alpha2-->3)Galbeta1-->4Glc beta1-->1'-Cer], using sphingolipid ceramide deacylase and high performance anion-exchange chromatography (HPAEC). The enzymatically released lyso-GM1 and/or lyso-GM2 was effectively separated from its parent ganglioside by HPAEC using a Mono Q HR 5/5 column with an Amersham Biosciences fast protein liquid chromatography system. The yield was almost quantitative and the separation completed in approximately 3 h. This method is more convenient and effective than the conventional method using alkaline hydrolysis and silicic acid chromatography to generate and purify lyso-gangliosides.

Thyroid sialyltransferase mRNA level and activity are increased in Graves' disease

Sialylation of cell components is an important immunomodulating mechanism affecting cell response to hormones and adhesion molecules. To study alterations in sialic acid metabolism in Graves' disease (GD) we measured the following parameters in various human thyroid tissues: lipid-bound sialic acid (LBSA) content, ganglioside profile, total sialyltransferase activity, and the two major sialyltransferase mRNAs for sialyltransferase-1 (ST6Gal I) and for sialyltransferase-4A (ST3Gal I). Fragments of toxic thyroid nodules (TN), nontoxic thyroid nodules (NN) and nontumorous tissue from patients with nodular goiter or thyroid cancer were used as a control (C). The LBSA content and sialyltransferase activity were the highest in the GD group (164 +/- 4.44 versus 120 +/- 2.00 nmoL/g, p = 0.005 and 1625 +/- 283.5 versus 324 +/- 54.2 cpm/mg of protein, p < 0.005 compared to control group C). Ganglioside profile in the GD group was similar to that in control tissues. Sialyltransferase- 1 mRNA and sialyltransferase-4A mRNA levels were significantly higher in the GD group than in the control group (12.52 +/- 6.90 versus 2.54 +/- 1.24 arbitrary units, p < 0.005 and 2,49 +/- 1.16 versus 1.23 +/- 0.46 arbitrary units, p < 0.05, respectively). There was a positive correlation between the increased sialyltransferase-1 mRNA level and the TSH-receptor antibody titer determined by the TRAK test. These results indicate that sialyltransferases expression and activity are increased in GD. Exact mechanism of this upregulation remains unknown, though one of possible explanations is the activation of the thyrotropin (TSH) receptor.

human and bovine milk gangliosides differ in their fatty acid composition

Gangliosides are considered bioactive components in human infant nutrition, and their fatty acid composition alters their biological effects. We used matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) MS and GLC to analyze the fatty acid composition of the predominant gangliosides, the monosialoganglioside GM(3) [sialic acid (Sia) alpha2-3 galactose (Gal) beta1-4 glucose (Glc) beta1-1 ceramide] and the disialoganglioside GD(3) (Sia alpha2-8 Sia alpha2-3 Gal beta1-4 Glc beta1-1 ceramide), in pooled human and bovine milk, the latter being a source for gangliosides in infant formula. Compared with whole milk lipids, both human and bovine milk gangliosides were selectively enriched with certain fatty acids, and the fatty acid composition of milk gangliosides in the 2 species was significantly different. The amount of long-chain fatty acids (> or =20 C atoms) was higher in bovine milk gangliosides (GM(3): 73.71 +/- 3.39%; GD(3): 79.19 +/- 2.79%) than in human milk gangliosides (GM(3): 51.25 +/- 0.65%; GD(3): 34.04 +/- 1.80%). Tricosanoic acid (23:0) dominated in bovine milk gangliosides (GM(3): 24.05 +/- 1.37%; GD(3): 26.66 +/- 1.24%), whereas it only played a minor role in human milk gangliosides (GM(3): 2.88 +/- 0.10%; GD(3): 1.84 +/- 0.29%). We hypothesized that the differences in the fatty acid composition of milk gangliosides result in physiological distinctions between breast-fed and formula-fed infants and therefore are of importance for human infant nutrition.

Sialic acid residues on astrocytes regulate neuritogenesis by controlling the assembly of laminin matrices

In the developing nervous system migrating neurons and growing axons are guided by diffusible and/or substrate-bound cues, such as extracellular matrix-associated laminin. In a previous work we demonstrated that laminin molecules could self-assemble in two different manners, giving rise to matrices that could favor either neuritogenesis or proliferation of cortical precursor cells. We investigated whether the ability of astrocytes to promote neuritogenesis of co-cultivated neurons was modulated by the assembling mode of the laminin matrix secreted by them. We compared the morphologies and neuritogenic potentials of laminin deposited by in vitro-differentiated astrocytes obtained from embryonic or neonatal rat brain cortices. We showed that, while permissive astrocytes derived from embryonic brain produced a flat laminin matrix that remained associated to the cell surface, astrocytes derived from newborn brain secreted a laminin matrix resembling a fibrillar web that protruded from the cell plane. The average neurite lengths obtained for E16 neurons cultured on each astrocyte layer were 198+/-22 and 123+/-13 microm, respectively. Analyses of surface-associated electrostatic potentials revealed that embryonic astrocytes presented a pI of -2.8, while in newborn cells this value was -3.8. Removal of the sialic acid groups on the embryonic monolayer by neuraminidase treatment led to the immediate release of matrix-associated laminin. Interestingly, laminin reassembled 1 hour after neuraminidase removal converted to the features of the newborn matrix. Alternatively, treatment of astrocytes with the cholesterol-solubilizing detergent methyl-beta-cyclodextrin also resulted in release of the extracellular laminin. To test the hypothesis that sialic-acid-containing lipids localized at cholesterol-rich membrane domains could affect the process of laminin assembly, we devised a cell-free assay where laminin polymerization was carried out over artificial lipid films. Films of either a mixture of gangliosides or pure ganglioside GT1b induced formation of matrices of morpho-functional features similar to the matrices deposited by embryonic astrocytes. Conversely, films of phosphatidylcholine or ganglioside GM1 led to the formation of bulky laminin aggregates that lacked a defined structure. We propose that the expression of negative lipids on astrocytes can control the extracellular polymerization of laminin and, consequently, the permissivity to neuritogenesis of astrocytes during development.

Overexpressed GM1 Suppresses Nerve Growth Factor (NGF) Signals by Modulating the Intracellular Localization of NGF Receptors and Membrane Fluidity in PC12 Cells

Ganglioside GM1 has been considered to have a neurotrophic factor-like activity. To analyze the effects of endogenously generated GM1, the rat pheochromocytoma cell line PC12 was transfected with the GM1/GD1b/GA1 synthase gene and showed increased expression levels of GM1. To our surprise, GM1+-transfectant cells (GM1+ cells) showed no neurite formation after stimulation with nerve growth factor (NGF). Autophosphorylation of NGF receptor TrkA and activation of ERK1/2 after NGF treatment were scarcely detected in GM1+ cells. Binding of 125I-NGF to PC12 cells was almost equivalent between GM1+ cells and controls. However, dimer formation of TrkA upon NGF treatment was markedly suppressed in GM1+ cells in both cross-linking analysis with Bis(sulfosuccinimidyl)suberate 3 and 125I-NGF binding assay. The sucrose density gradient fractionation of the cell lysate revealed that TrkA primarily located in the lipid raft fraction moved to the non-raft fraction in GM1+ cells. p75NTR and Ras also moved from the raft to non-raft fraction in GM1+ cells, whereas flotillin and GM1 persistently resided in the lipid raft. TrkA kinase activity was differentially regulated when GM1 was added to the kinase assay system in vitro, suggesting suppressive/enhancing effects of GM1 on NGF signals based on the concentration. Measurement of fluorescence recovery after photobleaching revealed that the membrane fluidity was reduced in GM1+ cells. These results suggested that overexpressed GM1 suppresses the differentiation signals mediated by NGF/TrkA by modulating the properties of the lipid raft and the intracellular localization of NGF receptors and relevant signaling molecules.

Bioengineering of Surface GD3 Ganglioside for Immunotargeting Human Melanoma Cells

N-Propionyl, N-butyryl (N-Bu), and N-benzoyl mannosamine, as precursors of sialic acid biosynthesis, were incubated with human melanoma SK-MEL-28 cells and resulted in the replacement of N-acetyl groups on the cell surface sialic acid residues, including those associated with GD3. Meanwhile, vaccines containing GD3 and modified GD3 tetrasaccharide-keyhole limpet hemocyanin conjugates were synthesized, and BALB/c mice were immunized with them together with monophosphoryl lipid A adjuvant. The GD3Bu-keyhole limpet hemocyanin conjugate raised the highest IgG titers without any cross-reactivity to unmodified GD3. Expression of GD3Bu epitopes on the surface of SK-MEL-28 cells was confirmed in vitro and in vivo by the binding of a polyclonal antiserum and monoclonal antibody (mAb) 2A, both of which specifically recognize GD3Bu, and by mass spectroscopic analysis of glycolipids extracted from cells. Following expression of GD3Bu on the surface of SK-MEL-28 cells, the cells could be lysed by mAb 2A and GD3Bu antiserum in the presence of complement. Although less effective in the control of existing large size tumors ( approximately 10 mm inner diameter) on BALB/c nu/nu mice, mAb 2A in combination with ManNBu effectively protected mice from SK-MEL-28 tumor grafting. This approach may provide a method to augment the immunogenicity of sialylated human antigens and to avoid generating an autoimmune response to them at same time.

Structural analysis of the sialyltransferase CstII from Campylobacter jejuni in complex with a substrate analog

Sialic acid terminates oligosaccharide chains on mammalian and microbial cell surfaces, playing critical roles in recognition and adherence. The enzymes that transfer the sialic acid moiety from cytidine-5'-monophospho-N-acetyl-neuraminic acid (CMP-NeuAc) to the terminal positions of these key glycoconjugates are known as sialyltransferases. Despite their important biological roles, little is understood about the mechanism or molecular structure of these membrane-associated enzymes. We report the first structure of a sialyltransferase, that of CstII from Campylobacter jejuni, a highly prevalent foodborne pathogen. Our structural, mutagenesis and kinetic data provide support for a novel mode of substrate binding and glycosyl transfer mechanism, including essential roles of a histidine (general base) and two tyrosine residues (coordination of the phosphate leaving group). This work provides a framework for understanding the activity of several sialyltransferases, from bacterial to human, and for the structure-based design of specific inhibitors.

Expression of glycosphingolipids in lymph nodes of mice lacking TNF receptor 1: biochemical and flow cytometry analysis

The expression of gangliosides and neutral glycosphingolipids (GSLs) in the lymph nodes of mice lacking the gene for the tumour necrosis factor-alpha receptor p55 (TNFR1) has been investigated. GSL expression in the tissues of mice homozygous (TNFR1-/-) or heterozygous (TNFR1+/-) for the gene deletion was analysed by flow cytometry and high-performance thin-layer chromatography (HPTLC) followed by immunostaining with specific antibodies. HPTLC immunostaining revealed that lymph nodes from TNFR1-/- mice had reduced expression of ganglioside GM1b and GalNAc-GM1b, neolacto-series gangliosides, as well as the globo- (Gb3, Gb4 and Gb5) and ganglio-series (Gg3 and Gg4) neutral GSLs. Flow cytometry of freshly isolated lymph node cells showed no significant differences in GSL expression, except for the GalNAc-GM1b ganglioside, which was less abundant on T lymphocytes from TNFR1-/- lymph nodes. In TNFR1-/- mice, GalNAc-GM1b+/CD4+ T cells were twofold less abundant (3.8% vs 7.6% in the control mice), whereas GalNAc-GM1b+/CD8+ T cells were fourfold less abundant (5.0% vs 20.2% in the control mice). This study provides in vivo evidence that TNF signalling via the TNFR1 is important for the activation of GM1b-type ganglioside biosynthetic pathway in CD8 T lymphocytes, suggesting its possible role in the effector T lymphocyte function.

Localization of ganglioside 9-O-acetyl GD3 in point contacts of neuronal growth cones

Gangliosides are a large group of sialylated glycosphingolipids widely expressed in mammalian tissues. We have shown previously that the expression of 9-O-acetyl GD3 is highly correlated with periods of neurite outgrowth in the developing nervous system, and that the advance of dorsal root ganglia growth cones on laminin was halted in presence of an antibody specific for 9-O-acetyl GD3. In this work, we examined by immunocytochemistry and confocal microscopy whether this ganglioside is localized in point contacts in neuronal growth cones. We identified point contacts by immunoreactions with proteins, such as vinculin and beta1 integrin, known to be associated with these structures in growth cones. Our observations indicate that 9-O-acetyl GD3 is specifically associated with vinculin and beta1 integrin in point contacts of growth cones, suggesting a possible role for this particular ganglioside in the modulation of these contacts during neurite outgrowth.

Functional role of a specific ganglioside in neuronal migration and neurite outgrowth

Cell migration occurs extensively during mammalian brain development and persists in a few regions in the adult brain. Defective migratory behavior of neurons is thought to be the underlying cause of several congenital disorders. Knowledge of the dynamics and molecular mechanisms of neuronal movement could expand our understanding of the normal development of the nervous system as well as help decipher the pathogenesis of neurological developmental disorders. In our studies we have identified and characterized a specific ganglioside (9-O-acetyl GD3) localized to the membrane of neurons and glial cells that is expressed in regions of cell migration and neurite outgrowth in the developing and adult rat nervous system. In the present article we review our findings that demonstrate the functional role of this molecule in neuronal motility.

Chemical and enzymatic transacylation of amide-linked FA of buttermilk gangliosides

The goal of this work was to alter the composition of amide-linked FA of bovine buttermilk gangliosides, particularly the disialoganglioside GD3, to adjust lipid sources to special food specifications and pharmacological or cosmetic applications. The chemical transacylation of amide-linked FA of buttermilk gangliosides with free arachidic acid (20:0) by a combination of basic hydrolysis and diethylphosphorylcyanide/triethylamine-catalyzed reacylation was compared to an enzymatic sphingolipid ceramide N-deacylase (EC 3.5.1.23)-catalyzed FA exchange by GC analysis and nano electrospray ionization-MS. The buttermilk predominantly contained the disialoganglioside GD3 and the monosialoganglioside GM3. The heterogeneity of FA that are incorporated into gangliosides, mainly palmitic acid (29.4 wt%), stearic acid (16.9 wt%), oleic acid (17.8 wt%), and myristic acid (8.5 wt%), was effectively altered by both transesterification techniques. Arachidic acid, which was not integrated into the initial buttermilk gangliosides, was transacylated to total gangliosides with 23.2 wt% (GD3, 6.7 wt%) by the chemical process and with 8.7 wt% (GD3, 13.8 wt%) when catalyzed enzymatically. Mainly behenic acid and lignoceric acid of GD3 were exchanged chemically, and stearic acid was exchanged by the enzymatic process. This observation might depend on hydrolytic sensitivities of amide-linked very long chain saturated FA or specific enzyme subtrate affinities, respectively. Results of chemical hydrolysis indicated there was a risk of sialic acid decomposition and unspecific degradations. Regarding specificity and avoidance of critical agents, the enzymatic transesterification is recommended for industrial-scale production of consumer goods.