Polyglycosylceramides, Poly-N-acetyllactosamine-Containing Glycosphingolipids: Methods of Analysis, Structure, and Presumable Biological Functions

Divergence in metabolomic profile in clownfish and damselfish skin mucus

Introduction

The clownfish - sea anemone mutualism was suggested to have triggered the adaptive radiation of clownfishes, but the origin of clownfish resistance to stinging tentacles of host anemones remains unclear. The presence of specific compounds in the mucus of clownfishes conferring them the unique ability to prevent nematocyst discharge from their hosts has been the most supported hypothesis. Yet the mystery regarding the types of compounds found in clownfish skin mucus remains unsolved.

Methods

We analyzed the chemical composition of clownfish and damselfish mucus using an untargeted metabolomics (HILIC-HRMS) and lipidomics (RPLC-HRMS) approach.

Results and Discussion

The polar and lipid metabolome signatures were highly specific and allowed to discriminate between the clownfish and damselfish clades. The most discriminative part of the signature was the sphingolipid profile, displaying a broader diversity of ceramides present in significantly higher levels in clownfish mucus. Importantly, the inter-specific variability of metabolic signature was significantly higher in clownfishes, although their diversification is evolutionarily more recent, thus implying the impact of symbiosis on metabolic variability and adaptation. Furthermore, specialists and generalists clownfish species displayed distinctive metabolite signature. Two strict clownfish specialists, which are phylogenetically distant but share the same host species, clustered together based on their molecular signature, suggesting a link with their mutualistic nature. Overall, comparative analyses of metabolic signatures highlight differences in chemical composition of clownfish mucus and provide insight into biochemical pathways potentially implicated in clownfish adaptation to inhabit sea anemones and consequently diversify.

Shiga toxin-glycosphingolipid interaction: Status quo of research with focus on primary human brain and kidney endothelial cells

Shiga toxin (Stx)-mediated injury of the kidneys and the brain represent the major extraintestinal complications in humans upon infection by enterohemorrhagic Escherichia coli (EHEC). Damage of renal and cerebral endothelial cells is the key event in the pathogenesis of the life-threatening hemolytic uremic syndrome (HUS). Stxs are AB₅ toxins and the B-pentamers of the two clinically important Stx subtypes Stx1a and Stx2a preferentially bind to the glycosphingolipid globotriaosylceramide (Gb3Cer, Galα4Galβ4Glcβ1Cer) and to less extent to globotetraosylceramide (Gb4Cer, GalNAcβ3Galα4Galβ4Glcβ1), which are expected to reside in lipid rafts in the plasma membrane of the human endothelium. This review summarizes the current knowledge on the Stx glycosphingolipid receptors and their lipid membrane ensemble in primary human brain microvascular endothelial cells (pHBMECs) and primary human renal glomerular endothelial cells (pHRGECs). Increasing knowledge on the precise initial molecular mechanisms by which Stxs interact with cellular targets will help to develop specific therapeutics and/or preventive measures to combat EHEC-caused diseases.

Colocalization of receptors for Shiga toxins with lipid rafts in primary human renal glomerular endothelial cells and influence of D-PDMP on synthesis and distribution of glycosphingolipid receptors

Damage of human renal glomerular endothelial cells (HRGECs) of the kidney represents the linchpin in the pathogenesis of the hemolytic uremic syndrome caused by Shiga toxins of enterohemorrhagic Escherichia coli (EHEC). We performed a comprehensive structural analysis of the Stx-receptor glycosphingolipids (GSLs) globotriaosylceramide (Gb3Cer, Galα4Galβ4Glcβ1Cer) and globotetraosylceramide (Gb4Cer, GalNAcβ3Galα4Galβ4Glcβ1Cer) and their distribution in lipid raft analog detergent-resistant membranes (DRMs) and nonDRMs prepared from primary HRGECs. Predominant receptor lipoforms were Gb3Cer and Gb4Cer with Cer (d18:1, C16:0), Cer (d18:1, C22:0) and Cer (d18:1, C24:1/C24:0). Stx-receptor GSLs co-distribute with sphingomyelin (SM) and cholesterol as well as flotillin-2 in DRMs, representing the liquid-ordered membrane phase and indicating lipid raft association. Lyso-phosphatidylcholine (lyso-PC) was identified as a nonDRM marker phospholipid of the liquid-disordered membrane phase. Exposure of primary HRGECs to the ceramide analogon d-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP) reduced total Gb3Cer and Gb4Cer content, roughly calculated from two biological replicates, down to half and quarter of its primordial content, respectively, but strengthened their prevalence and cholesterol preponderance in DRMs. At the same time, the distribution of PC, SM and lyso-PC to subcellular membrane fractions remained unaffected by D-PDMP treatment. Defining the GSL composition and precise microdomain structures of primary HRGECs may help to develop novel therapeutic options to combat life-threatening EHEC infections.

Shiga Toxin Glycosphingolipid Receptors in Human Caco-2 and HCT-8 Colon Epithelial Cell Lines

Shiga toxins (Stxs) released by enterohemorrhagic Escherichia coli (EHEC) into the human colon are the causative agents for fatal outcome of EHEC infections. Colon epithelial Caco-2 and HCT-8 cells are widely used for investigating Stx-mediated intestinal cytotoxicity. Only limited data are available regarding precise structures of their Stx receptor glycosphingolipids (GSLs) globotriaosylceramide (Gb3Cer) and globotetraosylceramide (Gb4Cer), and lipid raft association. In this study we identified Gb3Cer and Gb4Cer lipoforms of serum-free cultivated Caco-2 and HCT-8 cells, chiefly harboring ceramide moieties composed of sphingosine (d18:1) and C16:0, C22:0 or C24:0/C24:1 fatty acid. The most significant difference between the two cell lines was the prevalence of Gb3Cer with C16 fatty acid in HCT-8 and Gb4Cer with C22–C24 fatty acids in Caco-2 cells. Lipid compositional analysis of detergent-resistant membranes (DRMs), which were used as lipid raft-equivalents, indicated slightly higher relative content of Stx receptor Gb3Cer in DRMs of HCT-8 cells when compared to Caco-2 cells. Cytotoxicity assays revealed substantial sensitivity towards Stx2a for both cell lines, evidencing little higher susceptibility of Caco-2 cells versus HCT-8 cells. Collectively, Caco-2 and HCT-8 cells express a plethora of different receptor lipoforms and are susceptible towards Stx2a exhibiting somewhat lower sensitivity when compared to Vero cells.

Sequential one-pot enzymatic synthesis of oligo-N-acetyllactosamine and its multi-sialylated extensions

A simple and efficient protocol for the preparative-scale synthesis of various lengths of oligo-N-acetyllactosamine (oligo-LacNAc) and its multi-sialylated extensions.

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.

Recent advances in the glycosylation of sphingosines and ceramides

Glycosphingolipids (GSLs) are ubiquitous components of eukaryotic cell membranes. They are highly bioactive and are involved in many aspects of cell signalling like cell-cell interaction, cell-substratum interaction and cell-pathogen interaction. GSLs also are involved in the modulation of signal transduction, resulting in regulation of cell proliferation and differentiation. The biological importance and complexity of these compounds afford many opportunities to prepare synthetic analogues for studies of their metabolism in intra- and intercellular processes. This review focuses on recent contributions in the synthesis of GSLs, highlighting improvements in glycosylation reactions leading to alpha and beta glycosyl sphingosines and ceramides and related compounds. Literature from 2000 to the present is covered. The glycosylation reactions leading to the synthesis of GSLs are classified in function of the configuration of the created glycosidic bond (alpha or beta) and of the acceptor used, either azido-sphingosine or ceramide.

Novel glycolipid variations revealed by monoclonal antibody immunochemical analysis of weak ABO subgroups of A

BACKGROUND AND OBJECTIVES

The chemical basis of the subgroups of A is largely unknown. We used thin-layer chromatography immunochemical staining techniques together with a range of characterized monoclonal reagents to analyse glycolipids isolated from a variety of weak subgroups.

MATERIALS AND METHODS

Glycolipids isolated from red cells collected from nine genetically defined individuals of the rare subgroups of A, including a novel A(3) allele (A(2) 539G>A) not described previously, were subjected to a highly sensitive thin-layer chromatographic immunochemical analysis.

RESULTS

Semicharacterized monoclonal antibodies revealed that, in addition to the expected quantitative differences between common phenotypes and the weak subgroups, qualitative glycolipid differences (or at least an apparent qualitative basis), caused by major changes in the ratios of different structures exist. Specifically it was found that the weakest A-expressing samples (A(el) phenotype) appeared to express an unusual A structure in the 8-12 sugar region. Variable expression of several structures in one of the A weak samples were suggestive of novel blood group A structures.

CONCLUSIONS

Although no structural characterization could be undertaken, the results are clearly indicative that the variant glycosyltransferases of the rare ABO subgroups are not only inefficient, but they may potentially synthesize novel ABO structures.

Glycosphingolipid structural analysis and glycosphingolipidomics

Sphingosines, or sphingoids, are a family of naturally occurring long-chain hydrocarbon derivatives sharing a common 1,3-dihydroxy-2-amino-backbone motif. The majority of sphingolipids, as their derivatives are collectively known, can be found in cell membranes in the form of amphiphilic conjugates, each composed of a polar head group attached to an N-acylated sphingoid, or ceramide. Glycosphingolipids (GSLs), which are the glycosides of either ceramide or myo-inositol-(1-O)-phosphoryl-(O-1)-ceramide, are a structurally and functionally diverse sphingolipid subclass; GSLs are ubiquitously distributed among all eukaryotic species and are found in some bacteria. Since GSLs are secondary metabolites, direct and comprehensive analysis (metabolomics) must be considered an essential complement to genomic and proteomic approaches for establishing the structural repertoire within an organism and deducing its possible functional roles. The glycosphingolipidome clearly comprises an important and extensive subset of both the glycome and the lipidome, but the complexities of GSL structure, biosynthesis, and function form the outlines of a considerable analytical problem, especially since their structural diversity confers by extension an enormous variability with respect to physicochemical properties. This chapter covers selected developments and applications of techniques in mass spectrometric (MS) that have contributed to GSL structural analysis and glycosphingolipidomics since 1990. Sections are included on basic characteristics of ionization and fragmentation of permethylated GSLs and of lithium-adducted nonderivatized GSLs under positive-ion electrospray ionization mass spectrometry (ESI-MS) and collision-induced mass spectrometry (CID-MS) conditions; on the analysis of sulfatides, mainly using negative-ion techniques; and on selected applications of ESI-MS and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) to emerging GSL structural, functional, and analytical issues. The latter section includes a particular focus on evolving techniques for analysis of gangliosides, GSLs containing sialic acid, as well as on characterizations of GSLs from selected nonmammalian eukaryotes, such as dipterans, nematodes, cestodes, and fungi. Additional sections focus on the issue of whether it is better to leave GSLs intact or remove the ceramide; on development and uses of thin-layer chromatography (TLC) blotting and TLC-MS techniques; and on emerging issues of high-throughput analysis, including the use of flow injection, liquid chromatography mass spectrometry (LC-MS), and capillary electrophoresis mass spectrometry (CE-MS).

Isolation and partial characterization of Galalpha-containing polyglycosylceramides from porcine tissues

Mammalian cell surface carbohydrate antigens are present both as glycoproteins and glycolipids. Of the glycolipids, polyglycosylceramides (PGC) have very long carbohydrate chains extending out from the cell surface. Hereto, Gal alpha-terminating xenoantigens in pig tissues have been identified in glycoproteins and short chain glycolipids but no studies of the complex PGC have been performed. In this communication, we describe the isolation and partial characterization of PGC from pig erythrocytes, small intestinal mucosa, kidney and liver. The mucosa, kidney and liver PGC fractions contained a complex pattern of Gal alpha antigens as shown by immunostaining using the Griffonia Simplicifolia isolectin B(4) while no reactivity was found with the erythrocyte PGC fractions. The mucosa PGC fractions stained strongly for blood group A antigens while the erythrocyte PGC fractions were negative. The presence of Gal alpha-terminating PGC compounds in porcine tissue adds further complexity to the distribution of this xenoantigen. Due to the long carbohydrate chains, PGC will be important targets for the Gal alpha xenoantibodies in pig to human xenotransplantation.