Determination of glycolipid-protein interaction specificity

Probing the binding specificities of human Siglecs by cell-based glycan arrays

Siglecs are a family of sialic acid-binding receptors expressed by cells of the immune system and a few other cell types capable of modulating immune cell functions upon recognition of sialoglycan ligands. While human Siglecs primarily bind to sialic acid residues on diverse types of glycoproteins and glycolipids that constitute the sialome, their fine binding specificities for elaborated complex glycan structures and the contribution of the glycoconjugate and protein context for recognition of sialoglycans at the cell surface are not fully elucidated. Here, we generated a library of isogenic human HEK293 cells with combinatorial loss/gain of individual sialyltransferase genes and the introduction of sulfotransferases for display of the human sialome and to dissect Siglec interactions in the natural context of glycoconjugates at the cell surface. We found that Siglec-4/7/15 all have distinct binding preferences for sialylated GalNAc-type O-glycans but exhibit selectivity for patterns of O-glycans as presented on distinct protein sequences. We discovered that the sulfotransferase CHST1 drives sialoglycan binding of Siglec-3/8/7/15 and that sulfation can impact the preferences for binding to O-glycan patterns. In particular, the branched Neu5Acα2-3(6-O-sulfo)Galβ1-4GlcNAc (6'-Su-SLacNAc) epitope was discovered as the binding epitope for Siglec-3 (CD33) implicated in late-onset Alzheimer's disease. The cell-based display of the human sialome provides a versatile discovery platform that enables dissection of the genetic and biosynthetic basis for the Siglec glycan interactome and other sialic acid-binding proteins.

Sphingolipidomics in Translational Sepsis Research-Biomedical Considerations and Perspectives

Scientific Background: Sphingolipids are a highly diverse group of lipids with respect to physicochemical properties controlling either structure, distribution, or function, all of them regulating cellular response in health and disease. Mass spectrometry, on the other hand, is an analytical technique characterizing ionized molecules or fragments thereof by mass-to-charge ratios, which has been prosperingly developed for rapid and reliable qualitative and quantitative identification of lipid species. Parallel to best performance of in-depth chromatographical separation of lipid classes, preconditions of precise quantitation of unique molecular species by preprocessing of biological samples have to be fulfilled. As a consequence, “lipid profiles” across model systems and human individuals, esp. complex (clinical) samples, have become eminent over the last couple of years due to sensitivity, specificity, and discriminatory capability. Therefore, it is significance to consider the entire experimental strategy from sample collection and preparation, data acquisition, analysis, and interpretation.

Areas Covered: In this review, we outline considerations with clinical (i.e., human) samples with special emphasis on sample handling, specific physicochemical properties, target measurements, and resulting profiling of sphingolipids in biomedicine and translational research to maximize sensitivity and specificity as well as to provide robust and reproducible results. A brief commentary is also provided regarding new insights of “clinical sphingolipidomics” in translational sepsis research.

Expert Opinion: The role of mass spectrometry of sphingolipids and related species (“sphingolipidomics”) to investigate cellular and compartment-specific response to stress, e.g., in generalized infection and sepsis, is on the rise and the ability to integrate multiple datasets from diverse classes of biomolecules by mass spectrometry measurements and metabolomics will be crucial to fostering our understanding of human health as well as response to disease and treatment.

Don't sugarcoat it: How glycocalyx composition influences cancer progression

Buffone and Weaver discuss how the structure of the backbones and glycans of the tumor glycocalyx governs cell–matrix interactions and directs cancer progression.

Mechanical interactions between tumors and the extracellular matrix (ECM) of the surrounding tissues have profound effects on a wide variety of cellular functions. An underappreciated mediator of tumor–ECM interactions is the glycocalyx, the sugar-decorated proteins and lipids that act as a buffer between the tumor and the ECM, which in turn mediates all cell-tissue mechanics. Importantly, tumors have an increase in the density of the glycocalyx, which in turn increases the tension of the cell membrane, alters tissue mechanics, and drives a more cancerous phenotype. In this review, we describe the basic components of the glycocalyx and the glycan moieties implicated in cancer. Next, we examine the important role the glycocalyx plays in driving tension-mediated cancer cell signaling through a self-enforcing feedback loop that expands the glycocalyx and furthers cancer progression. Finally, we discuss current tools used to edit the composition of the glycocalyx and the future challenges in leveraging these tools into a novel tractable approach to treat cancer.

Host membrane glycosphingolipids and lipid microdomains facilitate Histoplasma capsulatum internalisation by macrophages

Recognition and internalisation of intracellular pathogens by host cells is a multifactorial process, involving both stable and transient interactions. The plasticity of the host cell plasma membrane is fundamental in this infectious process. Here, the participation of macrophage lipid microdomains during adhesion and internalisation of the fungal pathogen Histoplasma capsulatum (Hc) was investigated. An increase in membrane lateral organisation, which is a characteristic of lipid microdomains, was observed during the first steps of Hc-macrophage interaction. Cholesterol enrichment in macrophage membranes around Hc contact regions and reduced levels of Hc-macrophage association after cholesterol removal also suggested the participation of lipid microdomains during Hc-macrophage interaction. Using optical tweezers to study cell-to-cell interactions, we showed that cholesterol depletion increased the time required for Hc adhesion. Additionally, fungal internalisation was significantly reduced under these conditions. Moreover, macrophages treated with the ceramide-glucosyltransferase inhibitor (P4r) and macrophages with altered ganglioside synthesis (from B4galnt1^-/- mice) showed a deficient ability to interact with Hc. Coincubation of oligo-GM1 and treatment with Cholera toxin Subunit B, which recognises the ganglioside GM1, also reduced Hc association. Although purified GM1 did not alter Hc binding, treatment with P4 significantly increased the time required for Hc binding to macrophages. The content of CD18 was displaced from lipid microdomains in B4galnt1^-/- macrophages. In addition, macrophages with reduced CD18 expression (CD18^low ) were associated with Hc at levels similar to wild-type cells. Finally, CD11b and CD18 colocalised with GM1 during Hc-macrophage interaction. Our results indicate that lipid rafts and particularly complex gangliosides that reside in lipid rafts stabilise Hc-macrophage adhesion and mediate efficient internalisation during histoplasmosis.

Siglec-8 and Siglec-9 binding specificities and endogenous airway ligand distributions and properties

Siglecs are transmembrane sialoglycan binding proteins, most of which are expressed on leukocyte subsets and have inhibitory motifs that translate cell surface ligation into immune suppression. In humans, Siglec-8 on eosinophils, mast cells and basophils and Siglec-9 on neutrophils, monocytes and some T-cells, mediate immune cell death, inhibition of immune mediator release and/or enhancement of anti-inflammatory mediator release. Endogenous sialoglycan ligands in tissues, mostly uncharacterized, engage siglecs on leukocytes to inhibit inflammation. Glycan array analyses demonstrated that Siglec-8, Siglec-9 and their mouse counterparts Siglec-F and Siglec-E (respectively) have distinct glycan binding specificities, with Siglec-8 more structurally restricted. Since siglecs are involved in lung inflammation, we studied Siglec-8 and Siglec-9 ligands in human lungs and airways. Siglec-8 ligands are in tracheal submucosal glands and cartilage but not airway epithelium or connective tissues, whereas Siglec-9 ligands are broadly distributed. Mouse airways do not have Siglec-8 ligands, whereas Siglec-9 ligands are on airways of both species. Extraction of human airways and lung followed by electrophoretic resolution and siglec blotting revealed Siglec-8 ligands in extracts of human trachea and cultured tracheal gland cells, but not parenchyma or cultured airway epithelial cells whereas Siglec-9 ligands were extracted from all airway and lung tissues and cells tested. Siglec-8 and Siglec-9 ligands in airways appear to be high molecular weight O-linked sialoglycoproteins. These data reveal differential glycan specificities of Siglec-8, Siglec-9 and their mouse counterparts Siglec-F and Siglec-E, and the tissue distributions and molecular characteristics of Siglec-8 and Siglec-9 sialoglycan ligands on human airways and lungs.

Microfluidics-Mass Spectrometry of Protein-Carbohydrate Interactions: Applications to the Development of Therapeutics and Biomarker Discovery

The functional interactions of carbohydrates and their protein receptors are the basis of biological events critical to the evolution of pathological states. Hence, for the past years, such interactions have become the focus of research for the development of therapeutics and discovery of novel glycan biomarkers based on their binding affinity. Due to the high sensitivity, throughput, reproducibility, and capability to ionize minor species in heterogeneous mixtures, microfluidics-mass spectrometry (MS) has recently emerged as a method of choice in protein-glycan interactomics. In this chapter, a straightforward microfluidics-based MS methodology for the assessment of protein-glycan interactions is presented. The general protocol encompasses: (1) submission of the interacting partners to a binding assay under conditions mimicking the in vivo environment; and (2) screening of the reaction products and their structural characterization by fully automated chip-nanoelectrospray (nanoESI) MS and multistage MS. The first section of the chapter is devoted to describing a method that enables the study of protein-oligosaccharide interactions by chip-nanoESI quadrupole time-of-flight (QTOF) MS and top-down complex analysis by collision-induced dissociation (CID). This section provides the protocol for the determination of the complex formed by standard β-lactoglobulin (BLG) with maltohexaose (Glc₆) and recommends as a concrete application the study of the interaction between BLG extracted from human milk with Glc₆, considered a ligand able to reduce the allergenicity of this protein. The second part is dedicated to presenting the protocols for the binding assay followed by chip-nanoESI ion trap (ITMS) and electron transfer dissociation (ETD) in combination with CID for protein-ganglioside interactions, using as an example the B subunit of cholera toxin (Ctb5) in interaction with comercially available GM1 species. The methodology described may be successfully applied to native ganglioside mixtures from human brain, in particular for discovery of biomarkers on the basis of their binding affinity.

Detecting Protein-Glycolipid Interactions Using Glycomicelles and CaR-ESI-MS

This study reports on the use of the catch-and-release electrospray ionization mass spectrometry (CaR-ESI-MS) assay, combined with glycomicelles, as a method for detecting specific interactions between water-soluble proteins and glycolipids (GLs) in aqueous solution. The B subunit homopentamers of cholera toxin (CTB₅) and Shiga toxin type 1 B (Stx1B₅) and the gangliosides GM1, GM2, GM3, GD1a, GD1b, GT1b, and GD2 served as model systems for this study. The CTB₅ exhibits broad specificity for gangliosides and binds to GM1, GM2, GM3, GD1a, GD1b, and GT1b; Stx1B₅ does not recognize gangliosides. The CaR-ESI-MS assay was used to analyze solutions of CTB₅ or Stx1B₅ and individual gangliosides (GM1, GM2, GM3, GD1a, GD1b, GT1b, and GD2) or mixtures thereof. The high affinity interaction of CTB₅ with GM1 was successfully detected. However, the apparent affinity, as determined from the mass spectra, is significantly lower than that of the corresponding pentasaccharide or when GM1 is presented in model membranes such as nanodiscs. Interactions between CTB₅ and the low affinity gangliosides GD1a, GD1b, and GT1b, as well as GD2, which served as a negative control, were detected; no binding of CTB₅ to GM2 or GM3 was observed. The CaR-ESI-MS results obtained for Stx1B₅ reveal that nonspecific protein-ganglioside binding can occur during the ESI process, although the extent of binding varies between gangliosides. Consequently, interactions detected for CTB₅ with GD1a, GD1b, and GT1b are likely nonspecific in origin. Taken together, these results reveal that the CaR-ESI-MS/glycomicelle approach for detecting protein-GL interactions is prone to false positives and false negatives and must be used with caution. Graphical Abstract <!-- [INSERT GRAPHICAL ABSTRACT TEXT HERE] -->.

Mice lacking sialyltransferase ST3Gal-II develop late-onset obesity and insulin resistance

Sialyltransferases are a family of 20 gene products in mice and humans that transfer sialic acid from its activated precursor, CMP-sialic acid, to the terminus of glycoprotein and glycolipid acceptors. ST3Gal-II (coded by the St3gal2 gene) transfers sialic acid preferentially to the three positions of galactose on the Galβ1-3GalNAc terminus of gangliosides GM1 and GD1b to synthesize GD1a and GT1b, respectively. Mice with a targeted disruption of St3gal2 unexpectedly displayed late-onset obesity and insulin resistance. At 3 months of age, St3gal2-null mice were the same weight as their wild type (WT) counterparts, but by 13 months on standard chow they were visibly obese, 22% heavier and with 37% greater fat/lean ratio than WT mice. St3gal2-null mice became hyperglycemic and displayed impaired glucose tolerance by 9 months of age. They had sharply reduced insulin responsiveness despite equivalent pancreatic islet morphology. Analyses of insulin receptor (IR) tyrosine kinase substrate IRS-1 and downstream target Akt revealed decreased insulin-induced phosphorylation in adipose tissue but not liver or skeletal muscle of St3gal2-null mice. Thin-layer chromatography and mass spectrometry revealed altered ganglioside profiles in the adipose tissue of St3gal2-null mice compared to WT littermates. Metabolically, St3gal2-null mice display a reduced respiratory exchange ratio compared to WT mice, indicating a preference for lipid oxidation as an energy source. Despite their altered metabolism, St3gal2-null mice were hyperactive. We conclude that altered ganglioside expression in adipose tissue results in diminished IR sensitivity and late-onset obesity.

Characterizing the Size and Composition of Saposin A Lipoprotein Picodiscs

Saposin A (SapA) lipoprotein discs, also known as picodiscs (PDs), represent an attractive method to solubilize glycolipids for protein interaction studies in aqueous solution. Recent electrospray ionization mass spectrometry (ESI-MS) data suggest that the size and composition of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)-containing PDs at neutral pH differs from those of N,N-dimethyldodecylamine N-oxide determined by X-ray crystallography. Using high-resolution ESI-MS, multiangle laser light scattering (MALLS), and molecular dynamics (MD) simulations, the composition, heterogeneity, and structure of POPC-PDs in aqueous ammonium acetate solutions at pH 4.8 and 6.8 were investigated. The ESI-MS and MALLS data revealed that POPC-PDs consist predominantly of (SapA dimer + iPOPC) complexes, with i = 23-29, and have an average molecular weight (MW) of 38.2 ± 3.3 kDa at pH 4.8. In contrast, in freshly prepared solutions at pH 6.8, POPC-PDs are composed predominantly of (SapA tetramer + iPOPC) complexes, with i = 37-60, with an average MW of 68.0 ± 2.7 kDa. However, the (SapA tetramer + iPOPC) complexes are unstable at neutral pH and convert, over a period of hours, to (SapA trimer + iPOPC) complexes, with i = 29-36, with an average MW of 51.1 ± 2.9 kDa. The results of molecular modeling suggest spheroidal structures for the (SapA dimer + iPOPC), (SapA trimer + iPOPC), and (SapA tetramer + iPOPC) complexes in solution. Comparison of measured collision cross sections (Ω) with values calculated for gaseous (SapA dimer + 26POPC)⁸⁺, (SapA trimer + 33POPC)¹²⁺, and (SapA tetramer + 42POPC)¹⁶⁺ ions produced from modeling suggests that the solution structures are largely preserved in the gas phase, although the lipids do not maintain regular bilayer orientations.

Screening Glycolipids Against Proteins in Vitro Using Picodiscs and Catch-and-Release Electrospray Ionization-Mass Spectrometry

This work describes the application of the catch-and-release electrospray ionization-mass spectrometry (CaR-ESI-MS) assay, implemented using picodiscs (complexes comprised of saposin A and lipids, PDs), to screen mixtures of glycolipids (GLs) against water-soluble proteins to detect specific interactions. To demonstrate the reliability of the method, seven gangliosides (GM1, GM2, GM3, GD1a, GD1b, GD2, and GT1b) were incorporated, either individually or as a mixture, into PDs and screened against two lectins: the B subunit homopentamer of cholera toxin (CTB5) and a subfragment of toxin A from Clostridium difficile (TcdA-A2). The CaR-ESI-MS results revealed that CTB5 binds to six of the gangliosides (GM1, GM2, GM3, GD1a, GD1b, and GT1b), while TcdA-A2 binds to five of them (GM1, GM2, GM3, GD1a, and GT1b). These findings are consistent with the measured binding specificities of these proteins for ganglioside oligosaccharides. Screening mixtures of lipids extracted from porcine brain and a human epithelial cell line against CTB5 revealed binding to multiple GM1 isoforms as well as to fucosyl-GM1, which is a known ligand. Finally, a comparison of the present results with data obtained with the CaR-ESI-MS assay implemented using nanodiscs (NDs) revealed that the PDs exhibited similar or superior performance to NDs for protein-GL binding measurements.

Myelin-associated glycoprotein modulates apoptosis of motoneurons during early postnatal development via NgR/p75(NTR) receptor-mediated activation of RhoA signaling pathways

Myelin-associated glycoprotein (MAG) is a minor constituent of nervous system myelin, selectively expressed on the periaxonal myelin wrap. By engaging multiple axonal receptors, including Nogo-receptors (NgRs), MAG exerts a nurturing and protective effect the axons it ensheaths. Pharmacological activation of NgRs has a modulatory role on p75^NTR-dependent postnatal apoptosis of motoneurons (MNs). However, it is not clear whether this reflects a physiological role of NgRs in MN development. NgRs are part of a multimeric receptor complex, which includes p75^NTR, Lingo-1 and gangliosides. Upon ligand binding, this multimeric complex activates RhoA/ROCK signaling in a p75^NTR-dependent manner. The aim of this study was to analyze a possible modulatory role of MAG on MN apoptosis during postnatal development. A time course study showed that Mag-null mice suffer a loss of MNs during the first postnatal week. Also, these mice exhibited increased susceptibility in an animal model of p75^NTR-dependent MN apoptosis induced by nerve-crush injury, which was prevented by treatment with a soluble form of MAG (MAG-Fc). The protective role of MAG was confirmed in in vitro models of p75^NTR-dependent MN apoptosis using the MN1 cell line and primary cultures. Lentiviral expression of shRNA sequences targeting NgRs on these cells abolished protection by MAG-Fc. Analysis of RhoA activity using a FRET-based RhoA biosensor showed that MAG-Fc activates RhoA. Pharmacological inhibition of p75^NTR/RhoA/ROCK pathway, or overexpression of a p75^NTR mutant unable to activate RhoA, completely blocked MAG-Fc protection against apoptosis. The role of RhoA/ROCK signaling was further confirmed in the nerve-crush model, where pretreatment with ROCK inhibitor Y-27632 blocked the pro-survival effect of MAG-Fc. These findings identify a new protective role of MAG as a modulator of apoptosis of MNs during postnatal development by a mechanism involving the p75^NTR/RhoA/ROCK signaling pathway. Also, our results highlight the relevance of the nurture/protective effects of myelin on neurons.

Picodiscs for facile protein-glycolipid interaction analysis

Protein interactions with glycolipids are implicated in diverse cellular processes. However, the study of protein-glycolipid complexes remains a significant experimental challenge. Here, we describe a powerful new assay that combines electrospray ionization mass spectrometry (ESI-MS) and picodiscs, which are composed of human sphingolipid activator protein saposin A and a small number of phospholipids, to display glycolipids in a lipid environment for protein-glycolipid interaction studies in aqueous solution. Time-resolved measurements of enzyme catalyzed hydrolysis of glycolipid substrates and the detection of low, moderate, and high affinity protein-glycolipid interactions serve to demonstrate the reliability and versatility of the assay.

Anti-streptococcal, tubulin, and dopamine receptor 2 antibodies in children with PANDAS and Tourette syndrome: single-point and longitudinal assessments

Single-point-in-time ELISA optical densities for three putative antibodies identified in Sydenham's chorea, the streptococcal group A carbohydrate antigen, N-acetyl-beta-d-glucosamine, tubulin, and the dopamine 2 receptor, showed no differences in children with PANDAS (n=44) or Tourette syndrome (n=40) as compared to controls (n=24). Anti-tubulin and D2 receptor antibodies assessed in serial samples from 12 PANDAS subjects obtained prior to a documented exacerbation, during the exacerbation (with or without a temporally associated streptococcal infection), and following the exacerbation, showed no evidence of antibody levels correlating with a clinical exacerbation. These data do not support hypotheses suggesting an autoimmune hypothesis in either TS or PANDAS.

Lipidomics of glycosphingolipids

Glycosphingolipids (GSLs) contain one or more sugars that are attached to a sphingolipid moiety, usually to a ceramide, but in rare cases also to a sphingoid base. A large structural heterogeneity results from differences in number, identity, linkage, and anomeric configuration of the carbohydrate residues, and also from structural differences within the hydrophobic part. GSLs form complex cell-type specific patterns, which change with the species, the cellular differentiation state, viral transformation, ontogenesis, and oncogenesis. Although GSL structures can be assigned to only a few series with a common carbohydrate core, their structural variety and the complex pattern are challenges for their elucidation and quantification by mass spectrometric techniques. We present a general overview of the application of lipidomics for GSL determination. This includes analytical procedures and instrumentation together with recent correlations of GSL molecular species with human diseases. Difficulties such as the structural complexity and the lack of standard substances for complex GSLs are discussed.

Natural glycan microarrays

Glycan microarrays are emerging as increasingly used screening tools with a high potential for unraveling protein-carbohydrate interactions: probing hundreds or even thousands of glycans in parallel, they provide the researcher with a vast amount of data in a short time-frame, while using relatively small amounts of analytes. Natural glycan microarrays focus on the glycans' repertoire of natural sources, including both well-defined structures as well as still-unknown ones. This article compares different natural glycan microarray strategies. Glycan probes may comprise oligosaccharides from glycoproteins as well as glycolipids and polysaccharides. Oligosaccharides may be purified from scarce biological samples that are of particular relevance for the carbohydrate-binding protein to be studied. We give an overview of strategies for glycan isolation, derivatization, fractionation, immobilization and structural characterization. Detection methods such as fluorescence analysis and surface plasmon resonance are summarized. The importance of glycan density and multivalency is discussed. Furthermore, some applications of natural glycan microarrays for studying lectin and antibody binding are presented.

Shotgun glycomics: a microarray strategy for functional glycomics

Major challenges of glycomics are to characterize a glycome and identify functional glycans as ligands for glycan-binding proteins (GBPs). To address these issues we have developed a general strategy termed shotgun glycomics. We focus on glycosphingolipids (GSLs), a challenging class of glycoconjugates recognized by toxins, antibodies, and GBPs. We derivatized GSLs extracted from cells with a heterobifunctional fluorescent tag suitable for covalent immobilization. Fluorescent GSLs were separated by multidimensional chromatography, quantified, and coupled to glass slides to create GSL shotgun microarrays. The microarrays were interrogated with cholera toxin, antibodies, and sera from patients with Lyme disease to identify biologically relevant GSLs that were subsequently characterized by mass spectrometry. Shotgun glycomics incorporating GSLs and potentially glycoprotein-derived glycans provides an approach to accessing the complex glycomes of animal cells and offers a strategy for focusing structural analyses on functionally significant glycans.

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.

Lectins as tools in glycoconjugate research

Lectins are ubiquitous proteins of nonimmune origin, present in plants, microorganisms, animals and humans which specifically bind defined monosugars or oligosaccharide structures. Great progress has been made in recent years in understanding crucial roles played by lectins in many biological processes. Elucidation of carbohydrate specificity of human and animal lectins is of great importance for better understanding of these processes. Long before the role of carbohydrate-protein interactions had been explored, many lectins, mostly of plant origin, were identified, characterized and applied as useful tools in studying glycoconjugates. This review focuses on the specificity-based lectin classification and the methods of measuring lectin-carbohydrate interactions, which are used for determination of lectin specificity or for identification and characterization of glycoconjugates with lectins of known specificity. The most frequently used quantitative methods are shortly reviewed and the methods elaborated and used in our laboratories, based on biotinylated lectins, are described. These include the microtiter plate enzyme-linked lectinosorbent assay, lectinoblotting and lectin-glycosphingolipid interaction on thin-layer plates. Some chemical modifications of lectin ligands on the microtiter plates and blots (desialylation, Smith degradation, beta-elimination), which extend the applicability of these methods, are also described.

Incorporation of a transmembrane protein into a supported 3D-matrix of liposomes for SPR studies

Surface analytical tools as surface plasmon resonance (SPR) have become increasingly important in biomedical research since they offer high detection sensitivity compared to traditional biomedical methods. For the use of SPR as a biomedical research tool there is a need to immobilize the reactants to a solid sensor surface. It is nowadays fairly straightforward to immobilize various reactants and hydrophilic proteins to a solid sensor surface and SPR has successfully been used in several applications using such proteins when studying various protein interactions. When using SPR for the analysis of transmembrane proteins the immobilization onto the solid surface becomes more difficult. Transmembrane proteins are more sensitive to the surroundings and need to be incorporated into a structure where it can reside in a natural environment. Supported liposomes offer such environment. In this chapter a new method is presented where multilayers of such supported liposomes are used to immobilize transmembrane proteins onto a solid sensor surface which is suitable for use in SPR detection.

Fluorescent glycosylamides produced by microscale derivatization of free glycans for natural glycan microarrays

A novel strategy for creating naturally derived glycan microarrays has been developed. Glycosylamines are prepared from free reducing glycans and stabilized by reaction with acryloyl chloride to generate a glycosylamide in which the reducing monosaccharide has a closed-ring structure. Ozonolysis of the protected glycan yields an active aldehyde, to which a bifunctional fluorescent linker is coupled by reductive amination. The fluorescent derivatives are easily coupled through a residual primary alkylamine to generate glycan microarrays. This strategy preserves structural features of glycans required for antibody recognition and allows development of natural arrays of fluorescent glycans in which the cyclic pyranose structure of the reducing-end sugar residue is retained.

Generation of a natural glycan microarray using 9-fluorenylmethyl chloroformate (FmocCl) as a cleavable fluorescent tag

Glycan microarray technology has become a successful tool for studying protein-carbohydrate interactions, but a limitation has been the laborious synthesis of glycan structures by enzymatic and chemical methods. Here we describe a new method to generate quantifiable glycan libraries from natural sources by combining widely used protease digestion of glycoproteins and Fmoc chemistry. Glycoproteins including chicken ovalbumin, bovine fetuin, and horseradish peroxidase (HRP) were digested by Pronase, protected by FmocCl, and efficiently separated by 2D-HPLC. We show that glycans from HRP glycopeptides separated by HPLC and fluorescence monitoring retained their natural reducing end structures, mostly core alpha1,3-fucose and core alpha1,2-xylose. After simple Fmoc deprotection, the glycans were printed on NHS-activated glass slides. The glycans were interrogated using plant lectins and antibodies in sera from mice infected with Schistosoma mansoni, which revealed the presence of both IgM and IgG antibody responses to HRP glycopeptides. This simple approach to glycopeptide purification and conjugation allows for the development of natural glycopeptide microarrays without the need to remove and derivatize glycans and potentially compromise their reducing end determinants.

Serial immune markers do not correlate with clinical exacerbations in pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections

OBJECTIVE

Pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections is hypothesized to be a poststreptococcal autoimmune disorder. If clinical exacerbations are triggered by a streptococcal infection that activates cross-reacting antibodies against neuronal tissue or alters the production of cytokines, then a longitudinal analysis would be expected to identify a correlation between clinical symptoms and a change in autoimmune markers.

PATIENTS AND METHODS

Serial serum samples were available on 12 children with pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections participating in a prospective blinded study: 2 samples before an exacerbation point, 1 during the clinical exacerbation, and 2 after the exacerbation. Six subjects had a well-defined clinical exacerbation in association with a documented streptococcal infection, and 6 had a clinical exacerbation without an associated streptococcal infection. All of the serum samples were assayed for antibodies against human postmortem caudate, putamen, and prefrontal cortex; commercially prepared antigens; and complex sugars. Cytokines were measured by 2 different methodologies.

RESULTS

No correlation was identified between clinical exacerbations and autoimmune markers, including: enzyme-linked immunosorbent assay measures of antineuronal antibodies; Western immunoblotting with emphasis on brain region proteins located at 40, 45, and 60 kDa or their corresponding identified antigens; competitive inhibition enzyme-linked immunosorbent assay to evaluate lysoganglioside G(M1) antibodies; and measures of inflammatory cytokines. No differences were identified between individuals with pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections with or without exacerbations triggered by streptococcal infections.

CONCLUSIONS

The failure of immune markers to correlate with clinical exacerbations in children with pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections raises serious concerns about the viability of autoimmunity as a pathophysiological mechanism in this disorder.