Structural characterization by multistage mass spectrometry (MSn) of human milk glycans recognized by human rotaviruses

Isolation of Human Milk Difucosyl Nona- and Decasaccharides by Ultrahigh-Temperature Preparative PGC-HPLC and Identification of Novel Difucosylated Heptaose and Octaose Backbones by Negative-Ion ESI-MSn

Despite their many important physiological functions, past work on the diverse sequences of human milk oligosaccharides (HMOs) has been focused mainly on the highly abundant HMOs with a relatively low degree of polymerization (DP) due to the lack of efficient methods for separation/purification and high-sensitivity sequencing of large-sized HMOs with DP ≥ 10. Here we established an ultrahigh-temperature preparative HPLC based on a porous graphitized carbon column at up to 145 °C to overcome the anomeric α/β splitting problem and developed further the negative-ion ESI-CID-MS/MS into multistage MSn using a combined product-ion scanning of singly charged molecular ion and doubly charged fragment ion of the branching Gal and adjacent GlcNAc residues. The separation and sequencing method allows efficient separation of a neutral fraction with DP ≥ 10 into 70 components, among which 17 isomeric difucosylated nona- and decasaccharides were further purified and sequenced. As a result, novel branched difucosyl heptaose and octaose backbones were unambiguously identified in addition to the conventional linear and branched octaose backbones. The novel structures of difucosylated DF-novo-heptaose, DF-novo-LNO I, and DF-novo-LNnO I were corroborated by NMR. The various fucose-containing Lewis epitopes identified on different backbones were confirmed by oligosaccharide microarray analysis.

Chemical Synthesis of Human Milk Oligosaccharides: para-Lacto-N-hexaose and para-Lacto-N-neohexaose

Human milk oligosaccharides (HMO) have emerged as a very active area of research in glycoscience and nutrition. HMO are involved in the early development of infants and may help to prevent certain diseases. The development of chemical methods for obtaining individual HMO aids the global effort dedicated to understanding the roles of these biomolecules. Reported herein is the chemical synthesis of two common core hexasaccharides found in human milk, i. e. para-lacto-N-hexaose (pLNH) and para-lacto-N-neohexaose (pLNnH). After screening multiple leaving groups and temporary protecting group combinations, a 3+3 convergent coupling strategy was found to work best for obtaining these linear glycans.

Comparison of liquid chromatography-high-resolution tandem mass spectrometry (MS2) and multi-stage mass spectrometry (MS3) for screening toxic natural products

Background

Liquid chromatography-high-resolution mass spectrometry (LC-HR-MS) has emerged as a powerful analytical technology for compound screening in clinical toxicology. To evaluate the potential of LC-HR-MS3 in detecting toxic natural products, a spectral library of 85 natural products (79 alkaloids) that contains both MS2 and MS3 mass spectra was constructed and used to identify the natural products. Samples were analyzed using an LC-HR-MS3 method and the generated data were matched to the spectral library to identify the natural products.

Methods

To test the performance of the LC-HR-MS3 method in different sample matrices, the 85 natural product standards were divided into three groups to separate structural isomers and avoid ion suppression effects caused by co-elution of multiple analytes. The grouped analytes were spiked into drug-free serum and drug-free urine to produce contrived clinical samples.

Results

The compound identification results of the 85 natural products in urine and serum samples were obtained. The match scores using both MS2 and MS3 mass spectra and those using only MS2 mass spectra were compared at 10 different analyte concentrations. The two types of data analysis provided identical identification results for the majority of the analytes (96% in serum, 92% in urine), whereas, for the remaining analytes, the MS2-MS3 tree data analysis had better performance in identifying them at lower concentrations.

Conclusion

This study shows that in comparison to LC-HR-MS (MS2), LC-HR-MS3 can increase the performance in identification of a small group of the toxic natural products tested in serum and urine specimens.

Comprehensive investigation of milk oligosaccharides in different mammalian species and the effect of breed and lactation period on sheep milk oligosaccharides

Milk oligosaccharides (MOs) have unique health benefits for newborns, and MOs are important components in mammalian milk. The present study was conducted to provide a comprehensive analysis of MOs in important domestic animals, including goats, cows, camels and sheep. The comparison with human MOs was conducted simultaneously. Furthermore, analysis of the relative abundance of sheep MOs among different breeds (Hu sheep, East Friesen sheep, East Friesen-Hu crossbred sheep) and lactation periods (colostrum, mature milk) was performed. In general, 35, 24 19, 26, and 16 MOs were identified in human, goat, bovine, camel and sheep milk, respectively. The type of sheep MOs was not greatly influenced by the breeds and lactation period. Hu sheep colostrum had the highest abundance of MOs among six sheep milks, followed by East Friesen sheep colostrum, while East Friesen-Hu crossbred sheep mature milk had the lowest abundance of MOs. These findings provide evidence for the potential value of MOs from domestic animal milk for the commercial applications.

De novo glycan sequencing by electronic excitation dissociation MS2-guided MS3 analysis on an Omnitrap-Orbitrap hybrid instrument

Comprehensive de novo glycan sequencing remains an elusive goal due to the structural diversity and complexity of glycans. Present strategies employing collision-induced dissociation (CID) and higher energy collisional dissociation (HCD)-based multi-stage tandem mass spectrometry (MSⁿ) or MS/MS combined with sequential exoglycosidase digestions are inherently low-throughput and difficult to automate. Compared to CID and HCD, electron transfer dissociation (ETD) and electron capture dissociation (ECD) each generate more cross-ring cleavages informative about linkage positions, but electronic excitation dissociation (EED) exceeds the information content of all other methods and is also applicable to analysis of singly charged precursors. Although EED can provide extensive glycan structural information in a single stage of MS/MS, its performance has largely been limited to FTICR MS, and thus it has not been widely adopted by the glycoscience research community. Here, the effective performance of EED MS/MS was demonstrated on a hybrid Orbitrap-Omnitrap QE-HF instrument, with high sensitivity, fragmentation efficiency, and analysis speed. In addition, a novel EED MS²-guided MS³ approach was developed for detailed glycan structural analysis. Automated topology reconstruction from MS² and MS³ spectra could be achieved with a modified GlycoDeNovo software. We showed that the topology and linkage configurations of the Man₉GlcNAc₂ glycan can be accurately determined from first principles based on one EED MS² and two CID-EED MS³ analyses, without reliance on biological knowledge, a structure database or a spectral library. The presented approach holds great promise for autonomous, comprehensive and de novo glycan sequencing.

Human Milk Oligosaccharide Profile across Lactation Stages in Israeli Women-A Prospective Observational Study

Human milk oligosaccharides (HMOs) stimulate the growth of gut commensals, prevent the adhesion of enteropathogens and modulate host immunity. The major factors influencing variations in the HMO profile are polymorphisms in the secretor (Se) or Lewis (Le) gene, which affect the activity of the enzymes fucoslytransferase 2 and 3 (FUT2 and FUT3) that lead to the formation of four major fucosylated and non-fucosylated oligosaccharides (OS). This pilot study aimed to determine the HMO profile of Israeli breastfeeding mothers of 16 term and 4 preterm infants, from a single tertiary center in the Tel Aviv area. Fifty-two human milk samples were collected from 20 mothers at three-time points: colostrum, transitional milk and mature milk. The concentrations of nine HMOs were assessed using liquid chromatography coupled with mass spectra chromatograms. Fifty-five percent of the mothers were secretors and 45% were non-secretors. Infant sex affected HMO levels depending on the maternal secretor status. Secretor mothers to boys had higher levels of FUT2-dependent OS and higher levels of disialyllacto-N-tetraose in the milk of mothers to girls, whereas non-secretor mothers to girls had higher levels of 3'-sialyllactose. In addition, the season at which the human milk samples were obtained affected the levels of some HMOs, resulting in significantly lower levels in the summer. Our findings provide novel information on the irregularity in the HMO profile among Israeli lactating women and identify several factors contributing to this variability.

Determinants of human milk oligosaccharides profiles of participants in the STRONG kids 2 cohort

Introduction

Human milk oligosaccharides (HMOS) are indigestible carbohydrates that support infant development by establishing a healthy microbiota, preventing infectious diseases, and promoting immune and cognitive development. Individual HMOS have distinct functions based on their chemical structures. HMO profiles can vary largely among mothers, but the research on factors other than genetic background affecting HMO composition are limited.

Methods

In the present analysis, we examined the relationships between maternal characteristics and the HMO profiles of breastfeeding mothers (n = 392) in the STRONG kids 2 with the following demographic characteristics: average age: 30.8 y, 74.5% White, and 75.5% exclusively breastfeeding. Human milk samples were collected at 6 weeks postpartum and maternal information was obtained from self-reported surveys. Information on dietary intake changes since the participants have been breastfeeding was collected. HMO profiles were analyzed by high performance liquid chromatography coupled with mass spectrometry and secretor status was determined by the presence of four secretor markers [2′-fucosyllactose (2′-FL), LNFP I, LDFT, and TFLNH]. Spearmen correlation test was utilized to determine the relationships between individual HMOS and associations with maternal factors. Between-group differences in HMO relative abundances were examined with Kruskal-Wallis test.

Results

Among all participants, 71.9% were secretors and 28.1% were non-secretors. The relative abundances of all HMOS differed (p < 0.05) by secretor status, with the exception for 6′-SL and 3′-SL. Positive correlations were observed among HMOS with similar structures, such as the 1,2-fucosylated HMOS. The abundances of selected HMOS were associated with maternal body weight, pregnancy complications, and dietary characteristics. Based on pre-pregnancy BMI, in all mothers, relative abundance of 3′-SL was significantly higher in overweight mothers than obese mothers (p = 0.013). In milk produced by non-secretor mothers, LNPF I + III abundances were greater in overweight than normal weight mothers (p = 0.020). Several HMO abundances were found to be associated with Gestational diabetes mellitus (GDM). Variations of HMO abundances were also observed with dietary food intake. In all mothers, egg consumption was positively correlated with LNT + LNnT (R = 0.13; p = 0.012) and cheese intake was positively associated with 2′-FL (R = 0.10; p = 0.046) and S-LNnH II (R = 0.11; p = 0.026) abundances.

Discussion

HMO profiles were found to be associated with maternal characteristics and intake. Future research will investigate associations between HMOS and maternal and infant outcomes.

MS-based glycomics and glycoproteomics methods enabling isomeric characterization

Glycosylation is one of the most significant and abundant posttranslational modifications in mammalian cells. It mediates a wide range of biofunctions, including cell adhesion, cell communication, immune cell trafficking, and protein stability. Also, aberrant glycosylation has been associated with various diseases such as diabetes, Alzheimer's disease, inflammation, immune deficiencies, congenital disorders, and cancers. The alterations in the distributions of glycan and glycopeptide isomers are involved in the development and progression of several human diseases. However, the microheterogeneity of glycosylation brings a great challenge to glycomic and glycoproteomic analysis, including the characterization of isomers. Over several decades, different methods and approaches have been developed to facilitate the characterization of glycan and glycopeptide isomers. Mass spectrometry (MS) has been a powerful tool utilized for glycomic and glycoproteomic isomeric analysis due to its high sensitivity and rich structural information using different fragmentation techniques. However, a comprehensive characterization of glycan and glycopeptide isomers remains a challenge when utilizing MS alone. Therefore, various separation methods, including liquid chromatography, capillary electrophoresis, and ion mobility, were developed to resolve glycan and glycopeptide isomers before MS. These separation techniques were coupled to MS for a better identification and quantitation of glycan and glycopeptide isomers. Additionally, bioinformatic tools are essential for the automated processing of glycan and glycopeptide isomeric data to facilitate isomeric studies in biological cohorts. Here in this review, we discuss commonly employed MS-based techniques, separation hyphenated MS methods, and software, facilitating the separation, identification, and quantitation of glycan and glycopeptide isomers.

GIPS-Mix for Accurate Identification of Isomeric Components in Glycan Mixtures Using Intelligent Group-Opting Strategy

Accurate identification of glycan structures is highly desirable as they are intimately linked to their different functions. However, glycan samples generally exist as mixtures with multiple isomeric structures, making assignment of individual glycan components very challenging, even with the aid of multistage mass spectrometry (MSⁿ). Here, we present an approach, GIPS-mix, for assignment of isomeric glycans within a mixture using an intelligent group-opting strategy. Our approach enumerates all possible combinations (groupings) of candidate glycans and opts in the best-matched glycan group(s) based on the similarity between the simulated spectra of each glycan group and the acquired experimental spectra of the mixture. In the case that a single group could not be elected, a tie break is performed by additional MSⁿ scanning using intelligently selected precursors. With 11 standard mixtures and 6 human milk oligosaccharide fractions, we demonstrate the application of GIPS-mix in assignment of individual glycans in mixtures with high accuracy and efficiency.

MS-based glycomics: An analytical tool to assess nervous system diseases

Neurological diseases affect millions of peopleochemistryorldwide and are continuously increasing due to the globe's aging population. Such diseases affect the nervous system and are characterized by a progressive decline in brain function and progressive cognitive impairment, decreasing the quality of life for those with the disease as well as for their families and loved ones. The increased burden of nervous system diseases demands a deeper insight into the biomolecular mechanisms at work during disease development in order to improve clinical diagnosis and drug design. Recently, evidence has related glycosylation to nervous system diseases. Glycosylation is a vital post-translational modification that mediates many biological functions, and aberrant glycosylation has been associated with a variety of diseases. Thus, the investigation of glycosylation in neurological diseases could provide novel biomarkers and information for disease pathology. During the last decades, many techniques have been developed for facilitation of reliable and efficient glycomic analysis. Among these, mass spectrometry (MS) is considered the most powerful tool for glycan analysis due to its high resolution, high sensitivity, and the ability to acquire adequate structural information for glycan identification. Along with MS, a variety of approaches and strategies are employed to enhance the MS-based identification and quantitation of glycans in neurological samples. Here, we review the advanced glycomic tools used in nervous system disease studies, including separation techniques prior to MS, fragmentation techniques in MS, and corresponding strategies. The glycan markers in common clinical nervous system diseases discovered by utilizing such MS-based glycomic tools are also summarized and discussed.

In silico analysis of the human milk oligosaccharide glycome reveals key enzymes of their biosynthesis

Human milk oligosaccharides (HMOs) form the third most abundant component of human milk and are known to convey several benefits to the neonate, including protection from viral and bacterial pathogens, training of the immune system, and influencing the gut microbiome. As HMO production during lactation is driven by enzymes that are common to other glycosylation processes, we adapted a model of mucin-type GalNAc-linked glycosylation enzymes to act on free lactose. We identified a subset of 11 enzyme activities that can account for 206 of 226 distinct HMOs isolated from human milk and constructed a biosynthetic reaction network that identifies 5 new core HMO structures. A comparison of monosaccharide compositions demonstrated that the model was able to discriminate between two possible groups of intermediates between major subnetworks, and to assign possible structures to several previously uncharacterised HMOs. The effect of enzyme knockouts is presented, identifying β-1,4-galactosyltransferase and β-1,3-N-acetylglucosaminyltransferase as key enzyme activities involved in the generation of the observed HMO glycosylation patterns. The model also provides a synthesis chassis for the most common HMOs found in lactating mothers.

Current Advances in Structure-Function Relationships and Dose-Dependent Effects of Human Milk Oligosaccharides

HMOs (human milk oligosaccharides) are the third most important nutrient in breast milk. As complex glycans, HMOs play an important role in regulating neonatal intestinal immunity, resisting viral and bacterial infections, displaying anti-inflammatory characteristics, and promoting brain development. Although there have been some previous reports of HMOs, a detailed literature review summarizing the structure-activity relationships and dose-dependent effects of HMOs is lacking. Hence, after introducing the structures and synthetic pathways of HMOs, this review summarizes and categorizes identified structure-function relationships of HMOs. Differential mechanisms of different structural HMOs utilization by microorganisms are summarized. This review also emphasizes the recent advances in the interactions between different health benefits and the variance of dosage effect based on in vitro cell tests, animal experiments, and human intervention studies. The potential relationships between the chemical structure, the dosage selection, and the physiological properties of HMOs as functional foods are vital for further understanding of HMOs and their future applications.

Glycomic and Glycoproteomic Techniques in Neurodegenerative Disorders and Neurotrauma: Towards Personalized Markers

The proteome represents all the proteins expressed by a genome, a cell, a tissue, or an organism at any given time under defined physiological or pathological circumstances. Proteomic analysis has provided unparalleled opportunities for the discovery of expression patterns of proteins in a biological system, yielding precise and inclusive data about the system. Advances in the proteomics field opened the door to wider knowledge of the mechanisms underlying various post-translational modifications (PTMs) of proteins, including glycosylation. As of yet, the role of most of these PTMs remains unidentified. In this state-of-the-art review, we present a synopsis of glycosylation processes and the pathophysiological conditions that might ensue secondary to glycosylation shortcomings. The dynamics of protein glycosylation, a crucial mechanism that allows gene and pathway regulation, is described. We also explain how-at a biomolecular level-mutations in glycosylation-related genes may lead to neuropsychiatric manifestations and neurodegenerative disorders. We then analyze the shortcomings of glycoproteomic studies, putting into perspective their downfalls and the different advanced enrichment techniques that emanated to overcome some of these challenges. Furthermore, we summarize studies tackling the association between glycosylation and neuropsychiatric disorders and explore glycoproteomic changes in neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Huntington disease, multiple sclerosis, and amyotrophic lateral sclerosis. We finally conclude with the role of glycomics in the area of traumatic brain injury (TBI) and provide perspectives on the clinical application of glycoproteomics as potential diagnostic tools and their application in personalized medicine.

Strategy for Isolation, Preparation, and Structural Analysis of Chondroitin Sulfate Oligosaccharides from Natural Sources

The structure of chondroitin sulfate oligosaccharides (CSOs), especially their sulfation pattern, has been found to be closely related with many biological pathways and diseases. However, detailed functional analysis such as their interaction with glycan binding proteins (GBPs) has been lagging, presumably due to the unavailability of well-defined, diverse structures. Besides challenging chemical and enzymatic synthesis, this is also due to the challenges in their purification at the isomer level and structural analysis owing to their instability, structural complexity, and low mass spectrometry detection sensitivity. Herein, we first used recycling preparative HPLC to separate and purify shark CS tetrasaccharide component labeled by a bifunctional fluorescent linker 2-amino-N-(2-aminoethyl)benzamide (AEAB) at the isomer level. Then, each isomer was derivatized through a multistage procedure including N-acetylation, carboxyl amidation, permethylation, and desulfation with silylating reagent. Structural analysis of each derivatized isomer was performed with ESI-MSⁿ in positive ion mode. A total of 16 isomers of CSO-AEAB were isolated, with a minimum mass component of 0.007 mg and a maximum mass component of 17.53 mg, of which 10 isomers (>90 μg) were structurally analyzed. This preparation and structure analysis of CSOs lay the foundation for further study of the structure-activity relationship of CSOs.

Amplification and Preparation of Cellular O-Glycomes for Functional Glycomics

Mucin-type O-glycans play key roles in many cellular processes, and they are often altered in human diseases. A major challenge in studying the role of O-glycans through functional O-glycomics is the absence of a complete repertoire of the glycans that comprise the human O-glycome. Here we describe a cellular O-glycome preparation strategy, Preparative Cellular O-Glycome Reporter/Amplification (pCORA), that introduces 4-N₃-Bn-GalNAc(Ac)₃ as a novel precursor in large-scale cell cultures to generate usable amounts of O-glycans as a potential O-glycome factory. Cultured human non-small cell lung cancer (NSCLC) A549 cells take up the precursor, which is extended by cellular glycosyltransferases to produce 4-N₃-Bn-α-O-glycans that are secreted into the culture medium. The O-glycan derivatives can be clicked with a fluorescent bifunctional tag that allows multidimensional HPLC purification and production of a tagged glycan library, representing the O-glycome of the corresponding cells. We obtained ∼5% conversion of precursor to O-glycans and purified a tagged O-glycan library of over 100 O-glycan derivatives, many of which were present in >100 nmol amounts and were sequenced by sequential MS fragmentation (MSⁿ). These O-glycans were successfully printed onto epoxy glass slides as an O-glycome shotgun microarray. We used this novel array to explore binding activity of serum IgM in healthy persons and NSCLC patients at different cancer stages. This novel strategy provides access to complex O-glycans in significant quantities and may offer a new route to discovery of potential diagnostic disease biomarkers.

Preparation of Complex Glycans From Natural Sources for Functional Study

One major barrier in glycoscience is the lack of diverse and biomedically relevant complex glycans in sufficient quantities for functional study. Complex glycans from natural sources serve as an important source of these glycans and an alternative to challenging chemoenzymatic synthesis. This review discusses preparation of complex glycans from several classes of glycoconjugates using both enzymatic and chemical release approaches. Novel technologies have been developed to advance the large-scale preparation of complex glycans from natural sources. We also highlight recent approaches and methods developed in functional and fluorescent tagging and high-performance liquid chromatography (HPLC) isolation of released glycans.

Advances in Tools to Determine the Glycan-Binding Specificities of Lectins and Antibodies

Proteins that bind carbohydrate structures can serve as tools to quantify or localize specific glycans in biological specimens. Such proteins, including lectins and glycan-binding antibodies, are particularly valuable if accurate information is available about the glycans that a protein binds. Glycan arrays have been transformational for uncovering rich information about the nuances and complexities of glycan-binding specificity. A challenge, however, has been the analysis of the data. Because protein-glycan interactions are so complex, simplistic modes of analyzing the data and describing glycan-binding specificities have proven inadequate in many cases. This review surveys the methods for handling high-content data on protein-glycan interactions. We contrast the approaches that have been demonstrated and provide an overview of the resources that are available. We also give an outlook on the promising experimental technologies for generating new insights into protein-glycan interactions, as well as a perspective on the limitations that currently face the field.

O-Benzylhydroxylamine (BHA) as a Cleavable Tag for Isolation and Purification of Reducing Glycans

Glycoscience has been recognized as an important area in biomedical research. Currently, a major obstacle for glycoscience study is the lack of diverse, biomedically relevant, and complex glycans in quantities sufficient for exploring their structural and functional aspects. Complementary to chemoenzymatic synthesis, natural glycans could serve as a great source of biomedically relevant glycans if they are available in sufficient quantities. We have recently developed oxidative release of natural glycans (ORNG) for large-scale release of N-glycans as free reducing glycans. While free reducing glycans can be readily derivatized with ultraviolet or fluorescent tags for high-performance liquid chromatography (HPLC) and mass spectrometry (MS) analysis, it is difficult to remove tags for the regeneration of free reducing glycans without affecting the structural integrity of glycans. To address this inconvenience, we explored the use of a cleavable tag, O-benzylhydroxylamine (BHA). Free reducing glycans are easily and efficiently labeled with BHA under mild conditions, enabling UV detection during HPLC purification. Individual glycan-BHA conjugates can then be separated using multidimensional HPLC and characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and MS/MS. The BHA tag can then be easily removed by palladium-on-carbon (Pd/C)-catalyzed hydrogenation to efficiently regenerate free reducing glycans with little effect on glycan structures. This procedure provides a simple and straightforward way to tag free reducing glycans for purification at a preparative scale using multidimensional HPLC and subsequently recover purified free reducing glycans.

Glycan Microarrays as Chemical Tools for Identifying Glycan Recognition by Immune Proteins

Glycans and glycan binding proteins (GBPs or lectins) are essential components in almost every aspect of immunology. Investigations of the interactions between glycans and GBPs have greatly advanced our understanding of the molecular basis of these fundamental immunological processes. In order to better study the glycan-GBP interactions, microscope glass slide-based glycan microarrays were conceived and proved to be an incredibly useful and successful tool. A variety of methods have been developed to better present the glycans so that they mimic natural presentations. Breakthroughs in chemical biology approaches have also made available glycans with sophisticated structures that were considered practically impossible just a few decade ago. Glycan microarrays provide a wealth of valuable information in immunological studies. They allow for discovery of detailed glycan binding preferences or novel binding epitopes of known endogenous immune receptors, which can potentially lead to the discovery of natural ligands that carry the glycans. Glycan microarrays also serve as a platform to discover new GBPs that are vital to the process of infection and invasion by microorganisms. This review summarizes the construction strategies and the immunological applications of glycan microarrays, particularly focused on those with the most comprehensive sets of glycan structures. We also review new methods and technologies that have evolved. We believe that glycan microarrays will continue to benefit the growing research community with various interests in the field of immunology.

Effects of Child and Maternal Histo-Blood Group Antigen Status on Symptomatic and Asymptomatic Enteric Infections in Early Childhood

BACKGROUND

Histo-blood group antigens (HBGAs) such as fucosyltransferase (FUT)2 and 3 may act as innate host factors that differentially influence susceptibility of individuals and their offspring to pediatric enteric infections.

METHODS

In 3 community-based birth cohorts, FUT2 and FUT3 statuses were ascertained for mother-child dyads. Quantitative polymerase chain reaction panels tested 3663 diarrheal and 18 148 asymptomatic stool samples for 29 enteropathogens. Cumulative diarrhea and infection incidence were compared by child (n = 520) and mothers' (n = 519) HBGA status and hazard ratios (HRs) derived for all-cause diarrhea and specific enteropathogens.

RESULTS

Children of secretor (FUT2 positive) mothers had a 38% increased adjusted risk of all-cause diarrhea (HR = 1.38; 95% confidence interval (CI), 1.15-1.66) and significantly reduced time to first diarrheal episode. Child FUT2 and FUT3 positivity reduced the risk for all-cause diarrhea by 29% (HR = 0.81; 95% CI, 0.71-0.93) and 27% (HR = 0.83; 95% CI, 0.74-0.92), respectively. Strong associations between HBGAs and pathogen-specific infection and diarrhea were observed, particularly for noroviruses, rotaviruses, enterotoxigenic Escherichia coli, and Campylobacter jejuni/coli.

CONCLUSIONS

Histo-blood group antigens affect incidence of all-cause diarrhea and enteric infections at magnitudes comparable to many common disease control interventions. Studies measuring impacts of interventions on childhood enteric disease should account for both child and mothers' HBGA status.

History and future of shotgun glycomics

Glycans in polysaccharides and glycoconjugates of the hydrophilic exterior of all animal cells participate in signal transduction, cellular adhesion, intercellular signaling, and sites for binding of pathogens largely through protein–glycan interactions. Microarrays of defined glycans have been used to study the binding specificities of biologically relevant glycan-binding proteins (GBP), but such arrays are limited by their lack of diversity or relevance to the GBP being investigated. Shotgun glycan microarrays are made up of structurally undefined glycans that were released from natural sources, labeled with bifunctional reagents so that they can be monitored during their purification using multidimensional chromatographic procedures, stored as a tagged glycan library (TGL) and subsequently printed onto microarrays at equal molar concentrations. The shotgun glycan microarray is then interrogated with a biologically relevant GBP and the corresponding glycan ligands can be retrieved from the TGL for detailed structural analysis and further functional analysis. Shotgun glycomics extended the defined glycan microarray to a discovery platform that supports functional glycomic analyses and may provide a useful process for ultimately defining the human glycome.

Glycan recognition in globally dominant human rotaviruses

Rotaviruses (RVs) cause life-threatening diarrhea in infants and children worldwide. Recent biochemical and epidemiological studies underscore the importance of histo-blood group antigens (HBGA) as both cell attachment and susceptibility factors for the globally dominant P[4], P[6], and P[8] genotypes of human RVs. How these genotypes interact with HBGA is not known. Here, our crystal structures of P[4] and a neonate-specific P[6] VP8*s alone and in complex with H-type I HBGA reveal a unique glycan binding site that is conserved in the globally dominant genotypes and allows for the binding of ABH HBGAs, consistent with their prevalence. Remarkably, the VP8* of P[6] RVs isolated from neonates displays subtle structural changes in this binding site that may restrict its ability to bind branched glycans. This provides a structural basis for the age-restricted tropism of some P[6] RVs as developmentally regulated unbranched glycans are more abundant in the neonatal gut.

Human rotaviruses (RV) bind to histo-blood group antigens (HBGA) for attachment, but how different viral genotypes interact with HBGA isn’t known. Here, Hu et al. report crystal structures of a prevalent and a neonate-specific RV in complex with HBGA and provide insights into glycan recognition and age-restricted tropism of RVs.

Human Milk Oligosaccharides as Promising Antivirals

Human milk oligosaccharides (HMOs) are diverse unconjugated carbohydrates that are highly abundant in human breast milk. These glycans are investigated in the context of exhibiting multiple functions in infant growth and development. They seem to provide protection against infectious diseases, including a number of poorly manageable viral infections. Although the potential mechanism of the HMO antiviral protection is rather broad, much of the current experimental work has focused on studying of HMO antiadhesive properties. HMOs may mimic structures of viral receptors and block adherence to target cells, thus preventing infection. Still, the potential of HMOs as a source for new antiviral drugs is relatively unexploited. This can be partly attributed to the extreme complexity of the virus-carbohydrate interactions and technical difficulties in HMO isolation, characterization, and manufacturing procedures. Fortunately, we are currently entering a period of major technological advances that have enabled deeper insights into carbohydrate mediated viral entry, rational selection of HMOs as anti-entry inhibitors, and even evaluation of individual synthetic HMO structures. Here, we provide an up-to-date review on glycan binding studies for rotaviruses, noroviruses, influenza viruses, and human immunodeficiency viruses. We also discuss the preventive and therapeutic potential of HMOs as anti-entry inhibitors and address challenges on the route from fundamental studies to clinical trials.

Ion Mobility Spectrometry-Mass Spectrometry Coupled with Gas-Phase Hydrogen/Deuterium Exchange for Metabolomics Analyses

Ion mobility spectrometry-mass spectrometry (IMS-MS) in combination with gas-phase hydrogen/deuterium exchange (HDX) and collision-induced dissociation (CID) is evaluated as an analytical method for small-molecule standard and mixture characterization. Experiments show that compound ions exhibit unique HDX reactivities that can be used to distinguish different species. Additionally, it is shown that gas-phase HDX kinetics can be exploited to provide even further distinguishing capabilities by using different partial pressures of reagent gas. The relative HDX reactivity of a wide variety of molecules is discussed in light of the various molecular structures. Additionally, hydrogen accessibility scoring (HAS) and HDX kinetics modeling of candidate (in silico) ion structures is utilized to estimate the relative ion conformer populations giving rise to specific HDX behavior. These data interpretation methods are discussed with a focus on developing predictive tools for HDX behavior. Finally, an example is provided in which ion mobility information is supplemented with HDX reactivity data to aid identification efforts of compounds in a metabolite extract. Graphical Abstract ᅟ.

Systematic review of the concentrations of oligosaccharides in human milk

Context

Oligosaccharides are the third largest solid component in human milk. These diverse compounds are thought to have numerous beneficial functions in infants, including protection against infectious diseases. The structures of more than 100 oligosaccharides in human milk have been elucidated so far.

Objective

The aim of this review was to identify the main factors that affect the concentrations of oligosaccharides in human milk and to determine whether it is possible to calculate representative and reliable mean concentrations.

Data Sources

A comprehensive literature search on oligosaccharide concentrations in human milk was performed in 6 electronic databases: BIOSIS, Current Contents Search, Embase, Lancet Titles, MEDLINE and PubMed.

Study Selection

The initial search resulted in 1363 hits. After the elimination of duplicates, the literature was screened. The application of strict inclusion criteria resulted in 21 articles selected.

Data Extraction

Oligosaccharide concentrations, both mean values and single values, reported in the literature were sorted by gestational age, secretor status of mothers, and defined lactation periods.

Results

Mean concentrations, including confidence limits, of 33 neutral and acidic oligosaccharides reported could be calculated. Concentrations of oligosaccharides in human milk show variations that are dependent on both the secretor type of the mother and the lactation period as examined by analyses of variance. In addition, large interlaboratory variations in the data were observed.

Conclusions

Worldwide interlaboratory quantitative analyses of identical milk samples would be required to identify the most reliable methods of determining concentrations of oligosaccharides in human milk. The data presented here contribute to the current knowledge about the composition and quantities of oligosaccharides in human milk and may foster greater understanding of the biological functions of these compounds.

High-Throughput Label- and Immobilization-Free Screening of Human Milk Oligosaccharides Against Lectins

The intense interest in the mechanisms responsible for the beneficial effects of breast-feeding on infant health has created a significant need for analytical methods capable of rapidly identifying interactions between human milk oligosaccharides (HMOs) and their protein receptors. Currently, there are no established, high-throughput assays for the screening libraries of free (unmodified) HMOs against lectins. The present work describes a rapid and label- and immobilization-free assay, based on catch-and-release electrospray ionization mass spectrometry (CaR-ESI-MS), capable of simultaneously screening mixtures of free HMOs of known concentration for binding to lectins in vitro. Ligand identification relies on the molecular weights (MWs), ion mobility separation arrival times, and collision-induced dissociation fingerprints of HMO anions released from the target protein in the gas phase. To establish the reliability of the assay, a library of 31 free HMOs, ranging in size from tri- to octasaccharide, was screened against three human galectin (hGal) proteins (a stable mutant of hGal1 (hGal-1), a C-terminal fragment of hGal-3 (hGal-3C) and hGal-7), with known HMO affinities. When implemented using an equimolar concentration library, the CaR-ESI-MS assay identified 100% of ligands with affinities >500 M^-1 and ≥93% of all HMO ligands (hGal-1-31 of 31 ligands; hGal-3C-25 of 25; hGal-7-28 of 30); no false positives were detected. The assay also successfully identified the majority of the highest affinity HMO ligands (or isomer sets that contain the highest affinity ligands) in the library for each of the three hGal. Notably, for each lectin, CaR-ESI-MS screening required <1 h to complete and consumed <5 ng of each HMO and <0.5 μg of protein.

Synthesis of asymmetrical multiantennary human milk oligosaccharides

Despite mammalian glycans typically having highly complex asymmetrical multiantennary architectures, chemical and chemoenzymatic synthesis has almost exclusively focused on the preparation of simpler symmetrical structures. This deficiency hampers investigations into the biology of glycan-binding proteins, which in turn complicates the biomedical use of this class of biomolecules. Herein, we describe an enzymatic strategy, using a limited number of human glycosyltransferases, to access a collection of 60 asymmetric, multiantennary human milk oligosaccharides (HMOs), which were used to develop a glycan microarray. Probing the array with several glycan-binding proteins uncovered that not only terminal glycoepitopes but also complex architectures of glycans can influence binding selectivity in unanticipated manners. N- and O-linked glycans express structural elements of HMOs, and thus, the reported synthetic principles will find broad applicability.

Human Milk Oligosaccharide Specificities of Human Galectins. Comparison of Electrospray Ionization Mass Spectrometry and Glycan Microarray Screening Results

The affinities of thirty-two free human milk oligosaccharides (HMOs) for four human galectin proteins, a stable mutant of hGal1 (hGal-1), a C-terminal fragment of hGal-3 (hGal-3C), hGal-7, and an N-terminal fragment of hGal-9 (hGal-9N), were measured using electrospray ionization mass spectrometry (ESI-MS). The binding data show that each of the four galectins recognize the majority of the HMOs tested (hGal-1 binds thirty-two HMOs, hGal-3C binds twenty-six, hGal-7 binds thirty-one, and hGal-9N binds twenty-six). Twenty-five of the HMOs tested bind all four galectins, with affinities ranging from 10³ to 10⁵ M^-1. The reliability of the ESI-MS assay for quantifying the affinities of HMOs for lectins was established from the agreement found between the ESI-MS data and affinities of a small number of HMOs for hGal-1, hGal-3C, and hGal-7 measured by isothermal titration calorimetry (ITC). Comparison of the relative affinities (of 14 HMOs) measured by ESI-MS with the reported specificities of hGal-1, hGal-3, hGal-7, and hGal-9 for these same HMOs established using the shotgun human milk glycan microarray (HM-SGM-v2) showed fair-to-poor correlation, with evidence of false positives and false negatives in the microarray data. The results of this study suggest that HMO specificities of lectins established using microarrays may not accurately reflect their true HMO-binding properties and that the use of "in solution" assays such as ESI-MS and ITC is to be preferred.

Characterization of IgG glycosylation in rheumatoid arthritis patients by MALDI-TOF-MSn and capillary electrophoresis

An analytical method based on the combination of multistage mass spectrometry (MSⁿ) and capillary electrophoresis (CE) was developed for the analysis of immunoglobulin G (IgG) glycosylation in rheumatoid arthritis (RA) patients. It has been recently suggested that IgG glycosylation defect may be involved in RA immunopathogenesis. Complete characterization of glycans, including both qualitative and quantitative analysis, requires a combination of different techniques, and accurate, robust, sensitive, and high-throughput methodologies are important for analysis of clinical samples. In the present study, N-glycosylation of IgG in RA patients and in healthy people was characterized through identification of the released glycans using multistage matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MSⁿ), and quantitation by CE. Assignment of the IgG N-glycan structures was made through branching pattern analysis by MSⁿ with high-throughput. Further accurate quantitation indicated that galactosylation and sialylation of IgG N-glycans in RA cases were significantly lower than in healthy subjects. The results indicate that CE coupled with MSⁿ can identify abnormal glycosylation of IgG in RA patients compared with healthy people, and that the present work is useful for RA mechanism studies and RA diagnosis. Graphical Abstract Qualitative and quantitative analysis of IgG glycosylation in rheumatoid arthritis patients by MALDI-TOF-MSⁿ and capillary electrophoresis.

Divergent Chemoenzymatic Synthesis of Asymmetrical-Core-Fucosylated and Core-Unmodified N-Glycans

A divergent chemoenzymaytic approach for the preparation of core-fucosylated and core-unmodified asymmetrical N-glycans from a common advances precursor is described. An undecasaccharide was synthesized by sequential chemical glycosylations of an orthogonally protected core fucosylated hexasaccharide that is common to all mammalian core fucosylated N-glycans. Antennae-selective enzymatic extension of the undecasaccharide using a panel of glycosyl transferases afforded core fucosylated asymmetrical triantennary N-glycan isomers, which are potential biomarkers for breast cancer. A unique aspect of our approach is that a fucosidase (FucA1) has been identified that selectively can cleave a core-fucoside without affecting the fucoside of a sialyl LewisX epitope to give easy access to core-unmodified compounds.

Characterizing Protein Glycosylation through On-Chip Glycan Modification and Probing

Glycans are critical to protein biology and are useful as disease biomarkers. Many studies of glycans rely on clinical specimens, but the low amount of sample available for some specimens limits the experimental options. Here we present a method to obtain information about protein glycosylation using a minimal amount of protein. We treat proteins that were captured or directly spotted in small microarrays (2.2 mm × 2.2 mm) with exoglycosidases to successively expose underlying features, and then we probe the native or exposed features using a panel of lectins or glycan-binding reagents. We developed an algorithm to interpret the data and provide predictions about the glycan motifs that are present in the sample. We demonstrated the efficacy of the method to characterize differences between glycoproteins in their sialic acid linkages and N-linked glycan branching, and we validated the assignments by comparing results from mass spectrometry and chromatography. The amount of protein used on-chip was about 11 ng. The method also proved effective for analyzing the glycosylation of a cancer biomarker in human plasma, MUC5AC, using only 20 μL of the plasma. A glycan on MUC5AC that is associated with cancer had mostly 2,3-linked sialic acid, whereas other glycans on MUC5AC had a 2,6 linkage of sialic acid. The on-chip glycan modification and probing (on-chip GMAP) method provides a platform for analyzing protein glycosylation in clinical specimens and could complement the existing toolkit for studying glycosylation in disease.

Isomeric complexity of glycosylation documented by MSn

Re-analysis of two breast cancer cell lines, MCF-7 and MDA-MB-231, has shown multiple isomeric structures exposed by sequential mass spectrometry, MS ⁿ . Several released glycan compositions were re-evaluated, which indicated variations in polylactosamine and fucosylation structures. Probable isomer numbers, when considering both stereo and structural entities, are significant and the varying types are mentioned. The structural isomers of linkage position are most frequently considered, while stereo isomers are usually assumed from biosynthetic data. Evaluation of any new sample should be cautious and merits careful attention to empirical data. While isomers are usually considered a chromatographic problem (e.g., LCMS, IMMS) and most frequently considered a separations problem, such results will always be challenged by identification and documentation. MSⁿ data provide a direct spatial solution that includes spectral data for characterization (mass and abundance) supported by a universal library match feature.

Histo-blood group glycans in the context of personalized medicine

BACKGROUND

A subset of histo-blood group antigens including ABO and Lewis are oligosaccharide structures which may be conjugated to lipids or proteins. They are known to be important recognition motifs not only in the context of blood transfusions, but also in infection and cancer development.

SCOPE OF REVIEW

Current knowledge on the molecular background and the implication of histo-blood group glycans in the prevention and therapy of infectious and non-communicable diseases, such as cancer and cardiovascular disease, is presented.

MAJOR CONCLUSIONS

Glycan-based histo-blood groups are associated with intestinal microbiota composition, the risk of various diseases as well as therapeutic success of, e.g., vaccination. Their potential as prebiotic or anti-microbial agents, as disease biomarkers and vaccine targets should be further investigated in future studies. For this, recent and future technological advancements will be of particular importance, especially with regard to the unambiguous structural characterization of the glycan portion in combination with information on the protein and lipid carriers of histo-blood group-active glycans in large cohorts.

GENERAL SIGNIFICANCE

Histo-blood group glycans have a unique linking position in the complex network of genes, oncodevelopmental biological processes, and disease mechanisms. Thus, they are highly promising targets for novel approaches in the field of personalized medicine. This article is part of a Special Issue entitled "Glycans in personalised medicine" Guest Editor: Professor Gordan Lauc.

Oxidative release of natural glycans for functional glycomics

Glycans have essential roles in biology and the etiology of many diseases. A major hurdle in studying glycans through functional glycomics is the lack of methods to release glycans from diverse types of biological samples. Here we describe an oxidative strategy using household bleach to release all types of free reducing N-glycans and O-glycan-acids from glycoproteins, and glycan nitriles from glycosphingolipids. Released glycans are directly useful in glycomic analyses and can be derivatized fluorescently for functional glycomics. This chemical method overcomes the limitations in glycan generation and promotes archiving and characterization of human and animal glycomes and their functions.

Galectins are human milk glycan receptors

The biological recognition of human milk glycans (HMGs) is poorly understood. Because HMGs are rich in galactose we explored whether they might interact with human galectins, which bind galactose-containing glycans and are highly expressed in epithelial cells and other cell types. We screened a number of human galectins for their binding to HMGs on a shotgun glycan microarray consisting of 247 HMGs derived from human milk, as well as to a defined HMG microarray. Recombinant human galectins (hGal)-1, -3, -4, -7, -8 and -9 bound selectively to glycans, with each galectin recognizing a relatively unique binding motif; by contrast hGal-2 did not recognize HMGs, but did bind to the human blood group A Type 2 determinants on other microarrays. Unlike other galectins, hGal-7 preferentially bound to glycans expressing a terminal Type 1 (Galβ1-3GlcNAc) sequence, a motif that had eluded detection on non-HMG glycan microarrays. Interactions with HMGs were confirmed in a solution setting by isothermal titration microcalorimetry and hapten inhibition experiments. These results demonstrate that galectins selectively bind to HMGs and suggest the possibility that galectin-HMG interactions may play a role in infant immunity.

Human DC-SIGN binds specific human milk glycans

Human milk glycans (HMGs) are prebiotics, pathogen receptor decoys and regulators of host physiology and immune responses. Mechanistically, human lectins (glycan-binding proteins, hGBP) expressed by dendritic cells (DCs) are of major interest, as these cells directly contact HMGs. To explore such interactions, we screened many C-type lectins and sialic acid-binding immunoglobulin-like lectins (Siglecs) expressed by DCs for glycan binding on microarrays presenting over 200 HMGs. Unexpectedly, DC-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) showed robust binding to many HMGs, whereas other C-type lectins failed to bind, and Siglec-5 and Siglec-9 showed weak binding to a few glycans. By contrast, most hGBP bound to multiple glycans on other microarrays lacking HMGs. An α-linked fucose residue was characteristic of HMGs bound by DC-SIGN. Binding of DC-SIGN to the simple HMGs 2'-fucosyl-lactose (2'-FL) and 3-fucosyl-lactose (3-FL) was confirmed by flow cytometry to beads conjugated with 2'-FL or 3-FL, as well as the ability of the free glycans to inhibit DC-SIGN binding. 2'-FL had an IC50 of ∼1 mM for DC-SIGN, which is within the physiological concentration of 2'-FL in human milk. These results demonstrate that DC-SIGN among the many hGBP expressed by DCs binds to α-fucosylated HMGs, and suggest that such interactions may be important in influencing immune responses in the developing infant.

Diversity in Rotavirus-Host Glycan Interactions: A "Sweet" Spectrum

Interaction with cellular glycans is a critical initial step in the pathogenesis of many infectious agents. Technological advances in glycobiology have expanded the repertoire of studies delineating host glycan-pathogen interactions. For rotavirus, the VP8* domain of the outer capsid spike protein VP4 is known to interact with cellular glycans. Sialic acid was considered the key cellular attachment factor for rotaviruses for decades. Although this is true for many rotavirus strains causing infections in animals, glycan array screens show that many human rotavirus strains bind nonsialylated glycoconjugates, called histo-blood group antigens, in a strain-specific manner. The expression of histo-blood group antigens is determined genetically and is regulated developmentally. Variations in glycan binding between different rotavirus strains are biologically relevant and provide new insights into multiple aspects of virus pathogenesis such as interspecies transmission, host range restriction, and tissue tropism. The genetics of glycan expression may affect susceptibility to different rotavirus strains and vaccine viruses, and impact the efficacy of rotavirus vaccination in different populations. A multidisciplinary approach to understanding rotavirus-host glycan interactions provides molecular insights into the interaction between microbial pathogens and glycans, and opens up new avenues to translate findings from the bench to the human population.

Computational approaches to define a human milk metaglycome

MOTIVATION

The goal of deciphering the human glycome has been hindered by the lack of high-throughput sequencing methods for glycans. Although mass spectrometry (MS) is a key technology in glycan sequencing, MS alone provides limited information about the identification of monosaccharide constituents, their anomericity and their linkages. These features of individual, purified glycans can be partly identified using well-defined glycan-binding proteins, such as lectins and antibodies that recognize specific determinants within glycan structures.

RESULTS

We present a novel computational approach to automate the sequencing of glycans using metadata-assisted glycan sequencing, which combines MS analyses with glycan structural information from glycan microarray technology. Success in this approach was aided by the generation of a 'virtual glycome' to represent all potential glycan structures that might exist within a metaglycomes based on a set of biosynthetic assumptions using known structural information. We exploited this approach to deduce the structures of soluble glycans within the human milk glycome by matching predicted structures based on experimental data against the virtual glycome. This represents the first meta-glycome to be defined using this method and we provide a publically available web-based application to aid in sequencing milk glycans.

AVAILABILITY AND IMPLEMENTATION

http://glycomeseq.emory.edu

CONTACT

sagravat@bidmc.harvard.edu

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Schistosoma mansoni α1,3-fucosyltransferase-F generates the Lewis X antigen

Genetic evidence suggests that the Schistosoma mansoni genome contains six genes that encode α1,3-fucosyltransferases (smFuTs). To date, the activities and specificities of these putative fucosyltransferases are unknown. As Schistosoma express a variety of fucosylated glycans, including the Lewis X antigen Galβ1-4(Fucα1-3)GlcNAcβ-R, it is likely that this family of genes encode enzymes that are partly responsible for the generation of those structures. Here, we report the molecular cloning of fucosyltransferase-F (smFuT-F) from S. mansoni, as a soluble, green fluorescent protein fusion protein and its acceptor specificity. The gene smFuT-F was expressed in HEK freestyle cells, purified by affinity chromatography, and analyzed toward a broad panel of glycan acceptors. The enzyme product of smFuT-F effectively utilizes a type II chain acceptor Galβ1-4GlcNAc-R, but notably not the LDN sequence GalNAcβ1-4GlcNAc-R, to generate Lewis X type-glycans, and smFuT-F transcripts are present in all intramammalian life stages.

Structural basis of glycan specificity in neonate-specific bovine-human reassortant rotavirus

Strain-dependent variation of glycan recognition during initial cell attachment of viruses is a critical determinant of host specificity, tissue-tropism and zoonosis. Rotaviruses (RVs), which cause life-threatening gastroenteritis in infants and children, display significant genotype-dependent variations in glycan recognition resulting from sequence alterations in the VP8* domain of the spike protein VP4. The structural basis of this genotype-dependent glycan specificity, particularly in human RVs, remains poorly understood. Here, from crystallographic studies, we show how genotypic variations configure a novel binding site in the VP8* of a neonate-specific bovine-human reassortant to uniquely recognize either type I or type II precursor glycans, and to restrict type II glycan binding in the bovine counterpart. Such a distinct glycan-binding site that allows differential recognition of the precursor glycans, which are developmentally regulated in the neonate gut and abundant in bovine and human milk provides a basis for age-restricted tropism and zoonotic transmission of G10P[11] rotaviruses.

Glycan microarrays of fluorescently-tagged natural glycans

This review discusses the challenges facing research in 'functional glycomics' and the novel technologies that are being developed to advance the field. The structural complexity of glycans and glycoconjugates makes studies of both their structures and recognition difficult. However, these intricate structures can be captured from their natural sources, isolated and fluorescently-tagged for detailed structural analysis and for presentation on glycan microarrays for functional recognition by glycan-binding proteins. These advances in glycan preparation and manipulation enable the streamlining of functional glycomics studies and will help to propel the field forward in studying natural, biologically relevant glycans.

Unravelling glucan recognition systems by glycome microarrays using the designer approach and mass spectrometry

Glucans are polymers of d-glucose with differing linkages in linear or branched sequences. They are constituents of microbial and plant cell-walls and involved in important bio-recognition processes, including immunomodulation, anticancer activities, pathogen virulence, and plant cell-wall biodegradation. Translational possibilities for these activities in medicine and biotechnology are considerable. High-throughput micro-methods are needed to screen proteins for recognition of specific glucan sequences as a lead to structure–function studies and their exploitation. We describe construction of a “glucome” microarray, the first sequence-defined glycome-scale microarray, using a “designer” approach from targeted ligand-bearing glucans in conjunction with a novel high-sensitivity mass spectrometric sequencing method, as a screening tool to assign glucan recognition motifs. The glucome microarray comprises 153 oligosaccharide probes with high purity, representing major sequences in glucans. Negative-ion electrospray tandem mass spectrometry with collision-induced dissociation was used for complete linkage analysis of gluco-oligosaccharides in linear “homo” and “hetero” and branched sequences. The system is validated using antibodies and carbohydrate-binding modules known to target α- or β-glucans in different biological contexts, extending knowledge on their specificities, and applied to reveal new information on glucan recognition by two signaling molecules of the immune system against pathogens: Dectin-1 and DC-SIGN. The sequencing of the glucan oligosaccharides by the MS method and their interrogation on the microarrays provides detailed information on linkage, sequence and chain length requirements of glucan-recognizing proteins, and are a sensitive means of revealing unsuspected sequences in the polysaccharides.