Modifications of glycans: biological significance and therapeutic opportunities

The main sources of molecular organization in the cell. Atlas of self-organized and self-regulated dynamic biostructures

One of the most important goals of contemporary biology is to understand the principles of the molecular order underlying the complex dynamic architecture of cells. Here, we present an overview of the main driving forces involved in the cellular molecular complexity and in the emergent functional dynamic structures, spanning from the most basic molecular organization levels to the complex emergent integrative systemic behaviors. First, we address the molecular information processing which is essential in many complex fundamental mechanisms such as the epigenetic memory, alternative splicing, regulation of transcriptional system, and the adequate self-regulatory adaptation to the extracellular environment. Next, we approach the biochemical self-organization, which is central to understand the emergency of metabolic rhythms, circadian oscillations, and spatial traveling waves. Such a complex behavior is also fundamental to understand the temporal compartmentalization of the cellular metabolism and the dynamic regulation of many physiological activities. Numerous examples of biochemical self-organization are considered here, which show that practically all the main physiological processes in the cell exhibit this type of dynamic molecular organization. Finally, we focus on the biochemical self-assembly which, at a primary level of organization, is a basic but important mechanism for the order in the cell allowing biomolecules in a disorganized state to form complex aggregates necessary for a plethora of essential structures and physiological functions. In total, more than 500 references have been compiled in this review. Due to these main sources of order, systemic functional structures emerge in the cell, driving the metabolic functionality towards the biological complexity.

Bioinformatics-Facilitated Identification of Novel Bacterial Sulfoglycosidases That Hydrolyze 6-Sulfo-N-acetylglucosamine

Glycan sulfation is a widespread postglycosylation modification crucial for modulating biological functions including cellular adhesion, signaling, and bacterial colonization. 6-Sulfo-β-GlcNAcases are a class of enzyme that alters sulfation patterns. Such changes in sulfation patterns are linked to diseases such as bowel inflammation, colitis, and cancer. Despite their significance, 6-sulfo-β-GlcNAcases, which cleave β-linked 6-sulfo-N-acetylglucosamine (6S-GlcNAc), have been but rarely identified. This scarcity results mainly from the short, diverse, and distinctive sulfate-binding motifs required for recognition of the 6-sulfate group in 6S-GlcNAc in addition to the conserved GH20 family features. In this study, we discovered 6-sulfo-β-GlcNAcases and assigned two novel sulfate-binding motifs by the use of comparative genomics, structural predictions, and activity-based screening. Our findings expand the known microbiota capable of degrading sulfated glycans and add significant enzymes to the tool kit for analysis and synthesis of sulfated oligosaccharides.

The Effect of Hyperconjugation and Hydrogen Bonding on the Conformers of Methylated Monosaccharides

The conformational landscapes of four 1-O-methylated monosaccharides-methyl α-glucose, methyl β-glucose, methyl α-galactose, and methyl β-galactose-were characterized using jet-cooled broadband rotational spectroscopy, supported by density functional theory calculations. A newly designed, simple pulsed nozzle assembly was used to introduce the sugar samples into a jet expansion without thermal degradation, eliminating the need for a complex and expensive laser ablation system. Ten conformers were experimentally identified by assigning their rotational spectra, and the intricate methyl internal rotation splittings were analysed. Notably, methylation alters the directionality of intramolecular hydrogen bonding of α-galactose highlighting its impact on structural preference. Natural bond orbital, intrinsic bond strength, and non-covalent interaction analyses were conducted to explore the interplay between hydrogen bonding and hyperconjugation. A set of σ to σ* neutral hyperconjugative interactions was found to override a strong hydrogen bond, driving a preference for the gauche conformers.

Enzyme-Sialylation-Controlled Chemical Sulfation of Glycan Epitopes for Decoding the Binding of Siglec Ligands

Widely distributed in nature, sulfated glycan epitopes play important roles in diverse pathophysiological processes. However, due to their structural complexity, the preparation of glycan epitopes with structurally defined sulfation patterns is challenging, which significantly hampers the detailed elucidation of their biological functions at the molecular level. Here, we introduce a strategy for site-specific chemical sulfation of glycan epitopes, leveraging enzymatic sialylation and desialylation processes to precisely control the regio-specificity of sulfation of disaccharide or trisaccharide glycan backbones. Using this method, a sulfated glycan library covering the most common sialylated glycan epitopes was prepared in high yield and efficiency. By screening a microarray prepared with this glycan library, we systematically probed their binding specificity with human Siglecs (sialic acid-binding immunoglobulin-type lectins), many of which function as glyco-immune checkpoints to suppress immune system activation. Our investigation revealed that sulfation and sialylation patterns serve as important determinants of Siglec binding affinity and specificity. Thus, these findings offer new insights for the development of research tools and potential therapeutic agents targeting glyco-immune checkpoints by modulating the Siglec signaling pathway.

TREK2 Lipid Binding Preferences Revealed by Native Mass Spectrometry

TREK2, a two-pore domain potassium channel, is recognized for its regulation by various stimuli, including lipids. While previous members of the TREK subfamily, TREK1 and TRAAK, have been investigated to elucidate their lipid affinity and selectivity, TREK2 has not been similarly studied in this regard. Our findings indicate that while TRAAK and TREK2 exhibit similarities in terms of electrostatics and share an overall structural resemblance, there are notable distinctions in their interaction with lipids. Specifically, SAPI(4,5)P2,1-stearoyl-2-arachidonoyl-sn-glycero-3-phospho-(1'-myo-inositol-4',5'-bisphosphate) exhibits a strong affinity for TREK2, surpassing that of dOPI(4,5)P2,1,2-dioleoyl-sn-glycero-3-phospho-(1'-myo-inositol-4',5'-bisphosphate), which differs in its acyl chains. TREK2 displays lipid binding preferences not only for the headgroup of lipids but also toward the acyl chains. Functional studies draw a correlation for lipid binding affinity and activity of the channel. These findings provide important insight into elucidating the molecular prerequisites for specific lipid binding to TREK2 important for function.

Recent advances in microscale separation techniques for glycome analysis

The glycomic analysis holds significant appeal due to the diverse roles that glycans and glycoconjugates play, acting as modulators and mediators in cellular interactions, cell/organism structure, drugs, energy sources, glyconanomaterials, and more. The glycomic analysis relies on liquid-phase separation technologies for molecular purification, separation, and identification. As a miniaturized form of liquid-phase separation technology, microscale separation technologies offer various advantages such as environmental friendliness, high resolution, sensitivity, fast speed, and integration capabilities. For glycan analysis, microscale separation technologies are continuously evolving to address the increasing challenges in their unique manners. This review discusses the fundamentals and applications of microscale separation technologies for glycomic analysis. It covers liquid-phase separation technologies operating at scales generally less than 100 µm, including capillary electrophoresis, nanoflow liquid chromatography, and microchip electrophoresis. We will provide a brief overview of glycomic analysis and describe new strategies in microscale separation and their applications in glycan analysis from 2014 to 2023.

Nanopore-based glycan sequencing: state of the art and future prospects

Sequencing of biomacromolecules is a crucial cornerstone in life sciences. Glycans, one of the fundamental biomolecules, derive their physiological and pathological functions from their structures. Glycan sequencing faces challenges due to its structural complexity and current detection technology limitations. As a highly sensitive sensor, nanopores can directly convert nucleic acid sequence information into electrical signals, spearheading the revolution of third-generation nucleic acid sequencing technologies. However, their potential for deciphering complex glycans remains untapped. Initial attempts demonstrated the significant sensitivity of nanopores in glycan sensing, which provided the theoretical basis and insights for the realization of nanopore-based glycan sequencing. Here, we present three potential technical routes to employ nanopore technology in glycan sequencing for the first time. The three novel technical routes include: strand sequencing, capturing glycan chains as they translocate through nanopores; sequential hydrolysis sequencing, capturing released monosaccharides one by one; splicing sequencing, mapping signals from hydrolyzed glycan fragments to an oligosaccharide database/library. Designing suitable nanopores, enzymes, and motors, and extracting characteristic signals pose major challenges, potentially aided by artificial intelligence. It would be highly desirable to design an all-in-one high-throughput glycan sequencer instrument by integrating a sample processing unit, nanopore array, and signal acquisition system into a microfluidic device. The nanopore sequencer invention calls for intensive multidisciplinary cooperation including electrochemistry, glycochemistry, engineering, materials, enzymology, etc. Advancing glycan sequencing will promote the development of basic research and facilitate the discovery of glycan-based drugs and disease markers, fostering progress in glycoscience and even life sciences.

The Exploitation of the Glycosylation Pattern in Asthma: How We Alter Ancestral Pathways to Develop New Treatments

Asthma has reached epidemic levels, yet progress in developing specific therapies is slow. One of the main reasons for this is the fact that asthma is an umbrella term for various distinct subsets. Due to its high heterogeneity, it is difficult to establish biomarkers for each subset of asthma and to propose endotype-specific treatments. This review focuses on protein glycosylation as a process activated in asthma and ways to utilize it to develop novel biomarkers and treatments. We discuss known and relevant glycoproteins whose functions control disease development. The key role of glycoproteins in processes integral to asthma, such as inflammation, tissue remodeling, and repair, justifies our interest and research in the field of glycobiology. Altering the glycosylation states of proteins contributing to asthma can change the pathological processes that we previously failed to inhibit. Special emphasis is placed on chitotriosidase 1 (CHIT1), an enzyme capable of modifying LacNAc- and LacdiNAc-containing glycans. The expression and activity of CHIT1 are induced in human diseased lungs, and its pathological role has been demonstrated by both genetic and pharmacological approaches. We propose that studying the glycosylation pattern and enzymes involved in glycosylation in asthma can help in patient stratification and in developing personalized treatment.

Understanding Antidiabetic Potential of Oligosaccharides from Red Alga Dulse Devaleraea inkyuleei Xylan by Investigating α-Amylase and α-Glucosidase Inhibition

In this study, the α-glucosidase (maltase-glucoamylase: MGAM) and α-amylase inhibitory properties elicited by xylooligosaccharides (XOSs) prepared from dulse xylan were analysed as a potential mechanism to control postprandial hyperglycaemia for type-2 diabetes prevention and treatment. Xylan was purified from red alga dulse powder and used for enzymatic hydrolysis using Sucrase X to produce XOSs. Fractionation of XOSs produced xylobiose (X2), β-(1→3)-xylosyl xylobiose (DX3), xylotriose (X3), β-(1→3)-xylosyl-xylotriose (DX4), and a dulse XOS mixture with n ≥ 4 xylose units (DXM). The different fractions exhibited moderate MGAM (IC50 = 11.41-23.44 mg/mL) and α-amylase (IC50 = 18.07-53.04 mg/mL) inhibitory activity, which was lower than that of acarbose. Kinetics studies revealed that XOSs bound to the active site of carbohydrate digestive enzymes, limiting access to the substrate by competitive inhibition. A molecular docking analysis of XOSs with MGAM and α-amylase clearly showed moderate strength of interactions, both hydrogen bonds and non-bonded contacts, at the active site of the enzymes. Overall, XOSs from dulse could prevent postprandial hyperglycaemia as functional food by a usual and continuous consumption.

Metabolism-driven glycosylation represents therapeutic opportunities in interstitial lung diseases

Metabolic changes are coupled with alteration in protein glycosylation. In this review, we will focus on macrophages that are pivotal in the pathogenesis of pulmonary fibrosis and sarcoidosis and thanks to their adaptable metabolism are an attractive therapeutic target. Examples presented in this review demonstrate that protein glycosylation regulates metabolism-driven immune responses in macrophages, with implications for fibrotic processes and granuloma formation. Targeting proteins that regulate glycosylation, such as fucosyltransferases, neuraminidase 1 and chitinase 1 could effectively block immunometabolic changes driving inflammation and fibrosis, providing novel avenues for therapeutic interventions.

Development and application of GlycanDIA workflow for glycomic analysis

Glycans modify protein, lipid, and even RNA molecules to form the regulatory outer coat on cells called the glycocalyx. The changes in glycosylation have been linked to the initiation and progression of many diseases. Thus, while the significance of glycosylation is well established, a lack of accessible methods to characterize glycans has hindered the ability to understand their biological functions. Mass spectrometry (MS)-based methods have generally been at the core of most glycan profiling efforts; however, modern data-independent acquisition (DIA), which could increase sensitivity and simplify workflows, has not been benchmarked for analyzing glycans. Herein, we developed a DIA-based glycomic workflow, termed GlycanDIA, to identify and quantify glycans with high sensitivity and accuracy. The GlycanDIA workflow combined higher energy collisional dissociation (HCD)-MS/MS and staggered windows for glycomic analysis, which facilitates the sensitivity in identification and the accuracy in quantification compared to conventional data-dependent acquisition (DDA)-based glycomics. To facilitate its use, we also developed a generic search engine, GlycanDIA Finder, incorporating an iterative decoy searching for confident glycan identification and quantification from DIA data. The results showed that GlycanDIA can distinguish glycan composition and isomers from N-glycans, O-glycans, and human milk oligosaccharides (HMOs), while it also reveals information on low-abundant modified glycans. With the improved sensitivity, we performed experiments to profile N-glycans from RNA samples, which have been underrepresented due to their low abundance. Using this integrative workflow to unravel the N-glycan profile in cellular and tissue glycoRNA samples, we found that RNA-glycans have specific forms as compared to protein-glycans and are also tissue-specific differences, suggesting distinct functions in biological processes. Overall, GlycanDIA can provide comprehensive information for glycan identification and quantification, enabling researchers to obtain in-depth and refined details on the biological roles of glycosylation.

Two-Dimensional Tandem Mass Spectrometry for Biopolymer Structural Analysis

Biopolymer analysis, including proteomics and glycomics, relies heavily on the use of mass spectrometry for structural elucidation, including sequence determination. Novel methods to improve sample workup, instrument performance, and data analysis continue to be developed to address shortcomings associated with sample preparation, analysis time, data quality, and data interpretation. Here, we present a new method that couples in-source collision-induced dissociation (IS-CID) with two-dimensional tandem mass spectrometry (2D MS/MS) as a way to simplify proteomics and glycomics workflows while also providing additional insight into analyte structures over traditional MS/MS experiments. Specifically, IS-CID is employed as a gas-phase digestion method, i.e., to break down intact full-length polysaccharide or peptide ions prior to mass analysis. The resulting mixtures of oligomeric ions are analyzed by 2D-MS/MS, a technique that allows association of product ions with their precursor ions without isolation of the latter. A novel data analysis strategy is introduced to leverage the second dimension of 2D MS/MS spectra, in which stairstep patterns, representing outputs of a molecule's MSn scans, are extracted for structural interconnectivity information on the oligomer. The results demonstrate the potential applicability of 2D MS/MS strategies to the modern omics workflow and structural analysis of various classes of biopolymers.

A novel family of sugar-specific phosphodiesterases that remove zwitterionic modifications of GlcNAc

The zwitterions phosphorylcholine (PC) and phosphoethanolamine (PE) are often found esterified to certain sugars in polysaccharides and glycoconjugates in a wide range of biological species. One such modification involves PC attachment to the 6-carbon of N-acetylglucosamine (GlcNAc-6-PC) in N-glycans and glycosphingolipids (GSLs) of parasitic nematodes, a modification that helps the parasite evade host immunity. Knowledge of enzymes involved in the synthesis and degradation of PC and PE modifications is limited. More detailed studies on such enzymes would contribute to a better understanding of the function of PC modifications and have potential application in the structural analysis of zwitterion-modified glycans. In this study, we used functional metagenomic screening to identify phosphodiesterases encoded in a human fecal DNA fosmid library that remove PC from GlcNAc-6-PC. A novel bacterial phosphodiesterase was identified and biochemically characterized. This enzyme (termed GlcNAc-PDase) shows remarkable substrate preference for GlcNAc-6-PC and GlcNAc-6-PE, with little or no activity on other zwitterion-modified hexoses. The identified GlcNAc-PDase protein sequence is a member of the large endonuclease/exonuclease/phosphatase superfamily where it defines a distinct subfamily of related sequences of previously unknown function, mostly from Clostridium bacteria species. Finally, we demonstrate use of GlcNAc-PDase to confirm the presence of GlcNAc-6-PC in N-glycans and GSLs of the parasitic nematode Brugia malayi in a glycoanalytical workflow.

NMR chemical shift prediction and structural elucidation of linker-containing oligo- and polysaccharides using the computer program CASPER

Carbohydrate structures containing alkyl groups as aglycones are useful for investigating enzyme activity and glycan-protein interactions. Moreover, linker-containing oligosaccharides with a spacer group are commonly used to print glycan microarrays or to prepare protein-conjugates as vaccine candidates. The structural accuracy of these synthesized glycans are essential for interpretation of results from biological experiments in which the compounds have been used and NMR spectroscopy can unravel and confirm their structures. An approach for efficient 1H and 13C NMR chemical shift assignments employed a parallel NOAH-10 measurement followed by NMR spin-simulation to refine the 1H NMR chemical shifts, as exemplified for a disaccharide with an azidoethyl group as an aglycone, the NMR chemical shifts of which have been used to enhance the quality of CASPER (http://www.casper.organ.su.se/casper/). The CASPER program has been further developed to aid characterization of linker-containing oligo- and polysaccharides, either by chemical shift prediction for comparison to experimental NMR data or as structural investigation of synthesized glycans based on acquired unassigned NMR data. The ability of CASPER to elucidate structures of linker-containing oligosaccharides is demonstrated and comparisons to assigned or unassigned NMR data show the utility of CASPER in supporting a proposed oligosaccharide structure. Prediction of NMR chemical shifts of an oligosaccharide, corresponding to the repeating unit of an O-antigen polysaccharide, having a linker as an aglycone and a non-natural substituent derivative thereof are presented to exemplify the diversity of structures handled. Furthermore, NMR chemical shift predictions of synthesized polysaccharides, corresponding to bacterial polysaccharides, containing a linker are described showing that in addition to oligosaccharide structures also polysaccharide structures having an aglycone spacer group can be analyzed by CASPER.

Diamino Allose Phosphates: Novel, Potent, and Highly Stable Toll-like Receptor 4 Agonists

Most known synthetic toll-like receptor 4 (TLR4) agonists are carbohydrate-based lipid-A mimetics containing several fatty acyl chains, including a labile 3-O-acyl chain linked to the C-3 position of the non-reducing sugar known to undergo cleavage impacting stability and resulting in loss of activity. To overcome this inherent instability, we rationally designed a new class of chemically more stable synthetic TLR4 ligands that elicit robust innate and adaptive immune responses. This new class utilized a diamino allose phosphate (DAP) scaffold containing a nonhydrolyzable 3-amide bond instead of the classical 3-ester. Accordingly, the DAPs have significantly improved thermostability in aqueous formulations and potency relative to other known natural and synthetic TLR4 ligands. Furthermore, the DAP analogues function as potent vaccine adjuvants to enhance influenza-specific antibodies in mice and provide protection against lethal influenza virus challenges. This novel set of TLR4 ligands show promise as next-generation vaccine adjuvants and stand-alone immunomodulators.

Carbohydrate sulfotransferases: a review of emerging diagnostic and prognostic applications

Carbohydrate sulfotransferases (CHST) catalyse the biosynthesis of proteoglycans that enable physical interactions and signalling between different neighbouring cells in physiological and pathological states. The study aim was to provide an overview of emerging diagnostic and prognostic applications of CHST. PubMed database search was conducted using the keywords "carbohydrate sulfotransferase" together with appropriate inclusion and exclusion criteria, whereby 41 publications were selected. Additionally, 40 records on CHST genetic and biochemical properties were hand-picked from UniProt, GeneCards, InterPro, and neXtProt databases. Carbohydrate sulfotransferases have been applied mainly in diagnostics of connective tissue disorders, cancer and inflammations. The lack of CHST activity was found in congenital connective tissue disorders while CHST overexpression was detected in different malignancies. Mutations of CHST3 gene cause skeletal dysplasia, chondrodysplasia, and autosomal recessive multiple joint dislocations while increased tissue expression of CHST11, CHST12 and CHST15 is an unfavourable prognostic factor in ovarian cancer, glioblastoma and pancreatic cancer, respectively. Recently, CHST11 and CHST15 overexpression in the vascular smooth muscle cells was linked to the severe lung pathology in COVID-19 patients. Promising CHST diagnostic and prognostic applications have been described but larger clinical studies and robust analytical procedures are required for the more reliable diagnostic performance estimations.

Characterization of a new family of 6-sulfo-N-acetylglucosaminidases

Sulfation is widespread in nature and plays an important role in modulating biological function. Among the strategies developed by microbes to access sulfated oligosaccharides as a nutrient source is the production of 6-sulfoGlcNAcases to selectively release 6-sulfoGlcNAc from target oligosaccharides. Thus far, all 6-sulfoGlcNAcases identified have belonged to the large GH20 family of β-hexosaminidases. Ηere, we identify and characterize a new, highly specific non-GH20 6-sulfoGlcNAcase from Streptococcus pneumoniae TIGR4, Sp_0475 with a greater than 110,000-fold preference toward N-acetyl-β-D-glucosamine-6-sulfate substrates over the nonsulfated version. Sp_0475 shares distant sequence homology with enzymes of GH20 and with the newly formed GH163 family. However, the sequence similarity between them is sufficiently low that Sp_0475 has been assigned as the founding member of a new glycoside hydrolase family, GH185. By combining results from site-directed mutagenesis with mechanistic studies and bioinformatics we provide insight into the substrate specificity, mechanism, and key active site residues of Sp_0475. Enzymes of the GH185 family follow a substrate-assisted mechanism, consistent with their distant homology to the GH20 family, but the catalytic residues involved are quite different. Taken together, our results highlight in more detail how microbes can degrade sulfated oligosaccharides for nutrients.

Mapping the Acetylamino and Carboxyl Groups on Glycans by Engineered α-Hemolysin Nanopores

Glycan is a crucial class of biological macromolecules with important biological functions. Functional groups determine the chemical properties of glycans, which further affect their biological activities. However, the structural complexity of glycans has set a technical hurdle for their direct identification. Nanopores have emerged as highly sensitive biosensors that are capable of detecting and characterizing various analytes. Here, we identified the functional groups on glycans with a designed α-hemolysin nanopore containing arginine mutations (M113R), which is specifically sensitive to glycans with acetamido and carboxyl groups. Molecular dynamics simulations indicated that the acetamido and carboxyl groups of the glycans produce unique electrical signatures by forming polar and electrostatic interactions with the M113R nanopores. Using these electrical features as the fingerprints, we mapped the length of the glycans containing acetamido and carboxyl groups at the monosaccharide, disaccharide, and trisaccharide levels. This proof-of-concept study provides a promising foundation for developing single-molecule glycan fingerprinting libraries and demonstrates the capability of biological nanopores in glycan sequencing.

Sequence variety in the CC' loop of Siglec-8/9/3 determines the recognitions to sulfated oligosaccharides

Siglecs are important lectins found in different types of immune cells and function as regulatory molecules by recognizing self-associated glycans and converting extracellular interactions into signals for inhibiting immune cell functions. Although many Siglecs have been found to show broad specificities and recognize different types of sulfated oligosaccharides, Siglec-8 and Siglec-9 displayed a high degree of specificity for sialyl N-acetyllactosamine (sLacNAc) with sulfations at O6-positions of the galactose (6'-sulfation) and N-acetylglucosamine (6-sulfation), respectively. Siglec-3 was recently discovered to bind sLacNAc both sulfations. In addition to a conserved arginine residue for binding to sialic acid residue, the sequence variety in the CC' loop may provide binding specificities to sulfated oligosaccharides in Siglecs. Thus, the present study employed molecular models to study the impact of different residues in the CC' loops of Siglec-8/9/3 to the recognitions of 6-sulfations in Gal and/or GlcNAc of sLacNAc. The negatively charged residues in the CC' loop of Siglec-9 formed unfavorable electrostatic repulsions with the 6-sulfate in Gal and resulted no recognitions, in contrast to the favorable interactions formed between the positively charged residues in the CC' loop of Siglec-8 and the 6-sulfate in Gal resulting strong specificity. A two-state binding model was proposed for Siglec-3 recognizing 6-sulfations in Gal and GlcNAc of sLacNAc, as the neutral residues in the CC' loop of Siglec-3 could not form strong favorable interactions to lock the 6-sulfate in Gal within a single binding pose or strong unfavorable interactions to repel the 6-sulfate in Gal. The oligosaccharide adopted two distinctive binding poses and oriented the sulfate groups to form interactions with residues in the CC' loop and G-strand. The present study provided a structural mechanism for the sequence variety in the CC' loop of Siglec-8/9/3 determining the recognitions to the sulfated oligosaccharides and offered insights into the binding specificities for Siglecs.

Role of human milk oligosaccharide metabolizing bacteria in the development of atopic dermatitis/eczema

Despite affecting up to 20% of infants in the United States, there is no cure for atopic dermatitis (AD), also known as eczema. Atopy usually manifests during the first six months of an infant's life and is one predictor of later allergic health problems. A diet of human milk may offer protection against developing atopic dermatitis. One milk component, human milk oligosaccharides (HMOs), plays an important role as a prebiotic in establishing the infant gut microbiome and has immunomodulatory effects on the infant immune system. The purpose of this review is to summarize the available information about bacterial members of the intestinal microbiota capable of metabolizing HMOs, the bacterial genes or metabolic products present in the intestinal tract during early life, and the relationship of these genes and metabolic products to the development of AD/eczema in infants. We find that specific HMO metabolism gene sets and the metabolites produced by HMO metabolizing bacteria may enable the protective role of human milk against the development of atopy because of interactions with the immune system. We also identify areas for additional research to further elucidate the relationship between the human milk metabolizing bacteria and atopy. Detailed metagenomic studies of the infant gut microbiota and its associated metabolomes are essential for characterizing the potential impact of human milk-feeding on the development of atopic dermatitis.

Identification of an energy metabolism-related six-gene signature for distinguishing and forecasting the prognosis of low-grade gliomas

Background

Low-grade gliomas (LGG) account for 20-25% of all gliomas. In this study, we assessed whether metabolic status was correlated with clinical outcomes in LGG patients using data from The Cancer Genome Atlas (TCGA).

Methods

LGG patient data were collected from TCGA, and the Molecular Signature Database was used to extract gene sets related to energy metabolism. After performing a consensus-clustering algorithm, the LGG patients were divided into four clusters. We then compared the tumor prognosis, function, immune cell infiltration, checkpoint proteins, chemo-resistance, and cancer stem cells (CSC) between the two groups with the greatest prognostic difference. Using least absolute shrinkage and selection operator (LASSO) analysis, an energy metabolism-related signature was further developed.

Results

Energy metabolism-related signatures were applied to identify four clusters (C1, C2, C3, and C4) using a consensus-clustering algorithm. C1 LGG patients were more related to the synapse and had higher CSC scores, more chemo-resistance, and a better prognosis. C4 LGG was observed to have more immune-related pathways and better immunity. We then identified six energy metabolism-related genes (PYGL, HS3ST3B, NNMT, FMOD, CHST6, and B3GNT7) that can accurately predict LGG prognosis not only as a whole but also based on the independent predictions of each of these six genes.

Conclusions

The energy metabolism-related subtypes of LGG were identified, which were strongly related to the immune microenvironment, immune checkpoint proteins, CSCs, chemo-resistance, prognosis, and LGG advancement. A signature of genes involved in energy metabolism could help to distinguish and predict the prognosis of LGG patients, and a promising method to discover patients that may benefit from LGG therapy.

Primary Structure of Glycans by NMR Spectroscopy

Glycans, carbohydrate molecules in the realm of biology, are present as biomedically important glycoconjugates and a characteristic aspect is that their structures in many instances are branched. In determining the primary structure of a glycan, the sugar components including the absolute configuration and ring form, anomeric configuration, linkage(s), sequence, and substituents should be elucidated. Solution state NMR spectroscopy offers a unique opportunity to resolve all these aspects at atomic resolution. During the last two decades, advancement of both NMR experiments and spectrometer hardware have made it possible to unravel carbohydrate structure more efficiently. These developments applicable to glycans include, inter alia, NMR experiments that reduce spectral overlap, use selective excitations, record tilted projections of multidimensional spectra, acquire spectra by multiple receivers, utilize polarization by fast-pulsing techniques, concatenate pulse-sequence modules to acquire several spectra in a single measurement, acquire pure shift correlated spectra devoid of scalar couplings, employ stable isotope labeling to efficiently obtain homo- and/or heteronuclear correlations, as well as those that rely on dipolar cross-correlated interactions for sequential information. Refined computer programs for NMR spin simulation and chemical shift prediction aid the structural elucidation of glycans, which are notorious for their limited spectral dispersion. Hardware developments include cryogenically cold probes and dynamic nuclear polarization techniques, both resulting in enhanced sensitivity as well as ultrahigh field NMR spectrometers with a 1H NMR resonance frequency higher than 1 GHz, thus improving resolution of resonances. Taken together, the developments have made and will in the future make it possible to elucidate carbohydrate structure in great detail, thereby forming the basis for understanding of how glycans interact with other molecules.

Computationally guided conversion of the specificity of E-selectin to mimic that of Siglec-8

Sulfated glycans have been found to be associated with various diseases and therefore have significant potential in molecular pathology as biomarkers. Although lectins are useful reagents for detecting glycans, there is a paucity of sulfate-recognizing lectins, and those that exist, such as from Maackia amurensis, display mixed specificities. Recombinant lectin engineering offers an emerging tool for creating novel glycan recognition by altering and/or enhancing endogenous specificities. The present study demonstrated the use of computational approaches in the engineering of a mutated form of E-selectin that displayed highly specific recognition of 6'-sulfo-sialyl Lewis X (6'-sulfo-sLe^x), with negligible binding to its endogenous nonsulfated ligand, sLe^x. This new specificity mimics that of the unrelated protein Siglec-8, for which 6'-sulfo-sLe^x is its preferred ligand. Molecular dynamics simulations and energy calculations predicted that two point mutations (E92A/E107A) would be required to stabilize binding to the sulfated oligosaccharide with E-selectin. In addition to eliminating putative repulsions between the negatively charged side chains and the sulfate moiety, the mutations also abolished favorable interactions with the endogenous ligand. Glycan microarray screening of the recombinantly expressed proteins confirmed the predicted specificity change but also identified the introduction of unexpected affinity for the unfucosylated form of 6'-sulfo-sLe^x (6'-sulfo-sLacNAc). Three key requirements were demonstrated in this case for engineering specificity for sulfated oligosaccharide: 1) removal of unfavorable interactions with the 6'-sulfate, 2) introduction of favorable interactions for the sulfate, and 3) removal of favorable interactions with the endogenous ligand.

The SGNH hydrolase family: a template for carbohydrate diversity

The substitution and de-substitution of carbohydrate materials are important steps in the biosynthesis and/or breakdown of a wide variety of biologically important polymers. The SGNH hydrolase superfamily is a group of related and well-studied proteins with a highly conserved catalytic fold and mechanism composed of 16 member families. SGNH hydrolases can be found in vertebrates, plants, fungi, bacteria, and archaea, and play a variety of important biological roles related to biomass conversion, pathogenesis, and cell signaling. The SGNH hydrolase superfamily is chiefly composed of a diverse range of carbohydrate-modifying enzymes, including but not limited to the carbohydrate esterase families 2, 3, 6, 12 and 17 under the carbohydrate-active enzyme classification system and database (CAZy.org). In this review, we summarize the structural and functional features that delineate these subfamilies of SGNH hydrolases, and which generate the wide variety of substrate preferences and enzymatic activities observed of these proteins to date.

Bioactive polysaccharides and oligosaccharides from garlic (Allium sativum L.): Production, physicochemical and biological properties, and structure-function relationships

Garlic is a common food, and many of its biological functions are attributed to its components including functional carbohydrates. Garlic polysaccharides and oligosaccharides as main components are understudied but have future value due to the growing demand for bioactive polysaccharides/oligosaccharides from natural sources. Garlic polysaccharides have molecular weights of 1 × 10³ to 2 × 10⁶  Da, containing small amounts of pectins and fructooligosaccharides and large amounts of inulin-type fructans ((2→1)-linked β-d-Fruf backbones alone or with attached (2→6)-linked β-d-Fruf branched chains). This article provides a detailed review of research progress and identifies knowledge gaps in extraction, production, composition, molecular characteristics, structural features, physicochemical properties, bioactivities, and structure-function relationships of garlic polysaccharides/oligosaccharides. Whether the extraction processes, synthesis approaches, and modification methods established for other non-garlic polysaccharides are also effective for garlic polysaccharides/oligosaccharides (to preserve their desired molecular structures and bioactivities) requires verification. The metabolic processes of ingested garlic polysaccharides/oligosaccharides (as food ingredients/dietary supplements), their modes of action in healthy humans or populations with chronic conditions, and molecular/chain organization-bioactivity relationships remain unclear. Future research directions related to garlic polysaccharides/oligosaccharides are discussed.

Glyco-nanotechnology: A biomedical perspective

Glycans govern cellular signaling through glycan-protein and glycan-glycan crosstalk. Disruption in the crosstalk initiates 'rogue' signaling and pathology. Nanomaterials supply platforms for multivalent displays of glycans, mediate 'rogue' signal correction, and provide disease treatment modalities (therapeutics). The decorated glycans also target overexpressed lectins on unhealthy cells and direct metal nanoparticles such as gold, iron oxide, and quantum dots to the site of infection. The nanoparticles inform us about the state of the disease (diagnosis) through their distinct optical, magnetic, and electronic properties. Glyco-nanoparticles can sense disease biomarkers, report changes in protein-glycan interactions, and safeguard quality control (analysis). Here we review the current state of glyco-nanotechnology focusing on diagnosis, therapeutics, and analysis of human diseases. We highlight how glyco-nanotechnology could aid in improving diagnostic methods for the detection of disease biomarkers with magnetic resonance imaging (MRI) and fluorescence imaging (FLI), enhance therapeutics such as anti-adhesive treatment of cancer and vaccines against pneumonia, and advance analysis such as the rapid detection of pharmaceutical heparin contaminant and recombinant SARS-COV-2 spike protein. We illustrate these progressions and outline future potentials of glyco-nanotechnology in advancing human health.

Carrageenan From Kappaphycus alvarezii (Rhodophyta, Solieriaceae): Metabolism, Structure, Production, and Application

Carrageenan is a polysaccharide derived from red algae (seaweed) with enormous economic potential in a wide range of industries, including pharmaceuticals, food, cosmetics, printing, and textiles. Carrageenan is primarily produced through aquaculture-based seaweed farming, with Eucheuma and Kappaphycus species accounting for more than 90% of global output. There are three major types of carrageenan found in red algae: kappa (κ)-, iota (ι)-, and lambda (λ)-carrageenan. Kappaphycus alvarezii is the most common kappa-carrageenan source, and it is primarily farmed in Asian countries such as Indonesia, the Philippines, Vietnam, and Malaysia. Carrageenan extracted from K. alvarezii has recently received a lot of attention due to its economic potential in a wide range of applications. This review will discuss K. alvarezii carrageenan in terms of metabolic and physicochemical structure, extraction methods and factors affecting production yield, as well as current and future applications.

The barrier and beyond: Roles of intestinal mucus and mucin-type O-glycosylation in resistance and tolerance defense strategies guiding host-microbe symbiosis

Over the past two decades, our appreciation of the gut mucus has moved from a static lubricant to a dynamic and essential component of the gut ecosystem that not only mediates the interface between host tissues and vast microbiota, but regulates how this ecosystem functions to promote mutualistic symbioses and protect from microbe-driven diseases. By delving into the complex chemistry and biology of the mucus, combined with innovative in vivo and ex vivo approaches, recent studies have revealed novel insights into the formation and function of the mucus system, the O-glycans that make up this system, and how they mediate two major host-defense strategies - resistance and tolerance - to reduce damage caused by indigenous microbes and opportunistic pathogens. This current review summarizes these findings by highlighting the emerging roles of mucus and mucin-type O-glycans in influencing host and microbial physiology with an emphasis on host defense strategies against bacteria in the gastrointestinal tract.

Glyco-Decipher enables glycan database-independent peptide matching and in-depth characterization of site-specific N-glycosylation

Glycopeptides with unusual glycans or poor peptide backbone fragmentation in tandem mass spectrometry are unaccounted for in typical site-specific glycoproteomics analysis and thus remain unidentified. Here, we develop a glycoproteomics tool, Glyco-Decipher, to address these issues. Glyco-Decipher conducts glycan database-independent peptide matching and exploits the fragmentation pattern of shared peptide backbones in glycopeptides to improve the spectrum interpretation. We benchmark Glyco-Decipher on several large-scale datasets, demonstrating that it identifies more peptide-spectrum matches than Byonic, MSFragger-Glyco, StrucGP and pGlyco 3.0, with a 33.5%-178.5% increase in the number of identified glycopeptide spectra. The database-independent and unbiased profiling of attached glycans enables the discovery of 164 modified glycans in mouse tissues, including glycans with chemical or biological modifications. By enabling in-depth characterization of site-specific protein glycosylation, Glyco-Decipher is a promising tool for advancing glycoproteomics analysis in biological research.

Small molecule inhibitors of mammalian glycosylation

Glycans are one of the fundamental biopolymers encountered in living systems. Compared to polynucleotide and polypeptide biosynthesis, polysaccharide biosynthesis is a uniquely combinatorial process to which interdependent enzymes with seemingly broad specificities contribute. The resulting intracellular cell surface, and secreted glycans play key roles in health and disease, from embryogenesis to cancer progression. The study and modulation of glycans in cell and organismal biology is aided by small molecule inhibitors of the enzymes involved in glycan biosynthesis. In this review, we survey the arsenal of currently available inhibitors, focusing on agents which have been independently validated in diverse systems. We highlight the utility of these inhibitors and drawbacks to their use, emphasizing the need for innovation for basic research as well as for therapeutic applications.

Small tools for sweet challenges: advances in microfluidic technologies for glycan synthesis

Glycans, including oligosaccharides and glycoconjugates, play an integral role in modulating the biological functions of macromolecules. Many physiological and pathological processes are mediated by interactions between glycans, which has led to the use of glycans as biosensors for pathogen and biomarker detection. Elucidating the relationship between glycan structure and biological function is critical for advancing our understanding of the impact glycans have on human health and disease and for expanding the repertoire of glycans available for bioanalysis, especially for diagnostics. Such efforts have been limited by the difficulty in obtaining sufficient quantities of homogenous glycan samples needed to resolve the exact relationships between glycan structure and their structural or modulatory functions on a given glycoconjugate. Synthetic strategies offer a viable route for overcoming these technical hurdles. In recent years, microfluidics have emerged as powerful tools for realizing high-throughput and reproducible syntheses of homogenous glycans for the potential use in functional studies. This critical review provides readers with an overview of the microfluidic technologies that have been developed for chemical and enzymatic glycan synthesis. The advantages and limitations associated with using microreactor platforms to improve the scalability, productivity, and selectivity of glycosylation reactions will be discussed, as well as suggested future work that can address certain pitfalls.

On resin synthesis of sulfated oligosaccharides

Sulfated glycans are involved in many biological processes, making well-defined sulfated oligosaccharides highly sought molecular probes. These compounds are a considerable synthetic challenge, with each oligosaccharide target requiring specific synthetic protocols and extensive purifications steps. Here, we describe a general on resin approach that simplifies the synthesis of sulfated glycans. The oligosaccharide backbone, obtained by Automated Glycan Assembly (AGA), is subjected to regioselective sulfation and hydrolysis of protecting groups. The protocol is compatible with several monosaccharides and allows for multi-sulfation of linear and branched glycans. Seven diverse, biologically relevant sulfated glycans were prepared in good to excellent overall yield.

Purification, molecular characterization and ligand binding properties of the major donkey seminal plasma protein DSP-1

Fibronectin type-II (FnII) family proteins are the major proteins in many mammalian species including bull, horse and pig. In the present study, a major FnII protein has been identified and isolated from donkey (Equus hemionus) seminal plasma, which we refer to as Donkey Seminal Plasma protein-1 (DSP-1). The amino acid sequence determined by mass spectrometry and computational modeling studies revealed that DSP-1 is homologous to other mammalian seminal plasma proteins, including bovine PDC-109 (also known as BSP-A1/A2) and equine HSP-1/2. High-resolution LC-MS analysis indicated that the protein is heterogeneously glycosylated and also contains multiple acetylations, occurring in the attached glycans. Structural and thermal stability studies on DSP-1 employing CD spectroscopy and differential scanning calorimetry showed that the protein unfolds at ~43 °C and binding to phosphorylcholine (PrC) - the head group moiety of choline phospholipids - increases its thermal stability. Intrinsic fluorescence titrations revealed that DSP-1 recognizes lyso-phosphatidylcholine with over 100-fold higher affinity than PrC. Further, interaction of DSP-1 with erythrocytes, a model cell membrane, revealed that DSP-1 binding is mediated by a specific interaction with choline phospholipids and results in membrane perturbation, suggesting that binding of this protein to sperm plasma membrane could be physiologically significant.

Expedited synthesis of mannose-6-phosphate containing oligosaccharides

Currently, the reaction toolbox for the functionalization of glycans assembled on solid-phase is quite limited. Automated (1 h) and manual (overnight) phosphorylation protocols that enable the solid-phase synthesis of oligosaccharides containing up to two mannose-6-phosphates are presented. Automated glycan assembly expedited access to substrates and facilitated the screening of experimental conditions.

Natural Presentation of Glycosaminoglycans in Synthetic Matrices for 3D Angiogenesis Models

Glycosaminoglycans (GAGs) are long, linear polysaccharides that occur in the extracellular matrix of higher organisms and are either covalently attached to protein cores, as proteoglycans or in free form. Dependent on their chemical composition and structure, GAGs orchestrate a wide range of essential functions in tissue homeostasis. Accordingly, GAG-based biomaterials play a major role in tissue engineering. Current biomaterials exploit crosslinks between chemically modified GAG chains. Due to modifications along the GAG chains, they are limited in their GAG-protein interactions and accessibility to dissect the biochemical and biophysical properties that govern GAG functions. Herein, a natural presentation of GAGs is achieved by a terminal immobilization of GAGs to a polyethylene glycol (PEG) hydrogel. A physicochemical characterization showed that different end-thiolated GAGs can be incorporated within physiological concentration ranges, while the mechanical properties of the hydrogel are exclusively tunable by the PEG polymer concentration. The functional utility of this approach was illustrated in a 3D cell culture application. Immobilization of end-thiolated hyaluronan enhanced the formation of capillary-like sprouts originating from embedded endothelial cell spheroids. Taken together, the presented PEG/GAG hydrogels create a native microenvironment with fine-tunable mechanobiochemical properties and are an effective tool for studying and employing the bioactivity of GAGs.

2-Dimensional ultra-high performance liquid chromatography and DMT-MM derivatization paired with tandem mass spectrometry for comprehensive serum N-glycome characterization

Glycosylation is a prominent co- and post-translational modification which contributes to a variety of important biological functions. Protein glycosylation characteristics, particularly N-glycosylation, are influenced by changes in one's pathological state, such as through the presence of disease, and as such, there is great interest in N-glycans as potential disease biomarkers. Human serum is an attractive source for N-glycan based biomarker studies as circulatory proteins are representative of one's physiology, with many serum proteins containing N-glycosylation. The difficulty in comprehensively characterizing the serum N-glycome arises from the absence of a biosynthetic template resulting in great structural heterogeneity and complexity. To help overcome these challenges we developed a 2-dimensional liquid chromatography platform which utilizes offline weak anion exchange (WAX) chromatography in the first dimension and hydrophilic interaction liquid chromatography (HILIC) in the second dimension to separate N-glycans by charge, corresponding to degree of sialylation, and size, respectively. Performing these separations offline enables subsequent derivatization with 4-(4,6-Dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM) for sialic acid linkage determination and the identification of sialic acid linkage isomers. Subsequent tandem mass spectrometry analysis revealed the identification of 212 complete and partial N-glycan structures including low abundant N-glycans containing acetyl and sulphate modifications. The identifications obtained through this platform were then applied to N-glycans released from a set of stage 3 gastric cancer serum samples obtained from patients before (pre-op) and after (post-op) tumour resection to investigate how the serum N-glycome can facilitate differentiation between the two pathological states.

Combining functional metagenomics and glycoanalytics to identify enzymes that facilitate structural characterization of sulfated N-glycans

BACKGROUND

Sulfate modification of N-glycans is important for several biological functions such as clearance of pituitary hormones or immunoregulation. Yet, the prevalence of this N-glycan modification and its functions remain largely unexplored. Characterization of N-glycans bearing sulfate modifications is hampered in part by a lack of enzymes that enable site-specific detection of N-glycan sulfation. In this study, we used functional metagenomic screening to identify enzymes that act upon sulfated N-acetylglucosamine (GlcNAc). Using multiplexed capillary gel electrophoresis with laser-induced fluorescence detection (xCGE-LIF) -based glycoanalysis we proved their ability to act upon GlcNAc-6-SO4 on N-glycans.

RESULTS

Our screen identified a sugar-specific sulfatase that specifically removes sulfate from GlcNAc-6-SO4 when it is in a terminal position on an N-glycan. Additionally, in the absence of calcium, this sulfatase binds to the sulfated glycan but does not remove the sulfate group, suggesting it could be used for selective isolation of sulfated N-glycans. Further, we describe isolation of a sulfate-dependent hexosaminidase that removes intact GlcNAc-6-SO4 (but not asulfated GlcNAc) from a terminal position on N-glycans. Finally, the use of these enzymes to detect the presence of sulfated N-glycans by xCGE-LIF is demonstrated.

CONCLUSION

The present study demonstrates the feasibility of using functional metagenomic screening combined with glycoanalytics to discover enzymes that act upon chemical modifications of glycans. The discovered enzymes represent new specificities that can help resolve the presence of GlcNAc-6-SO4 in N-glycan structural analyses.

An Integrated Strategy Reveals Complex Glycosylation of Erythropoietin Using Mass Spectrometry

The characterization of therapeutic glycoproteins is challenging due to the structural heterogeneity of the therapeutic protein glycosylation. This study presents an in-depth analytical strategy for glycosylation of first-generation erythropoietin (epoetin beta), including a developed mass spectrometric workflow for N-glycan analysis, bottom-up mass spectrometric methods for site-specific N-glycosylation, and a LC-MS approach for O-glycan identification. Permethylated N-glycans, peptides, and enriched glycopeptides of erythropoietin were analyzed by nanoLC-MS/MS, and de-N-glycosylated erythropoietin was measured by LC-MS, enabling the qualitative and quantitative analysis of glycosylation and different glycan modifications (e.g., phosphorylation and O-acetylation). The newly developed Python scripts enabled the identification of 140 N-glycan compositions (237 N-glycan structures) from erythropoietin, especially including 8 phosphorylated N-glycan species. The site-specificity of N-glycans was revealed at the glycopeptide level by pGlyco software using different proteases. In total, 114 N-glycan compositions were identified from glycopeptide analysis. Moreover, LC-MS analysis of de-N-glycosylated erythropoietin species identified two O-glycan compositions based on the mass shifts between non-O-glycosylated and O-glycosylated species. Finally, this integrated strategy was proved to realize the in-depth glycosylation analysis of a therapeutic glycoprotein to understand its pharmacological properties and improving the manufacturing processes.

Novel lamprey antibody recognizes terminal sulfated galactose epitopes on mammalian glycoproteins

The terminal galactose residues of N- and O-glycans in animal glycoproteins are often sialylated and/or fucosylated, but sulfation, such as 3-O-sulfated galactose (3-O-SGal), represents an additional, but poorly understood modification. To this end, we have developed a novel sea lamprey variable lymphocyte receptor (VLR) termed O6 to explore 3-O-SGal expression. O6 was engineered as a recombinant murine IgG chimera and its specificity and affinity to the 3-O-SGal epitope was defined using a variety of approaches, including glycan and glycoprotein microarray analyses, isothermal calorimetry, ligand-bound crystal structure, FACS, and immunohistochemistry of human tissue macroarrays. 3-O-SGal is expressed on N-glycans of many plasma and tissue glycoproteins, but recognition by O6 is often masked by sialic acid and thus exposed by treatment with neuraminidase. O6 recognizes many human tissues, consistent with expression of the cognate sulfotransferases (GAL3ST-2 and GAL3ST-3). The availability of O6 for exploring 3-O-SGal expression could lead to new biomarkers for disease and aid in understanding the functional roles of terminal modifications of glycans and relationships between terminal sulfation, sialylation and fucosylation.

Chemical Glycosylation and Its Application to Glucose Homeostasis-Regulating Peptides

Peptides and proteins are attractive targets for therapeutic drug development due to their exquisite target specificity and low toxicity profiles. However, their complex structures give rise to several challenges including solubility, stability, aggregation, low bioavailability, and poor pharmacokinetics. Numerous chemical strategies to address these have been developed including the introduction of several natural and non-natural modifications such as glycosylation, lipidation, cyclization and PEGylation. Glycosylation is considered to be one of the most useful modifications as it is known to contribute to increasing the stability, to improve solubility, and increase the circulating half-lifves of these biomolecules. However, cellular glycosylation is a highly complex process that generally results in heterogenous glycan structures which confounds quality control and chemical and biological assays. For this reason, much effort has been expended on the development of chemical methods, including by solid phase peptide synthesis or chemoenzymatic processes, to enable the acquisition of homogenous glycopeptides to greatly expand possibilities in drug development. In this mini-review, we highlight the importance of such chemical glycosylation methods for improving the biophysical properties of naturally non-glycosylated peptides as applied to the therapeutically essential insulin and related peptides that are used in the treatment of diabetes.

Comparative Analysis of Different N-glycan Preparation Approaches and Development of Optimized Solid-Phase Permethylation Using Mass Spectrometry

Protein N-glycosylation characterization is challenging due to structural micro- and macro-heterogeneity. Although various N-glycan preparation strategies, including purification and derivatization, have been previously developed prior to mass spectrometric analysis, systematic evaluation still needs to be performed. This study compared the different N-glycan purification strategies, including filter-aided sample preparation, de-N-glycosylated protein precipitation, and trypsin digestion followed by reversed phase-based solid-phase extraction, and derivatization approaches, such as solid-phase permethylation, reductive amination, and reduction. With the comparative analysis, an optimized solid-phase permethylation (OSPP) workflow was developed for mass spectrometric N-glycomics, showing simplified analysis for N-glycan compositions and high yields using etanercept. The N-glycan samples released from trastuzumab and adalimumab were utilized to test OSPP to obtain their N-glycan profiles using mass spectrometry. Based on different standard procedures across laboratories, this study provides the reference for analysts to select an appropriate N-glycan preparation method with their research purposes.

Sweet systems: technologies for glycomic analysis and their integration into systems biology

Found in virtually every organism, glycans are essential molecules that play important roles in almost every aspect of biology. The composition of glycome, the repertoire of glycans in an organism or a biological sample, is often found altered in many diseases, including cancer, infectious diseases, metabolic and developmental disorders. Understanding how glycosylation and glycomic changes enriches our knowledge of the mechanisms of disease progression and sheds light on the development of novel therapeutics. However, the inherent diversity of glycan structures imposes challenges on the experimental characterization of glycomes. Advances in high-throughput glycomic technologies enable glycomic analysis in a rapid and comprehensive manner. In this review, we discuss the analytical methods currently used in high-throughput glycomics, including mass spectrometry, liquid chromatography and lectin microarray. Concomitant with the technical advances is the integration of glycomics into systems biology in the recent years. Herein we elaborate on some representative works from this recent trend to underline the important role of glycomics in such integrated approaches to disease.

The Tumour Microenvironment and Circulating Tumour Cells: A Partnership Driving Metastasis and Glycan-Based Opportunities for Cancer Control

Circulating tumour cells (CTC) are rare cells that actively detach or are shed from primary tumours into the lymph and blood. Some CTC subpopulations gain the capacity to survive, home and colonize distant locations, forming metastasis. This results from a multifactorial process in which cancer cells optimize motility, invasion, immune escape and cooperative relationships with microenvironmental cues. Here we present evidences of a self-fuelling molecular crosstalk between cancer cells and the tumour stroma supporting the main milestones leading to metastasis. We discuss how the tumour microenvironment supports pre-metastatic niches and CTC development and ultimately dictates CTC fate in targeted organs. Finally, we highlight the key role played by protein glycosylation in metastasis development, its prompt response to microenvironmental stimuli and the tremendous potential of glycan-based molecular signatures for liquid biopsies and targeted therapeutics.

Peak Filtering, Peak Annotation, and Wildcard Search for Glycoproteomics

Glycopeptides in peptide or digested protein samples pose a number of analytical and bioinformatics challenges beyond those posed by unmodified peptides or peptides with smaller posttranslational modifications. Exact structural elucidation of glycans is generally beyond the capability of a single mass spectrometry experiment, so a reasonable level of identification for tandem mass spectrometry, taken by several glycopeptide software tools, is that of peptide sequence and glycan composition, meaning the number of monosaccharides of each distinct mass, e.g., HexNAc(2)Hex(5) rather than man5. Even at this level, however, glycopeptide analysis poses challenges: finding glycopeptide spectra when they are a tiny fraction of the total spectra; assigning spectra with unanticipated glycans, not in the initial glycan database; and finding, scoring, and labeling diagnostic peaks in tandem mass spectra. Here, we discuss recent improvements to Byonic, a glycoproteomics search program, that address these three issues. Byonic now supports filtering spectra by m/z peaks, so that the user can limit attention to spectra with diagnostic peaks, e.g., at least two out of three of 204.087 for HexNAc, 274.092 for NeuAc (with water loss), and 366.139 for HexNAc-Hex, all within a set mass tolerance, e.g., ± 0.01 Da. Also, new is glycan "wildcard" search, which allows an unspecified mass within a user-set mass range to be applied to N- or O-linked glycans and enables assignment of spectra with unanticipated glycans. Finally, the next release of Byonic supports user-specified peak annotations from user-defined posttranslational modifications. We demonstrate the utility of these new software features by finding previously unrecognized glycopeptides in publicly available data, including glycosylated neuropeptides from rat brain.

Advances in the Chemical Synthesis of Carbohydrates and Glycoconjugates

Carbohydrates are functional and structural biomolecules with structures ranging from monosaccharides to polysaccharides. They are naturally found as pure glycans or attached to lipids and proteins forming glycoconjugates. The biosynthesis of carbohydrates is not genetically controlled. The regulation takes place by the expression of enzymes that transfer and hydrolyze the glycan units, leading to glycocojugates having complex mixtures of glycan structures. Chemical synthesis emerged as the best strategy to obtain defined glycan and glycoconjugates and overcome the challenging purification processes. Here, we review the recent advances in the synthesis of oligosaccharides using manual and automated methods. The chapter covers the methods for the preparation of building blocks and control of stereoselectivity and regioselectivity during glycosylations. Finally, it also presents the strategies to obtain natural and non-natural glycoconjugates with lipids and proteins.

Decorating the Anammox House: Sialic Acids and Sulfated Glycosaminoglycans in the Extracellular Polymeric Substances of Anammox Granular Sludge

Anammox (anaerobic ammonium oxidation) bacteria are important for the nitrogen cycle in both natural environments and wastewater treatment plants. These bacteria have a strong tendency to grow in aggregates like biofilms and granular sludge. To understand the formation of anammox aggregates, it is required to unravel the composition of the extracellular polymeric substances (EPS), which are produced by the bacteria to develop into aggregates and granules. Here, we investigated anionic polymers in anammox granular sludge, focussing on sialic acids and sulfated glycosaminoglycans. Quantification assays and fluorescent stains indicated that sialic acids and sulfated glycosaminoglycans were present in the anammox EPS (1.6% equivalents of sialic acids and 2.4% equivalents of sulfated glycosaminoglycans). Additionally, the potential genes for the biosynthesis of sialic acids and sulfated glycosaminoglycans were analyzed in the anammox draft genomes. The finding of these components in anammox granular sludge and previously in other nonpathogenic bacteria pointed out that sialic acids and sulfated glycosaminoglycans are worth investigating in the context of a broader function in microbial communities and biofilm systems in general.