Genetic defects in the human glycome

In vivo mapping of the mouse Galnt3-specific O-glycoproteome

The UDP-N-acetylgalactosamine polypeptide:N-acetylgalactosaminyltransferase (GalNAc-T) family of enzymes initiates O-linked glycosylation by catalyzing the addition of the first GalNAc sugar to serine or threonine on proteins destined to be membrane-bound or secreted. Defects in individual isoforms of the GalNAc-T family can lead to certain congenital disorders of glycosylation (CDG). The polypeptide N-acetylgalactosaminyltransferase 3 (GALNT)3-CDG, is caused by mutations in GALNT3, resulting in hyperphosphatemic familial tumoral calcinosis due to impaired glycosylation of the phosphate-regulating hormone fibroblast growth factor 23 (FGF23) within osteocytes of the bone. Patients with hyperphosphatemia present altered bone density, abnormal tooth structure, and calcified masses throughout the body. It is therefore important to identify all potential substrates of GalNAc-T3 throughout the body to understand the complex disease phenotypes. Here, we compared the Galnt3-/- mouse model, which partially phenocopies GALNT3-CDG, with WT mice and used a multicomponent approach using chemoenzymatic conditions, a product-dependent method constructed using EThcD triggered scans in a mass spectrometry workflow, quantitative O-glycoproteomics, and global proteomics to identify 663 Galnt3-specific O-glycosites from 269 glycoproteins across multiple tissues. Consistent with the mouse and human phenotypes, functional networks of glycoproteins that contain GalNAc-T3-specific O-glycosites involved in skeletal morphology, mineral level maintenance, and hemostasis were identified. This library of in vivo GalNAc-T3-specific substrate proteins and O-glycosites will serve as a valuable resource to understand the functional implications of O-glycosylation and to unravel the underlying causes of complex human GALNT3-CDG phenotypes.

Novel regulatory mechanisms of N-glycan sialylation: Implication of integrin and focal adhesion kinase in the regulation

BACKGROUND

Sialylation of glycoproteins, including integrins, is crucial in various cancers and diseases such as immune disorders. These modifications significantly impact cellular functions and are associated with cancer progression. Sialylation, catalyzed by specific sialyltransferases (STs), has traditionally been considered to be regulated at the mRNA level.

SCOPE OF REVIEW

Recent research has expanded our understanding of sialylation, revealing ST activity changes beyond mRNA level variations. This includes insights into COPI vesicle formation and Golgi apparatus maintenance and identifying specific target proteins of STs that are not predictable through recombinant enzyme assays.

MAJOR CONCLUSIONS

This review summarizes that Golgi-associated pathways largely influence the regulation of STs. GOLPH3, GORAB, PI4K, and FAK have become critical elements in sialylation regulation. Some STs have been revealed to possess specificity for specific target proteins, suggesting the presence of additional, enzyme-specific regulatory mechanisms.

GENERAL SIGNIFICANCE

This study enhances our understanding of the molecular interplay in sialylation regulation, mainly focusing on the role of integrin and FAK. It proposes a bidirectional system where sialylations might influence integrins and vice versa. The diversity of STs and their specific linkages offer new perspectives in cancer research, potentially broadening our understanding of cellular mechanisms and opening avenues for new therapeutic approaches in targeting sialylation pathways.

The Human Blood N-Glycome: Unraveling Disease Glycosylation Patterns

Most of the proteins in the circulation are N-glycosylated, shaping together the total blood N-glycome (TBNG). Glycosylation is known to affect protein function, stability, and clearance. The TBNG is influenced by genetic, environmental, and metabolic factors, in part epigenetically imprinted, and responds to a variety of bioactive signals including cytokines and hormones. Accordingly, physiological and pathological events are reflected in distinct TBNG signatures. Here, we assess the specificity of the emerging disease-associated TBNG signatures with respect to a number of key glycosylation motifs including antennarity, linkage-specific sialylation, fucosylation, as well as expression of complex, hybrid-type and oligomannosidic N-glycans, and show perplexing complexity of the glycomic dimension of the studied diseases. Perspectives are given regarding the protein- and site-specific analysis of N-glycosylation, and the dissection of underlying regulatory layers and functional roles of blood protein N-glycosylation.

Clinical and biochemical footprints of congenital disorders of glycosylation: Proposed nosology

We have identified 200 congenital disorders of glycosylation (CDG) caused by 189 different gene defects and have proposed a classification system for CDG based on the mode of action. This classification includes 8 categories: 1. Disorders of monosaccharide synthesis and interconversion, 2. Disorders of nucleotide sugar synthesis and transport, 3. Disorders of N-linked protein glycosylation, 4. Disorders of O-linked protein glycosylation, 5. Disorders of lipid glycosylation, 6. Disorders of vesicular trafficking, 7. Disorders of multiple glycosylation pathways and 8. Disorders of glycoprotein/glycan degradation. Additionally, using information from IEMbase, we have described the clinical involvement of 19 organs and systems, as well as essential laboratory investigations for each type of CDG. Neurological, dysmorphic, skeletal, and ocular manifestations were the most prevalent, occurring in 81%, 56%, 53%, and 46% of CDG, respectively. This was followed by digestive, cardiovascular, dermatological, endocrine, and hematological symptoms (17-34%). Immunological, genitourinary, respiratory, psychiatric, and renal symptoms were less frequently reported (8-12%), with hair and dental abnormalities present in only 4-7% of CDG. The information provided in this study, including our proposed classification system for CDG, may be beneficial for healthcare providers caring for individuals with metabolic conditions associated with CDG.

Exploring glycans as vital biological macromolecules: A comprehensive review of advancements in biomedical frontiers

This comprehensive review delves into the intricate landscape of glycans and glycoconjugates, unraveling their multifaceted roles across diverse biological dimensions. From influencing fundamental cellular processes such as signaling, recognition, and adhesion to exerting profound effects at the molecular and genetic levels, these complex carbohydrate structures emerge as linchpins in cellular functions and interactions. The structural diversity of glycoconjugates, which can be specifically classified into glycoproteins, glycolipids, and proteoglycans, underscores their importance in shaping the architecture of cells. Beyond their structural roles, these molecules also play key functions in facilitating cellular communication and modulating recognition mechanisms. Further, glycans and glycoconjugates prove invaluable as biomarkers in disease diagnostics, particularly in cancer, where aberrant glycosylation patterns offer critical diagnostic cues. Furthermore, the review explores their promising therapeutic applications, ranging from the development of glycan-based nanomaterials for precise drug delivery to innovative interventions in cancer treatment. This review endeavors to comprehensively explore the intricate functions of glycans and glycoconjugates, with the primary goal of offering valuable insights into their extensive implications in both health and disease. Encompassing a broad spectrum of biological processes, the focus of the review aims to provide a comprehensive understanding of the significant roles played by glycans and glycoconjugates.

Liquid Biomarkers in Prostate Cancer Diagnosis: Current Status and Emerging Prospects

Prostate cancer (PCa) is a major health concern that necessitates appropriate diagnostic approaches for timely intervention. This review critically evaluates the role of liquid biopsy techniques, focusing on blood- and urine-based biomarkers, in overcoming the limitations of conventional diagnostic methods. The 4Kscore test and Prostate Health Index have demonstrated efficacy in distinguishing PCa from benign conditions. Urinary biomarker tests such as PCa antigen 3, MyProstateScore, SelectMDx, and ExoDx Prostate IntelliScore test have revolutionized risk stratification and minimized unnecessary biopsies. Emerging biomarkers, including non-coding RNAs, circulating tumor DNA, and prostate-specific antigen (PSA) glycosylation, offer valuable insights into PCa biology, enabling personalized treatment strategies. Advancements in non-invasive liquid biomarkers for PCa diagnosis may facilitate the stratification of patients and avoid unnecessary biopsies, particularly when PSA is in the gray area of 4 to 10 ng/mL.

Mannose: A Promising Player in Clinical and Biomedical Applications

Mannose, an isomer of glucose, exhibits a distinct molecular structure with the same formula but a different atom arrangement, contributing to its specific biological functions. Widely distributed in body fluids and tissues, particularly in the nervous system, skin, testes, and retinas, mannose plays a crucial role as a direct precursor for glycoprotein synthesis. Glycoproteins, essential for immune regulation and glycosylation processes, underscore the significance of mannose in these physiological activities. The clinical and biomedical applications of mannose are diverse, encompassing its anti-inflammatory properties, potential to inhibit bacterial infections, role in metabolism regulation, and suggested involvement in alleviating diabetes and obesity. Additionally, mannose shows promise in antitumor effects, immune modulation, and the construction of drug carriers, indicating a broad spectrum of therapeutic potential. The article aims to present a comprehensive review of mannose, focusing on its molecular structure, metabolic pathways, and clinical and biomedical applications, and also to emphasize its status as a promising therapeutic agent.

Golgi Apparatus Target Proteins in Gastroenterological Cancers: A Comprehensive Review of GOLPH3 and GOLGA Proteins

The Golgi apparatus plays a central role in protein sorting, modification and trafficking within cells; its dysregulation has been implicated in various cancers including those affecting the GI tract. This review highlights two Golgi target proteins, namely GOLPH3 and GOLGA proteins, from this apparatus as they relate to gastroenterological cancers. GOLPH3-a highly conserved protein of the trans-Golgi network-has become a key player in cancer biology. Abnormal expression of GOLPH3 has been detected in various gastrointestinal cancers including gastric, colorectal and pancreatic cancers. GOLPH3 promotes tumor cell proliferation, survival, migration and invasion via various mechanisms including activating the PI3K/Akt/mTOR signaling pathway as well as altering Golgi morphology and vesicular trafficking. GOLGA family proteins such as GOLGA1 (golgin-97) and GOLGA7 (golgin-84) have also been implicated in gastroenterological cancers. GOLGA1 plays an essential role in protein trafficking within the Golgi apparatus and has been associated with poor patient survival rates and increased invasiveness; GOLGA7 maintains Golgi structure while having been shown to affect protein glycosylation processes. GOLPH3 and GOLGA proteins play a pivotal role in gastroenterological cancer, helping researchers unlock molecular mechanisms and identify therapeutic targets. Their dysregulation affects various cellular processes including signal transduction, vesicular trafficking and protein glycosylation, all contributing to tumor aggressiveness and progression.

Glycosylation and behavioral symptoms in neurological disorders

Glycosylation, the addition of glycans or carbohydrates to proteins, lipids, or other glycans, is a complex post-translational modification that plays a crucial role in cellular function. It is estimated that at least half of all mammalian proteins undergo glycosylation, underscoring its importance in the functioning of cells. This is reflected in the fact that a significant portion of the human genome, around 2%, is devoted to encoding enzymes involved in glycosylation. Changes in glycosylation have been linked to various neurological disorders, including Alzheimer's disease, Parkinson's disease, autism spectrum disorder, and schizophrenia. Despite its widespread occurrence, the role of glycosylation in the central nervous system remains largely unknown, particularly with regard to its impact on behavioral abnormalities in brain diseases. This review focuses on examining the role of three types of glycosylation: N-glycosylation, O-glycosylation, and O-GlcNAcylation, in the manifestation of behavioral and neurological symptoms in neurodevelopmental, neurodegenerative, and neuropsychiatric disorders.

The Association of the Polymorphisms in the FUT8-Related Locus with the Plasma Glycosylation in Post-Traumatic Stress Disorder

The molecular underpinnings of post-traumatic stress disorder (PTSD) are still unclear due to the complex interactions of genetic, psychological, and environmental factors. Glycosylation is a common post-translational modification of proteins, and different pathophysiological states, such as inflammation, autoimmune diseases, and mental disorders including PTSD, show altered N-glycome. Fucosyltransferase 8 (FUT8) is the enzyme that catalyzes the addition of core fucose on glycoproteins, and mutations in the FUT8 gene are associated with defects in glycosylation and functional abnormalities. This is the first study that investigated the associations of plasma N-glycan levels with FUT8-related rs6573604, rs11621121, rs10483776, and rs4073416 polymorphisms and their haplotypes in 541 PTSD patients and control participants. The results demonstrated that the rs6573604 T allele was more frequent in the PTSD than in the control participants. Significant associations of plasma N-glycan levels with PTSD and FUT8-related polymorphisms were observed. We also detected associations of rs11621121 and rs10483776 polymorphisms and their haplotypes with plasma levels of specific N-glycan species in both the control and PTSD groups. In carriers of different rs6573604 and rs4073416 genotypes and alleles, differences in plasma N-glycan levels were only found in the control group. These molecular findings suggest a possible regulatory role of FUT8-related polymorphisms in glycosylation, the alternations of which could partially explain the development and clinical manifestation of PTSD.

Heritability of the glycan clock of biological age

Immunoglobulin G is posttranslationally modified by the addition of complex N-glycans affecting its function and mediating inflammation at multiple levels. IgG glycome composition changes with age and health in a predictive pattern, presumably due to inflammaging. As a result, a novel biological aging biomarker, glycan clock of age, was developed. Glycan clock of age is the first of biological aging clocks for which multiple studies showed a possibility of clock reversal even with simple lifestyle interventions. However, none of the previous studies determined to which extent the glycan clock can be turned, and how much is fixed by genetic predisposition. To determine the contribution of genetic and environmental factors to phenotypic variation of the glycan clock, we performed heritability analysis on two TwinsUK female cohorts. IgG glycans from monozygotic and dizygotic twin pairs were analyzed by UHPLC and glycan age was calculated using the glycan clock. In order to determine additive genetic, shared, and unique environmental contributions, a classical twin design was applied. Heritability of the glycan clock was calculated for participants of one cross-sectional and one longitudinal cohort with three time points to assess the reliability of measurements. Heritability estimate for the glycan clock was 39% on average, suggesting a moderate contribution of additive genetic factors (A) to glycan clock variation. Remarkably, heritability estimates remained approximately the same in all time points of the longitudinal study, even though IgG glycome composition changed substantially. Most environmental contributions came from shared environmental factors (C), with unique environmental factors (E) having a minor role. Interestingly, heritability estimates nearly doubled, to an average of 71%, when we included age as a covariant. This intervention also inflated the estimates of unique environmental factors contributing to glycan clock variation. A complex interplay between genetic and environmental factors defines alternative IgG glycosylation during aging and, consequently, dictates the glycan clock's ticking. Apparently, environmental factors (including lifestyle choices) have a strong impact on the biological age measured with the glycan clock, which additionally clarifies why this aging clock is one of the most potent biomarkers of biological aging.

Immunoglobulin G N-Glycosylation Signatures in Incident Type 2 Diabetes and Cardiovascular Disease

OBJECTIVE

N-glycosylation is a functional posttranslational modification of immunoglobulins (Igs). We hypothesized that specific IgG N-glycans are associated with incident type 2 diabetes and cardiovascular disease (CVD).

RESEARCH DESIGN AND METHODS

We performed case-cohort studies within the population-based European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam cohort (2,127 in the type 2 diabetes subcohort [741 incident cases]; 2,175 in the CVD subcohort [417 myocardial infarction and stroke cases]). Relative abundances of 24 IgG N-glycan peaks (IgG-GPs) were measured by ultraperformance liquid chromatography, and eight glycosylation traits were derived based on structural similarity. End point-associated IgG-GPs were preselected with fractional polynomials, and prospective associations were estimated in confounder-adjusted Cox models. Diabetes risk associations were validated in three independent studies.

RESULTS

After adjustment for confounders and multiple testing correction, IgG-GP7, IgG-GP8, IgG-GP9, IgG-GP11, and IgG-GP19 were associated with type 2 diabetes risk. A score based on these IgG-GPs was associated with a higher diabetes risk in EPIC-Potsdam and independent validation studies (843 total cases, 3,149 total non-cases, pooled estimate per SD increase 1.50 [95% CI 1.37-1.64]). Associations of IgG-GPs with CVD risk differed between men and women. In women, IgG-GP9 was inversely associated with CVD risk (hazard ratio [HR] per SD 0.80 [95% CI 0.65-0.98]). In men, a weighted score based on IgG-GP19 and IgG-GP23 was associated with higher CVD risk (HR per SD 1.47 [95% CI 1.20-1.80]). In addition, several derived traits were associated with cardiometabolic disease incidence.

CONCLUSIONS

Selected IgG N-glycans are associated with cardiometabolic risk beyond classic risk factors, including clinical biomarkers.

In a pursuit of optimal glycan fluorescent label for negative MS mode for high-throughput N-glycan analysis

Over the past few decades, essential role of glycosylation in protein functioning has become widely recognized, rapidly advancing glycan analysis techniques. Because free glycan’s lack chromophore or fluorophore properties, and do not ionize well, they are often derivatized to facilitate their separation or detection, and to enhance the sensitivity of the analysis. Released glycan’s are usually derivatized using a fluorescent tag, which enables their optical detection in LC profiling. Some fluorescent labels can also promote ionization efficiency, thus facilitating MS detection. For this reason, there is a need to design fluorophores that will contribute more to the fluorescence and ionization of glycan’s and the need to quantify these contributions to improve glycan analysis methods. In this paper we focused on negative MS mode as these methods are more informative than methods involving positive MS mode, allowing for a less ambiguous elucidation of detailed glycan structures. Additionally, traditional glycan labels in negative mode MS usually result with diminished sensitivity compared to positive mode, thus making selection of appropriate label even more important for successful high-throughput analysis. Therefore, eleven fluorescent labels of different chemo-physical properties were chosen to study the influence of label hydrophobicity and presence of a negative charge on glycan ionization in negative MS mode. N-glycans released from IgG sample were labeled with one of the eleven labels, purified with HILIC-SPE and analyzed with HILIC-UPLC-FLR-MS. To make evaluation of studied labels performance more objective, analysis was performed in two laboratories and at two mobile phase pH (4.4 and 7.4). Although there was a notable trend of more hydrophobic labels having bigger signal intensities in one laboratory, we observed no such trend in the other laboratory. The results show that MS parameters and intrinsic configuration of the spectrometer have even bigger effect on the final ESI response of the labeled-glycan ionization in negative MS mode that the labels themselves. With this in mind, further research and development of fluorophores that will be suitable for high-throughput glycan analysis in the negative MS mode are proposed.

Glycan microarrays from construction to applications

Through their specific interactions with proteins, cellular glycans play key roles in a wide range of physiological and pathological processes. One of the main goals of research in the areas of glycobiology and glycomedicine is to understand glycan-protein interactions at the molecular level. Over the past two decades, glycan microarrays have become powerful tools for the rapid evaluation of interactions between glycans and proteins. In this review, we briefly describe methods used for the preparation of glycan probes and the construction of glycan microarrays. Next, we highlight applications of glycan microarrays to rapid profiling of glycan-binding patterns of plant, animal and pathogenic lectins, as well as other proteins. Finally, we discuss other important uses of glycan microarrays, including the rapid analysis of substrate specificities of carbohydrate-active enzymes, the quantitative determination of glycan-protein interactions, discovering high-affinity or selective ligands for lectins, and identifying functional glycans within cells. We anticipate that this review will encourage researchers to employ glycan microarrays in diverse glycan-related studies.

Metabolic Glycan Labeling of Cancer Cells Using Variably Acetylated Monosaccharides

Methylcyclopropene (Cyoc)-tagged tetra-acetylated monosaccharides, and in particular mannosamine derivatives, are promising tools for medical imaging of cancer using metabolic oligosaccharide engineering and the extremely fast inverse electron-demand Diels-Alder bioorthogonal reaction. However, the in vivo potential of these monosaccharide derivatives has yet to be fully explored due to their low aqueous solubility. To address this issue, we sought to vary the extent of acetylation of Cyoc-tagged monosaccharides and probe its effect on the extent of glycan labeling in various cancer cell lines. We demonstrate that, in the case of AcxManNCyoc, tri- and diacetylated derivatives generated significantly enhanced cell labeling compared to the tetra-acetylated monosaccharide. In contrast, for the more readily soluble azide-tagged sugars, a decrease in acetylation led to decreased glycan labeling. Ac3ManNCyoc gave better labeling than the azido-tagged Ac4ManNAz and has significant potential for in vitro and in vivo imaging of glycosylated cancer biomarkers.

Electrospray Ionization Mass Spectrometry of Apolipoprotein CIII to Evaluate O-glycan Site Occupancy and Sialylation in Congenital Disorders of Glycosylation

Congenital disorders of glycosylation (CDG) are inherited metabolic diseases that affect the synthesis of glycoconjugates. Defects in mucin-type O-glycosylation occur independently or in combination with N-glycosylation disorders, and the profiling of the O-glycans of apolipoprotein CIII (apoCIII) by mass spectrometry (MS) can be used to support a diagnosis. The biomarkers are site occupancy and sialylation levels, which are indicated by the content of non-glycosylated apoCIII0a isoform and by the ratio of monosialylated apoCIII1 to disialylated apoCIII2 isoforms, respectively. In this report, electrospray ionization (ESI) quadrupole MS of apoCIII was used to identify these biomarkers. Among the instrumental parameters, the declustering potential (DP) induced the fragmentation of the O-glycan moiety including the Thr-GalNAc linkage, resulting in an increase in apoCIII0a ions. This incurs the risk of creating a false positive for reduced site occupancy. The apoCIII1/apoCIII2 ratio was substantially unchanged despite some dissociation of sialic acids. Therefore, appropriate DP settings are especially important when transferrin, which requires a higher DP, for N-glycosylation disorders is analyzed simultaneously with apoCIII in a single ESI MS measurement. Finally, a reference range of diagnostic biomarkers and mass spectra of apoCIII obtained from patients with SLC35A1-, TRAPPC11-, and ATP6V0A2-CDG are presented.

Integrative identification of immune-related key genes in atrial fibrillation using weighted gene coexpression network analysis and machine learning

Background

The immune system significantly participates in the pathologic process of atrial fibrillation (AF). However, the molecular mechanisms underlying this participation are not completely explained. The current research aimed to identify critical genes and immune cells that participate in the pathologic process of AF.

Methods

CIBERSORT was utilized to reveal the immune cell infiltration pattern in AF patients. Meanwhile, weighted gene coexpression network analysis (WGCNA) was utilized to identify meaningful modules that were significantly correlated with AF. The characteristic genes correlated with AF were identified by the least absolute shrinkage and selection operator (LASSO) logistic regression and support vector machine recursive feature elimination (SVM-RFE) algorithm.

Results

In comparison to sinus rhythm (SR) individuals, we observed that fewer activated mast cells and regulatory T cells (Tregs), as well as more gamma delta T cells, resting mast cells, and M2 macrophages, were infiltrated in AF patients. Three significant modules (pink, red, and magenta) were identified to be significantly associated with AF. Gene enrichment analysis showed that all 717 genes were associated with immunity- or inflammation-related pathways and biological processes. Four hub genes (GALNT16, HTR2B, BEX2, and RAB8A) were revealed to be significantly correlated with AF by the SVM-RFE algorithm and LASSO logistic regression. qRT–PCR results suggested that compared to the SR subjects, AF patients exhibited significantly reduced BEX2 and GALNT16 expression, as well as dramatically elevated HTR2B expression. The AUC measurement showed that the diagnostic efficiency of BEX2, HTR2B, and GALNT16 in the training set was 0.836, 0.883, and 0.893, respectively, and 0.858, 0.861, and 0.915, respectively, in the validation set.

Conclusions

Three novel genes, BEX2, HTR2B, and GALNT16, were identified by WGCNA combined with machine learning, which provides potential new therapeutic targets for the early diagnosis and prevention of AF.

Specific N-glycans regulate an extracellular adhesion complex during somatosensory dendrite patterning

N-glycans are molecularly diverse sugars borne by over 70% of proteins transiting the secretory pathway and have been implicated in protein folding, stability, and localization. Mutations in genes important for N-glycosylation result in congenital disorders of glycosylation that are often associated with intellectual disability. Here, we show that structurally distinct N-glycans regulate an extracellular protein complex involved in the patterning of somatosensory dendrites in Caenorhabditis elegans. Specifically, aman-2/Golgi alpha-mannosidase II, a conserved key enzyme in the biosynthesis of specific N-glycans, regulates the activity of the Menorin adhesion complex without obviously affecting the protein stability and localization of its components. AMAN-2 functions cell-autonomously to allow for decoration of the neuronal transmembrane receptor DMA-1/LRR-TM with the correct set of high-mannose/hybrid/paucimannose N-glycans. Moreover, distinct types of N-glycans on specific N-glycosylation sites regulate DMA-1/LRR-TM receptor function, which, together with three other extracellular proteins, forms the Menorin adhesion complex. In summary, specific N-glycan structures regulate dendrite patterning by coordinating the activity of an extracellular adhesion complex, suggesting that the molecular diversity of N-glycans can contribute to developmental specificity in the nervous system.

GANAB and N-Glycans Substrates Are Relevant in Human Physiology, Polycystic Pathology and Multiple Sclerosis: A Review

Glycans are one of the four fundamental macromolecular components of living matter, and they are highly regulated in the cell. Their functions are metabolic, structural and modulatory. In particular, ER resident N-glycans participate with the Glc3Man9GlcNAc2 highly conserved sequence, in protein folding process, where the physiological balance between glycosylation/deglycosylation on the innermost glucose residue takes place, according GANAB/UGGT concentration ratio. However, under abnormal conditions, the cell adapts to the glucose availability by adopting an aerobic or anaerobic regimen of glycolysis, or to external stimuli through internal or external recognition patterns, so it responds to pathogenic noxa with unfolded protein response (UPR). UPR can affect Multiple Sclerosis (MS) and several neurological and metabolic diseases via the BiP stress sensor, resulting in ATF6, PERK and IRE1 activation. Furthermore, the abnormal GANAB expression has been observed in MS, systemic lupus erythematous, male germinal epithelium and predisposed highly replicating cells of the kidney tubules and bile ducts. The latter is the case of Polycystic Liver Disease (PCLD) and Polycystic Kidney Disease (PCKD), where genetically induced GANAB loss affects polycystin-1 (PC1) and polycystin-2 (PC2), resulting in altered protein quality control and cyst formation phenomenon. Our topics resume the role of glycans in cell physiology, highlighting the N-glycans one, as a substrate of GANAB, which is an emerging key molecule in MS and other human pathologies.

De novo DHDDS variants cause a neurodevelopmental and neurodegenerative disorder with myoclonus

Subcellular membrane systems are highly enriched in dolichol, whose role in organelle homeostasis and endosomal-lysosomal pathway remains largely unclear besides being involved in protein glycosylation. DHDDS encodes for the catalytic subunit (DHDDS) of the enzyme cis-prenyltransferase (cis-PTase), involved in dolichol biosynthesis and dolichol-dependent protein glycosylation in the endoplasmic reticulum. An autosomal recessive form of retinitis pigmentosa (retinitis pigmentosa 59) has been associated with a recurrent DHDDS variant. Moreover, two recurring de novo substitutions were detected in a few cases presenting with neurodevelopmental disorder, epilepsy and movement disorder. We evaluated a large cohort of patients (n = 25) with de novo pathogenic variants in DHDDS and provided the first systematic description of the clinical features and long-term outcome of this new neurodevelopmental and neurodegenerative disorder. The functional impact of the identified variants was explored by yeast complementation system and enzymatic assay. Patients presented during infancy or childhood with a variable association of neurodevelopmental disorder, generalized epilepsy, action myoclonus/cortical tremor and ataxia. Later in the disease course, they experienced a slow neurological decline with the emergence of hyperkinetic and/or hypokinetic movement disorder, cognitive deterioration and psychiatric disturbances. Storage of lipidic material and altered lysosomes were detected in myelinated fibres and fibroblasts, suggesting a dysfunction of the lysosomal enzymatic scavenger machinery. Serum glycoprotein hypoglycosylation was not detected and, in contrast to retinitis pigmentosa and other congenital disorders of glycosylation involving dolichol metabolism, the urinary dolichol D18/D19 ratio was normal. Mapping the disease-causing variants into the protein structure revealed that most of them clustered around the active site of the DHDDS subunit. Functional studies using yeast complementation assay and in vitro activity measurements confirmed that these changes affected the catalytic activity of the cis-PTase and showed growth defect in yeast complementation system as compared with the wild-type enzyme and retinitis pigmentosa-associated protein. In conclusion, we characterized a distinctive neurodegenerative disorder due to de novo DHDDS variants, which clinically belongs to the spectrum of genetic progressive encephalopathies with myoclonus. Clinical and biochemical data from this cohort depicted a condition at the intersection of congenital disorders of glycosylation and inherited storage diseases with several features akin to of progressive myoclonus epilepsy such as neuronal ceroid lipofuscinosis and other lysosomal disorders.

Insight on molecular pathogenesis and pharmacochaperoning potential in phosphomannomutase 2 deficiency, provided by novel human phosphomannomutase 2 structures

Phosphomannomutase 2 (PMM2) deficiency, the most frequent congenital disorder of glycosylation (PMM2-CDG), is a severe condition, which has no cure. Due to the identification of destabilizing mutations, our group aims at increasing residual activity in PMM2-CDG patients, searching for pharmacochaperones. Detailed structural knowledge of hPMM2 might help identify variants amenable to pharmacochaperoning. hPMM2 structural information is limited to one incomplete structure deposited in the Protein Databank without associated publication, which lacked ligands and residues from a crucial loop. Here we report five complete crystal structures of hPMM2, three for wild-type and two for the p.Thr237Met variant frequently found among Spanish PMM2-CDG patients, free and bound to the essential activator glucose-1,6-bisphosphate (Glc-1,6-P₂ ). In the hPMM2 homodimer, each subunit has a different conformation, reflecting movement of the distal core domain relative to the dimerization cap domain, supporting an opening/closing process during catalysis. Two Mg²⁺ ions bind to the core domain, one catalytic and one structural. In the cap domain, the site for Glc-1,6-P₂ is well delineated, while a Cl^- ion binding at the intersubunit interface is predicted to strengthen dimerization. Patient-found amino acid substitutions are nonhomogeneously distributed throughout hPMM2, reflecting differential functional or structural importance for various parts of the protein. We classify 93 of 101 patient-reported single amino acid variants according to five potential pathogenetic mechanism affecting folding of the core and cap domains, linker 2 flexibility, dimerization, activator binding, and catalysis. We propose that ~80% and ~50% of the respective core and cap domains substitutions are potential candidates for pharmacochaperoning treatment.

Severe phenotypes of B3GAT3-related disorder caused by two heterozygous variants: a case report and literature review

Background

Linkeropathies refers to a series of extremely rare hereditary connective tissue diseases affected by various glycosyltransferases in the biosynthesis of proteoglycans. We report for the first time two heterozygous variants of B3GAT3 in a Chinese infant, in whom Marfan syndrome was suspected at birth.

Case presentation

A 2-month-old boy from a non-consanguineous Chinese family without a family history presented severe phenotypes of joint dislocation, obvious flexion contractures of the elbow, arachnodactyly with slightly adducted thumbs, cranial dysplasia, foot abnormalities and aortic root dilation; Marfan syndrome was suspected at birth. Our patient was the youngest, at the age of 2 months, to experience aortic root dilation. Two B3GAT3 variants, NM_012200.2, c.752T>C, p.V251A and c.47C>A, p.S16*, with heterozygosity were identified in the patient by whole-exome sequencing; the variants were inherited from his parents. During close follow-up, significant changes in the cranial profile and obvious external hydrocephalus were present at the age of 7 months, which differs from previously reported cases.

Conclusion

We diagnosed a patient with congenital heart defects at an early age with a B3GAT3-related disorder instead of Marfan syndrome and expanded the spectrum of B3GAT3-related disorders. We also provide a literature review of reported B3GAT3 cases; for at least one of the variants, this is the first report of genotype–phenotype correlations in individuals with cardiovascular defects being related to the acceptor substrate-binding subdomain of B3GAT3.

Supply chain logistics - the role of the Golgi complex in extracellular matrix production and maintenance

The biomechanical and biochemical properties of connective tissues are determined by the composition and quality of their extracellular matrix. This, in turn, is highly dependent on the function and organisation of the secretory pathway. The Golgi complex plays a vital role in directing matrix output by co-ordinating the post-translational modification and proteolytic processing of matrix components prior to their secretion. These modifications have broad impacts on the secretion and subsequent assembly of matrix components, as well as their function in the extracellular environment. In this Review, we highlight the role of the Golgi in the formation of an adaptable, healthy matrix, with a focus on proteoglycan and procollagen secretion as example cargoes. We then discuss the impact of Golgi dysfunction on connective tissue in the context of human disease and ageing.

N- and O-glycan analysis for the detection of glycosylation disorders

Background

Congenital disorders of glycosylation (CDGs) are defined as a group of several rare autosomal recessive inborn errors of metabolism that affect the glycosylation of many proteins and/or lipids. Variable clinical presentation is very characteristic for all types of CDGs; symptoms include severe neurological manifestations that usually start in the neonatal period and cause aggressive irreversible neurological damage. These disorders are usually misdiagnosed as other non-inheritable disorders or remain undiagnosed for a long time, leading to severe neurological complications. The diagnosis of CDGs is quite tedious due to their diverse clinical presentation. In Egypt, there is still no available screening programme to detect CDGs in patients at a young age. Therefore, the need for a reliable rapid test that uses a small sample size has emerged.

This study included 50 suspected subjects and 50 healthy controls with matching age and sex. Western blotting and liquid chromatography-tandem mass spectrometry were used for the analysis of N- and O-glycans, respectively.

Results

The study detected 9 patients with hypoglycosylation (18%). Eight of the nine patients showed abnormal separation of N-glycoproteins using Western blotting indicative of reduced glycosylation (16% of the study subjects and 89% of the subjects with hypoglycosylation). Only one of the nine patients showed a decreased level of sialyl-T-antigen with a normal T-antigen level leading to an increased T/ST ratio (2% of study subjects and 11% of the subjects with hypoglycosylation).

Conclusion

Although N- and O-glycan analysis did not determine the underlying type of CDG, it successfully detected hypoglycosylation in 9 clinically suspected patients (18% of the studied subjects). All detected CDG cases were confirmed by molecular analysis results of mutations causing 4 different types of congenital disorders of glycosylation.

Efficient Preparation and Bioactivity Evaluation of Glycan-Defined Glycoproteins

Owing to the generation of heterogeneous glycoproteins in cells, it is highly difficult to study glycoprotein-mediated biological events and to develop biomedical agents. Thus, general and efficient methods to prepare homogeneous glycoproteins are in high demand. Herein, we report a general method for the efficient preparation of homogeneous glycoproteins that utilizes a combination of genetic code expansion and chemoselective ligation techniques. In the protocol to produce glycan-defined glycoproteins, an alkyne tag-containing protein, generated by genetic encoding of an alkynylated unnatural amino acid, was quantitatively coupled via click chemistry to versatile azide-appended glycans. The glycoproteins produced by the present strategy were found to recognize mammalian cell-surface lectins and enter the cells through lectin-mediated internalization. Also, cell studies exhibited that the glycoprotein containing multiple mannose-6-phosphate residues enters diseased cells lacking specific lysosomal glycosidases by binding to the cell-surface M6P receptor, and subsequently migrates to lysosomes for efficient degradation of stored glycosphingolipids.

N-Glycomic Analysis of the Cell Shows Specific Effects of Glycosyl Transferase Inhibitors

Glycomic profiling methods were used to determine the effect of metabolic inhibitors on glycan production. These inhibitors are commonly used to alter the cell surface glycosylation. However, structural analysis of the released glycans has been limited. In this research, the cell membranes were enriched and the glycans were released to obtain the N-glycans of the glycocalyx. Glycomic analysis using liquid chromatography–mass spectrometry (LC–MS) with a PGC chip column was used to profile the structures in the cell membrane. Glycans of untreated cells were compared to glycans of cells treated with inhibitors, including kifunensine, which inhibits the formation of complex- and hybrid-type structures, 2,4,7,8,9-Penta-O-acetyl-N-acetyl-3-fluoro-b-d-neuraminic acid methyl ester for sialylated glycans, 2-deoxy-2-fluorofucose, and 6-alkynyl fucose for fucosylated glycans. Kifunensine was the most effective, converting nearly 95% of glycans to high mannose types. The compound 6-alkynyl fucose inhibited some fucosylation but also incorporated into the glycan structure. Proteomic analysis of the enriched membrane for the four inhibitors showed only small changes in the proteome accompanied by large changes in the N-glycome for Caco-2. Future works may use these inhibitors to study the cellular behavior associated with the alteration of glycosylation in various biological systems, e.g., viral and bacterial infection, drug binding, and cell–cell interactions.

Glycan-specific antibodies as potential cancer biomarkers: a focus on microarray applications

Glycosylation is one of the most common posttranslational modifications of proteins and lipids. In the case of tumors, cell transformation accompanied by aberrant glycosylation results in the expression of tumor-associated glycans that promote tumor invasion. As part of the innate immunity, anti-glycan antibodies recognize tumor-associated glycans, and these antibodies can be present in the bloodstream in the early stages of cancer. Recently, anti-glycan antibody profiles have been of interest in various cancer studies. Novel advantages in the field of analytical techniques have simplified the analysis of anti-glycan antibodies and made it easier to have more comprehensive knowledge about their functions. One of the robust approaches for studying anti-glycan antibodies engages in microarray technology. The analysis of glycan microarrays can provide more expanded information to simultaneously specify or suggest the role of antibodies to a wide variety of glycans in the progression of different diseases, therefore making it possible to identify new biomarkers for diagnosing cancer and/or the state of the disease. Thus, in this review, we discuss antibodies to various glycans, their application for diagnosing cancer and one of the most promising tools for the investigation of these molecules, microarrays.

Identification of novel potential interaction partners of UDP-galactose (SLC35A2), UDP-N-acetylglucosamine (SLC35A3) and an orphan (SLC35A4) nucleotide sugar transporters

Nucleotide sugar transporters (NSTs) are ER and Golgi-resident members of the solute carrier 35 (SLC35) family which supply substrates for glycosylation by exchanging lumenal nucleotide monophosphates for cytosolic nucleotide sugars. Defective NSTs have been associated with congenital disorders of glycosylation (CDG), however, molecular basis of many types of CDG remains poorly characterized. To better understand the biology of NSTs, we identified potential interaction partners of UDP-galactose transporter (SLC35A2), UDP-N-acetylglucosamine transporter (SLC35A3) and an orphan nucleotide sugar transporter SLC35A4 of to date unassigned specificity. For this purpose, each of the SLC35A2-A4 proteins was used as a bait in four independent pull-down experiments and the identity of the immunoprecipitated material was discovered using MS techniques. From the candidate list obtained, we selected a few for which the interaction was confirmed in vitro using the NanoBiT system, a split luciferase-based luminescent technique. NSTs have been shown to interact with two ATPases (ATP2A2, ATP2C1), Golgi pH regulator B (GPR89B) and calcium channel (TMCO1), which may reflect the regulation of glycosylation by ion homeostasis, and with basigin (BSG). Our findings provide a starting point for the NST interaction network discovery in order to better understand how glycosylation is regulated and linked to other cellular processes. SIGNIFICANCE: Despite the facts that nucleotide sugar transporters are a key component of the protein glycosylation machinery, and deficiencies in their activity underlie serious metabolic diseases, biology, function and regulation of these essential proteins remain enigmatic. In this study we have advanced the field by identifying sets of new potential interaction partners for UDP-galactose transporter (SLC35A2), UDP-N-acetylglucosamine transporter (SLC35A3) and an orphan transporter SLC35A4 of yet undefined role. Several of these new interactions were additionally confirmed in vitro using the NanoBiT system, a split luciferase complementation assay. This work is also significant in that it addresses the overall challenge of discovering membrane protein interaction partners by a detailed comparison of 4 different co-immunoprecipitation strategies and by custom sample preparation and data processing workflows.

The effect of n-3 polyunsaturated fatty acids enriched hen eggs consumption on IgG and total plasma protein N-glycosylation in healthy individuals and cardiovascular patients

OBJECTIVE

This study determined the effect of n-3 PUFAs enriched hen eggs consumption on IgG and total plasma protein N-glycan profiles and inflammatory biomarkers level in healthy individuals (N = 33) and cardiovascular (CV) patients (N = 21).

MATERIALS AND METHODS

Subjects were divided to Control-Healthy and Control-CV subgroups (consumed three regular hens' eggs/daily (249 mg n-3 PUFAs/day)), and n-3-PUFAs-Healthy and n-3-PUFAs-CV subgroups (consumed three n-3 PUFAs enriched hen eggs/daily (1053 mg n-3 PUFAs/day)) for 3 weeks. Serum free fatty acids profile and high-sensitivity C reactive protein (hsCRP), interleukin 6 and 10 (IL-6, IL-10) and tumor necrosis factor alpha were measured. Total plasma protein and IgG N-glycome have been profiled before and after dietary protocols.

RESULTS

Serum n-3 PUFAs concentration significantly increased following n-3 PUFAs hen eggs consumption in both n-3-PUFAs-Healthy and n-3-PUFAs-CV. IL-10 significantly increased in both Healthy subgroups, while no change occurred in CV subgroups. Derived IgG N-glycan traits: bisecting GlcNAc (B) significantly decreased in n-3-PUFAs-Healthy, while agalactosylation (G0) and core fucosylation (CF) significantly increased in Control-Healthy. Derived total plasma protein N-glycan traits: high branching glycans (HB), trigalactosylation (G3), tetragalactosylation (G4), trisialylation (S3), tetrasialylation (S4) and antennary fucosylation (AF) significantly decreased, while G0, monogalactosylation (G1), neutral glycans (S0), B, CF and oligomannose structures (OM) significantly increased in n-3 PUFAs-CV. Digalactosylation (G2) significantly decreased, and G0, G1, S0, disialylation (S2), B and CF significantly increased in Control-CV.

CONCLUSIONS

n-3 PUFAs consumption alters IgG N-glycan traits and IL-10 in healthy individuals, and total plasma protein N-glycan traits in CV patients, by shifting them toward less inflammatory N-glycosylation profile.

Non-Covalent Microarrays from Synthetic Amino-Terminating Glycans-Implications in Expanding Glycan Microarray Diversity and Platform Comparison

Glycan microarrays have played important roles in detection and specificity assignment of glycan-recognition by proteins. However, the size and diversity of glycan libraries in current microarray systems are small compared to estimated glycomes, and these may lead to missed detection or incomplete assignment. For microarray construction, covalent and non-covalent immobilization are the two types of methods used, but a direct comparison of results from the two platforms is required. Here we develop a chemical strategy to prepare lipid-linked probes from both naturally-derived aldehyde-terminating and synthetic amino-terminating glycans that addresses the two aspects: expansion of sequence-defined glycan libraries and comparison of the two platforms. We demonstrate the specific recognition by plant and mammalian lectins, carbohydrate-binding modules and antibodies, and the overall similarities from the two platforms. Our results provide new knowledge on unique glycan-binding specificities for the immune-receptor Dectin-1 towards β-glucans and the interaction of rotavirus P[19] adhesive protein with mucin O-glycan cores.

The Extracellular Domains of GluN Subunits Play an Essential Role in Processing NMDA Receptors in the ER

N-methyl-D-aspartate receptors (NMDARs) belong to a family of ionotropic glutamate receptors that play essential roles in excitatory neurotransmission and synaptic plasticity in the mammalian central nervous system (CNS). Functional NMDARs consist of heterotetramers comprised of GluN1, GluN2A-D, and/or GluN3A-B subunits, each of which contains four membrane domains (M1 through M4), an intracellular C-terminal domain, a large extracellular N-terminal domain composed of the amino-terminal domain and the S1 segment of the ligand-binding domain (LBD), and an extracellular loop between M3 and M4, which contains the S2 segment of the LBD. Both the number and type of NMDARs expressed at the cell surface are regulated at several levels, including their translation and posttranslational maturation in the endoplasmic reticulum (ER), intracellular trafficking via the Golgi apparatus, lateral diffusion in the plasma membrane, and internalization and degradation. This review focuses on the roles played by the extracellular regions of GluN subunits in ER processing. Specifically, we discuss the presence of ER retention signals, the integrity of the LBD, and critical N-glycosylated sites and disulfide bridges within the NMDAR subunits, each of these steps must pass quality control in the ER in order to ensure that only correctly assembled NMDARs are released from the ER for subsequent processing and trafficking to the surface. Finally, we discuss the effect of pathogenic missense mutations within the extracellular domains of GluN subunits with respect to ER processing of NMDARs.

Role of ceramides in the pathogenesis of diabetes mellitus and its complications

Diabetes mellitus (DM) is a systemic metabolic disease that affects 463 million adults worldwide and is a leading cause of cardiovascular disease, blindness, nephropathy, peripheral neuropathy, and lower-limb amputation. Lipids have long been recognized as contributors to the pathogenesis and pathophysiology of DM and its complications, but recent discoveries have highlighted ceramides, a class of bioactive sphingolipids with cell signaling and second messenger capabilities, as particularly important contributors to insulin resistance and the underlying mechanisms of DM complications. Besides their association with insulin resistance and pathophysiology of type 2 diabetes, evidence is emerging that certain species of ceramides are mediators of cellular mechanisms involved in the initiation and progression of microvascular and macrovascular complications of DM. Advances in our understanding of these associations provide unique opportunities for exploring ceramide species as potential novel therapeutic targets and biomarkers. This review discusses the links between ceramides and the pathogenesis of DM and diabetic complications and identifies opportunities for novel discoveries and applications.

Photo-induced radical thiol-ene chemistry: a versatile toolbox for peptide-based drug design

While the global market for peptide/protein-based therapeutics is witnessing significant growth, the development of peptide drugs remains challenging due to their low oral bioavailability, poor membrane permeability, and reduced metabolic stability. However, a toolbox of chemical approaches has been explored for peptide modification to overcome these obstacles. In recent years, there has been a revival of interest in photoinduced radical thiol-ene chemistry as a powerful tool for the construction of therapeutic peptides.

The Close Relationship between the Golgi Trafficking Machinery and Protein Glycosylation

Glycosylation is the most common post-translational modification of proteins; it mediates their correct folding and stability, as well as their transport through the secretory transport. Changes in N- and O-linked glycans have been associated with multiple pathological conditions including congenital disorders of glycosylation, inflammatory diseases and cancer. Glycoprotein glycosylation at the Golgi involves the coordinated action of hundreds of glycosyltransferases and glycosidases, which are maintained at the correct location through retrograde vesicle trafficking between Golgi cisternae. In this review, we describe the molecular machinery involved in vesicle trafficking and tethering at the Golgi apparatus and the effects of mutations in the context of glycan biosynthesis and human diseases.

Altered glycosylation in cancer: A promising target for biomarkers and therapeutics

Glycosylation is a well-regulated cell and microenvironment specific post-translational modification. Several glycosyltransferases and glycosidases orchestrate the addition of defined glycan structures on the proteins and lipids. Recent advances and systemic approaches in glycomics have significantly contributed to a better understanding of instrumental roles of glycans in health and diseases. Emerging research evidence recognized aberrantly glycosylated proteins as the modulators of the malignant phenotype of cancer cells. The Cancer Genome Atlas has identified alterations in the expressions of glycosylation-specific genes that are correlated with cancer progression. However, the mechanistic basis remains poorly explored. Recent researches have shown that specific changes in the glycan structures are associated with 'stemness' and epithelial-to-mesenchymal transition of cancer cells. Moreover, epigenetic changes in the glycosylation pattern make the tumor cells capable of escaping immunosurveillance mechanisms. The deciphering roles of glycans in cancer emphasize that glycans can serve as a source for the development of novel clinical biomarkers. The ability of glycans in intervening various stages of tumor progression and the biosynthetic pathways involved in glycan structures constitute a promising target for cancer therapy. Advances in the knowledge of innovative strategies for identifying the mechanisms of glycan-binding proteins are hoped to hold great potential in cancer therapy. This review discusses the fundamental role of glycans in regulating tumorigenesis and tumor progression and provides insights into the influence of glycans in the current tactics of targeted therapies in the clinical setting.

Glycan array analysis of Pholiota squarrosa lectin and other fucose-oriented lectins

The α(1,6)fucose residue attached to the N-glycoprotein core is suspected to play an essential role in the progression of several types of cancer. Lectins remain the first choice for probing glycan modifications, although they may lack specificity. Thus, efforts have been made to identify new lectins with a narrower core fucose (CF) detection profile. Here, we present a comparison of the classical Aleuria aurantia lectin (AAL), Lens culinaris agglutinin (LCA) and Aspergillus oryzae lectin (AOL) with the newer Pholiota squarrosa lectin (PhoSL), which has been described as being specific for core fucosylated N-glycans. To this end, we studied the binding profiles of the four lectins using mammalian glycan arrays from the Consortium of Functional Glycomics. To validate their glycan specificity, we probed AOL, LCA and PhoSL in western-blot assays using protein extracts from eight common colorectal cancer (CRC) lines and colorectal biopsies from a small cohort of patients with CRC. The results showed that (i) LCA and PhoSL were the most specific lectins for detecting the presence of CF in a concentration-dependent manner; (ii) PhoSL exhibited the highest N-glycan sequence restriction, with preferential binding to core fucosylated paucimannosidic-type N-glycans, (iii) the recognition ability of PhoSL was highly influenced by the presence of terminal N-acetyl-lactosamine; (iv) LCA bound to paucimannosidic, bi-antennary and tri-antennary core fucosylated N-glycans and (v) AOL and AAL exhibited broader specificity towards fucosylation. Together, our results support the choice of LCA as the most appropriate lectin for CF detection, as validated in protein extracts from CRC cell lines and tissue specimens from patients with CRC.

Essential Functions of Glycans in Human Epithelia Dissected by a CRISPR-Cas9-Engineered Human Organotypic Skin Model

The glycome undergoes characteristic changes during histogenesis and organogenesis, but our understanding of the importance of select glycan structures for tissue formation and homeostasis is incomplete. Here, we present a human organotypic platform that allows genetic dissection of cellular glycosylation capacities and systematic interrogation of the roles of distinct glycan types in tissue formation. We used CRISPR-Cas9 gene targeting to generate a library of 3D organotypic skin tissues that selectively differ in their capacity to produce glycan structures on the main types of N- and O-linked glycoproteins and glycolipids. This tissue library revealed distinct changes in skin formation associated with a loss of features for all tested glycoconjugates. The organotypic skin model provides phenotypic cues for the distinct functions of glycoconjugates and serves as a unique resource for further genetic dissection and identification of the specific structural features involved. The strategy is also applicable to other organotypic tissue models.

HILIC-UPLC-MS for high throughput and isomeric N-glycan separation and characterization in Congenital Disorders Glycosylation and human diseases

N-glycan analyses may serve uncovering disease-associated biomarkers, as well as for profiling distinctive changes supporting diagnosis of genetic disorders of glycan biosynthesis named congenital disorders of glycosylation (CDG). Strategies based on liquid chromatography (LC) preferentially coupled to electrospray ionization (ESI) - mass spectrometry (MS) have emerged as powerful analytical methods for N-glycan identification and characterization. To enhance detection sensitivity, glycans are commonly labelled with a functional tag prior to LC-MS analysis. Since most derivatization techniques are notoriously time-consuming, some commercial analytical kits have been developed to speed up N-deglycosylation and N-glycan labelling of glycoproteins of pharmaceutical and biological interest such as monoclonal antibodies (mAbs). We exploited the analytical capabilities of RapiFluor-MS (RFMS) to perform, by a slightly modified protocol, a detailed N-glycan characterization of total serum and single serum glycoproteins from specific patients with CDG (MAN1B1-CDG, ALG12-CDG, MOGS-CDG, TMEM199-CDG). This strategy, accomplished by Hydrophilic Interaction Chromatography (HILIC)-UPLC-ESI-MS separation of the RFMS derivatized N-glycans, allowed us to uncover structural details of patients serum released N-glycans, thus extending the current knowledge on glycan profiles in these individual glycosylation diseases. The applied methodology enabled to differentiate in some cases either structural isomers and isomers differing in the linkage type. All the here reported applications demonstrated that RFMS method, coupled to HILIC-UPLC-ESI-MS, represents a sensitive high throughput approach for serum N-glycome analysis and a valuable option for glycan detection and separation particularly for isomeric species.

Profiling of IgG N-glycome during mouse aging: Fucosylated diantennary glycans containing one Neu5Gc-linked LacNAc are associated with age

N-glycosylation of immunoglobulin G (IgG) has been reported to change in human aging and in some age-related diseases. To further understand the molecular processes that determine these alterations, a detailed examination of individual IgG N-glycans with aging remains required. Mouse is the most commonly used model animal in studies of aging and age-related diseases, and mice have the advantage of relatively controllable genetic and environment variations compared to human. In this study, we systemically investigated the changes in serum IgG N-glycome in C57BL/6 mice during aging at 12 time points (6-80 weeks) via ultraperformance liquid chromatography with fluorescence detection. The study demonstrated several important findings. First, four chromatographic IgG N-glycan peaks were identified for the first time, including a high-mannose glycan, a monoantennary glycan, and two afucosylated glycans. Second, most of the IgG glycan levels changed significantly and presented pronounced gender-related differences from 6 to 12 weeks. Interestingly, all the IgG glycan levels tended to be similar between male and female mice at 12 weeks. Third, the level of fucosylated diantennary glycans containing one N-glycolylneuraminic acid (Neu5Gc)-linked N-acetyllactosamine (LacNAc) decreased gradually and showed a significant negative correlation with age from 24 to 80 weeks (r = -0.716, p < 0.0001), which was not sex-specific. SIGNIFICANCE: More comprehensive profile of murine IgG N-glycans by ultraperformance liquid chromatography with fluorescence detection was shown in this study with four newly identified chromatographic murine IgG N-glycan peaks. The majority of IgG N-glycans showed substantial stage-specific changes and sex-related differences during mouse aging, indicating a strict regulatory mechanism of glycan synthesis. The level of fucosylated diantennary glycans containing one Neu5Gc-linked LacNAc was significantly negatively correlated with age from 24 to 80 weeks, suggesting its great potential as an aging biomarker. The detailed characteristics of IgG N-glycosylation with aging in C57BL/6 mice demonstrated in the present study could provide essential reference data for studying the function and mechanism of IgG glycosylation in age-related researches based on C57BL/6 mouse models.

Molecular signatures of tumor progression in myxoid liposarcoma identified by N-glycan mass spectrometry imaging

Myxoid liposarcoma (MLS) is the second most common subtype of liposarcoma, accounting for ~6% of all sarcomas. MLS is characterized by a pathognomonic FUS-DDIT3, or rarely EWSR1-DDIT3, gene fusion. The presence of ≥5% hypercellular round cell areas is associated with a worse prognosis for the patient and is considered high grade. The prognostic significance of areas with moderately increased cellularity (intermediate) is currently unknown. Here we have applied matrix-assisted laser desorption/ionization mass spectrometry imaging to analyze the spatial distribution of N-linked glycans on an MLS microarray in order to identify molecular markers for tumor progression. Comparison of the N-glycan profiles revealed that increased relative abundances of high-mannose type glycans were associated with tumor progression. Concomitantly, an increase of the average number of mannoses on high-mannose glycans was observed. Although overall levels of complex-type glycans decreased, an increase of tri- and tetra-antennary N-glycans was observed with morphological tumor progression and increased tumor histological grade. The high abundance of tri-antennary N-glycan species was also associated with poor disease-specific survival. These findings mirror recent observations in colorectal cancer, breast cancer, ovarian cancer, and cholangiocarcinoma, and are in line with a general role of high-mannose glycans and higher-antennary complex-type glycans in cancer progression.

Differential expression patterns of glycosphingolipids and C-type lectin receptors on immune cells in absence of functional regulatory T cells

Background

Glycosylation is a common and complex type of protein posttranslational modification. Altered glycosylation of immunoglobulins in autoimmune diseases has led to the “altered glycan hypothesis” postulating existence of a unique glycan signature on immune cells and extracellular proteins characterized by site‐specific relative abundances of individual glycan structures and glycosylation patterns. However, it is not clear how glycosylation on leukocyte subpopulations differ between states of health or inflammation.

Hypothesis

Glycosphingolipid patterns on immune cells of forkhead‐box‐P3‐deficient scurfy mice differs from those on wild‐type immune cells.

Methods

T cells and dendritic cells were isolated from spleens of either wild‐type or age‐matched scurfy mice. Glycosphingolipids of CD4⁺ T cells and splenic dendritic cells from wild‐type and scurfy mice were then analyzed by multiplexed capillary gel electrophoresis coupled to laser‐induced fluorescence detection (xCGE‐LIF). In addition, flow cytometry and ChipCytometry were used to access expression patterns of various C‐type lectin receptors on antigen‐presenting cells from various organs of both wild‐type and scurfy mice.

Results

We, hereby report differential expression of glycosphingolipids in health and under inflammatory conditions as reflected in wild‐type and scurfy mice. Furthermore, we observed that the absence of functional regulatory T cells correlated with elevated expression of CLEC‐7A and CD205 but a reduction in levels of CLEC12A and CD206 on antigen‐presenting cells.

Conclusion

We hereby show that the absence of functional regulatory T cells affects expression pattern and quantities of glycosphingolipids on immune cells. Thus, glycosphingolipids could serve as biomarkers for mapping genetical and homeostatic perturbances such as those resulting from a diseased condition.

Sugary Logistics Gone Wrong: Membrane Trafficking and Congenital Disorders of Glycosylation

Glycosylation is an important post-translational modification for both intracellular and secreted proteins. For glycosylation to occur, cargo must be transported after synthesis through the different compartments of the Golgi apparatus where distinct monosaccharides are sequentially bound and trimmed, resulting in increasingly complex branched glycan structures. Of utmost importance for this process is the intraorganellar environment of the Golgi. Each Golgi compartment has a distinct pH, which is maintained by the vacuolar H+-ATPase (V-ATPase). Moreover, tethering factors such as Golgins and the conserved oligomeric Golgi (COG) complex, in concert with coatomer (COPI) and soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE)-mediated membrane fusion, efficiently deliver glycosylation enzymes to the right Golgi compartment. Together, these factors maintain intra-Golgi trafficking of proteins involved in glycosylation and thereby enable proper glycosylation. However, pathogenic mutations in these factors can cause defective glycosylation and lead to diseases with a wide variety of symptoms such as liver dysfunction and skin and bone disorders. Collectively, this group of disorders is known as congenital disorders of glycosylation (CDG). Recent technological advances have enabled the robust identification of novel CDGs related to membrane trafficking components. In this review, we highlight differences and similarities between membrane trafficking-related CDGs.

Recent Progress in Chemo-Enzymatic Methods for the Synthesis of N-Glycans

Asparagine (N)-linked glycosylation is one of the most common co- and post-translational modifications of both intra- and extracellularly distributing proteins, which directly affects their biological functions, such as protein folding, stability and intercellular traffic. Production of the structural well-defined homogeneous N-glycans contributes to comprehensive investigation of their biological roles and molecular basis. Among the various methods, chemo-enzymatic approach serves as an alternative to chemical synthesis, providing high stereoselectivity and economic efficiency. This review summarizes some recent advances in the chemo-enzymatic methods for the production of N-glycans, including the preparation of substrates and sugar donors, and the progress in the glycosyltransferases characterization which leads to the diversity of N-glycan synthesis. We discuss the bottle-neck and new opportunities in exploiting the chemo-enzymatic synthesis of N-glycans based on our research experiences. In addition, downstream applications of the constructed N-glycans, such as automation devices and homogeneous glycoproteins synthesis are also described.

Targeting Glycoproteins as a therapeutic strategy for diabetes mellitus and its complications

OBJECTIVES

Glycoproteins are organic compounds formed from proteins and carbohydrates, which are found in many parts of the living systems including the cell membranes. Furthermore, impaired metabolism of glycoprotein components plays the main role in the pathogenesis of diabetes mellitus. The aim of this study is to investigate the influence of glycoprotein levels in the treatment of diabetes mellitus.

METHODS

All relevant papers in the English language were compiled by searching electronic databases, including Scopus, PubMed and Cochrane library. The keywords of glycoprotein, diabetes mellitus, glycan, glycosylation, and inhibitor were searched until January 2019.

RESULTS

Glycoproteins are pivotal elements in the regulation of cell proliferation, growth, maturation and signaling pathways. Moreover, they are involved in drug binding, drug transportation, efflux of chemicals and stability of therapeutic proteins. These functions, structure, composition, linkages, biosynthesis, significance and biological effects are discussed as related to their use as a therapeutic strategy for the treatment of diabetes mellitus and its complications.

CONCLUSIONS

The findings revealed several chemical and natural compounds have significant beneficial effects on glycoprotein metabolism. The comprehension of glycoprotein structure and functions are very essential and inevitable to enhance the knowledge of glycoengineering for glycoprotein-based therapeutics as may be required for the treatment of diabetes mellitus and its associated complications. Graphical abstract.

Chemical synthesis of 5'-β-glycoconjugates of vitamin B6

Various 5'-β-saccharides of pyridoxine, namely the mannoside, galactoside, arabinoside, maltoside, cellobioside and glucuronide, were synthesized chemically according to Koenigs-Knorr conditions using α4,3-O-isopropylidene pyridoxine and the respective acetobromo glycosyl donors with AgOTf (3.0 eq.) and NIS (3.0 eq.) as promoters at 0 °C. Furthermore, 5'-β-[¹³C₆]-labeled pyridoxine glucoside (PNG) was prepared starting from [¹³C₆]-glucose and pyridoxine. Additionally, two strategies were examined for the synthesis of 5'-β-pyridoxal glucoside (PLG).

Nonimmune hydrops fetalis and congenital disorders of glycosylation: A systematic literature review

Numerous etiologies may lead to nonimmune hydrops fetalis (NIHF) including congenital disorders of glycosylation (CDG). Recognition of CDG in NIHF is challenging. This study reviews prenatal and neonatal characteristics of CDG presenting with NIHF. A systematic literature search was performed. Thirteen articles met the inclusion criteria. Twenty-one cases with NIHF associated with a CDG were reported. There were 17 live births, three pregnancy terminations, and one fetal demise. Timing of CDG diagnosis was reported mostly postnatally (90%; 10/11). Postnatal genetic testing was reported in 18 patients; three patients were diagnosed by isoelectric focusing of serum transferrin that showed a type 1 pattern. The genes reported for CDG with NIHF for 15 distinct families include: PMM2 in 47% (7/15), ALG9 in 20% (3/15), ALG8 in 13% (2/15), ALG1 in 7% (1/15), MGAT2 in 7% (1/15), and COG6 7% (1/15). In our review, 81% (17/21) reported facial dysmorphism, 52% (11/21) reported CNS abnormalities, most commonly cerebellar atrophy (64%; 7/11), and 38% (8/21) reported cardiovascular abnormalities, most commonly hypertrophic cardiomyopathy (63%; 5/8). Among live births, 71% (12/17) infants died at a median age of 34 days (range 1-185). Thrombocytopenia was reported in 53% (9/17) patients. Of those who survived past the neonatal period, 80% (4/5) had significant reported developmental delays. CDG should be on the differential diagnosis of NIHF in the presence of cerebellar atrophy, hypertrophic cardiomyopathy, or thrombocytopenia. Our review highlights the poor prognosis in infants with NIHF due to CDG and demonstrates the importance of identifying these disorders prenatally to guide providers in their counseling with families regarding pregnancy management. SYNOPSIS: Poor prognosis in fetuses and infants with nonimmune hydrops fetalis due to congenital disorders of glycosylation highlights the importance of prenatal diagnosis of this disorder.

Glycosylation of immunoglobulin G is regulated by a large network of genes pleiotropic with inflammatory diseases

Effector functions of immunoglobulin G (IgG) are regulated by the composition of a glycan moiety, thus affecting activity of the immune system. Aberrant glycosylation of IgG has been observed in many diseases, but little is understood about the underlying mechanisms. We performed a genome-wide association study of IgG N-glycosylation (N = 8090) and, using a data-driven network approach, suggested how associated loci form a functional network. We confirmed in vitro that knockdown of IKZF1 decreases the expression of fucosyltransferase FUT8, resulting in increased levels of fucosylated glycans, and suggest that RUNX1 and RUNX3, together with SMARCB1, regulate expression of glycosyltransferase MGAT3. We also show that variants affecting the expression of genes involved in the regulation of glycoenzymes colocalize with variants affecting risk for inflammatory diseases. This study provides new evidence that variation in key transcription factors coupled with regulatory variation in glycogenes modifies IgG glycosylation and has influence on inflammatory diseases.