The emerging significance of O-GlcNAc in cellular regulation

A novel 2D-electrophoresis method for the simultaneous visualization of phosphorylated and O-GlcNAcylated proteoforms of a protein

Post-translational modifications (PTMs), such as phosphorylation and O-N-acetyl-β-d-glucosaminylation (O-GlcNAcylation), are involved in the fine spatiotemporal regulation of protein functions, and their dynamic interplay is at the heart of protein language. The coexistence of phosphorylation and O-GlcNAcylation on a protein leads to the diversification of proteoforms. It is therefore essential to decipher the phosphorylation/O-GlcNAcylation interplay on protein species that orchestrates cellular processes in a specific physiological or pathophysiological context. However, simultaneous visualization of phosphorylation and O-GlcNAcylation patterns on a protein of interest remains a challenge. To map the proteoforms of a protein, we have developed an easy-to-use two-dimensional electrophoresis method with a single sample processing permitting simultaneous visualization of the phosphorylated and the O-GlcNAcylated forms of the protein of interest. This method, we termed 2D-WGA-Phos-tag-PAGE relies on proteoforms retardation by affinity gel electrophoresis. With this novel approach, we established the cartography of phospho- and glycoforms of αB-crystallin and desmin in the whole extract and the cytoskeleton protein subfraction in skeletal muscle cells. Interestingly, we have shown that the pattern of phosphorylation and O-GlcNAcylation depends of the subcellular subfraction. Moreover, we have also shown that proteotoxic stress condition increased the complexity of the pattern of PTMs on αB-crystallin.

Multi-faceted regulation of CREB family transcription factors

cAMP response element-binding protein (CREB) is a ubiquitously expressed nuclear transcription factor, which can be constitutively activated regardless of external stimuli or be inducibly activated by external factors such as stressors, hormones, neurotransmitters, and growth factors. However, CREB controls diverse biological processes including cell growth, differentiation, proliferation, survival, apoptosis in a cell-type-specific manner. The diverse functions of CREB appear to be due to CREB-mediated differential gene expression that depends on cAMP response elements and multi-faceted regulation of CREB activity. Indeed, the transcriptional activity of CREB is controlled at several levels including alternative splicing, post-translational modification, dimerization, specific transcriptional co-activators, non-coding small RNAs, and epigenetic regulation. In this review, we present versatile regulatory modes of CREB family transcription factors and discuss their functional consequences.

Impact of MG132 induced-proteotoxic stress on αB-crystallin and desmin phosphorylation and O-GlcNAcylation and their partition towards cytoskeleton

Small Heat Shock Proteins are considered as the first line of defense when proteostasis fails. Among them, αB-crystallin is expressed in striated muscles in which it interacts with desmin intermediate filaments to stabilize them, maintaining cytoskeleton's integrity and muscular functionalities. Desmin is a key actor for muscle health; its targeting by αB-crystallin is thus crucial, especially in stress conditions. αB-crystallin is phosphorylated and O-GlcNAcylated. Its phosphorylation increases consecutively to various stresses, correlated with its recruitment for cytoskeleton's safeguarding. However, phosphorylation as unique signal for cytoskeleton translocation remains controversial; indeed, O-GlcNAcylation was also proposed to be involved. Thus, there are still some gaps for a deeper comprehension of how αB-crystallin functions are finely regulated by post-translational modifications. Furthermore, desmin also bears both post-translational modifications; while desmin phosphorylation is closely linked to desmin intermediates filaments turnover, it is unclear whereas its O-GlcNAcylation could impact its proper function. In the herein paper, we aim at identifying whether phosphorylation and/or O-GlcNAcylation are involved in αB-crystallin targeting towards cytoskeleton in proteotoxic stress induced by proteasome inhibition in C2C12 myotubes. We demonstrated that proteotoxicity led to αB-crystallin's phosphorylation and O-GlcNAcylation patterns changes, both presenting a dynamic interplay depending on protein subfraction. Importantly, both post-translational modifications showed a spatio-temporal variation correlated with αB-crystallin translocation towards cytoskeleton. In contrast, we did not detect any change of desmin phosphorylation and O-GlcNAcylation. All together, these data strongly support that αB-crystallin phosphorylation/O-GlcNAcylation interplay rather than changes on desmin is a key regulator for its cytoskeleton translocation, preserving it towards stress.

Synthetic assembly of α-O-linked-type GlcNAc using polymer chemistry affords sugar clusters, which effectively bind to lectins

Fischer's glycoside synthesis was applied to linker precursor alcohols of two different lengths having appropriate alkane chains to obtain the corresponding α-glycoside and it was found to be applicable with moderate yields. Water-soluble glycomonomers were systematically prepared from N-acetyl-d-glucosamine (GlcNAc) by introducing two kinds of alcohols having different methylene lengths. Typical radical polymerizations of the glycomonomers with acrylamide as a modulator for control of the distance between carbohydrate residues in water in the presence of ammonium persulfate (APS)-N,N,N',N'-tetramethylethylenediamine (TEMED) gave a series of glycopolymers with various α-glycoside-type GlcNAc residue densities. Fluorometric analysis of the interaction of wheat germ agglutinin (WGA) with the glycopolymers was performed and the results showed unique binding specificities based on structural differences.

O-GlcNAc modification of GSDMD attenuates LPS-induced endothelial cells pyroptosis

OBJECTIVE

Increased O-linked β-N-acetylglucosamine (O-GlcNAc) stimulation has been reported to protect against sepsis associated mortality and cardiovascular derangement. Previous studies, including our own research, have indicated that gasdermin-D(GSDMD)-mediated endothelial cells pyroptosis contributes to sepsis-associated endothelial injury. This study explored the functions and mechanisms of O-GlcNAc modification on lipopolysaccharide (LPS)-induced pyroptosis and its effects on the function of GSDMD.

METHODS

A LPS-induced septic mouse model administrated with O-GlcNAcase (OGA) inhibitor thiamet-G (TMG) was used to assess the effects of O-GlcNAcylation on sepsis-associated vascular dysfunction and pyroptosis. We conducted experiments on human umbilical vein endothelial cells (HUVECs) by challenging them with LPS and TMG to investigate the impact of O-GlcNAcylation on endothelial cell pyroptosis and implications of GSDMD. Additionally, we identified potential O-GlcNAcylation sites in GSDMD by utilizing four public O-GlcNAcylation site prediction database, and these sites were ultimately established through gene mutation.

RESULTS

Septic mice with increased O-GlcNAc stimulation exhibited reduced endothelial injury, GSDMD cleavage (a marker of pyroptosis). O-GlcNAc modification of GSDMD mitigates LPS-induced pyroptosis in endothelial cells by preventing its interaction with caspase-11 (a human homologous of caspases-4/5). We also identified GSDMD Serine 338 (S338) as a novel site of O-GlcNAc modification, leading to decreased association with caspases-4 in HEK293T cells.

CONCLUSIONS

Our findings identified a novel post-translational modification of GSDMD and elucidated the O-GlcNAcylation of GSDMD inhibits LPS-induced endothelial injury, suggesting that O-GlcNAc modification-based treatments could serve as potential interventions for sepsis-associated vascular endothelial injury.

Targeting dysregulated lipid metabolism in the tumor microenvironment

The reprogramming of lipid metabolism and its association with oncogenic signaling pathways within the tumor microenvironment (TME) have emerged as significant hallmarks of cancer. Lipid metabolism is defined as a complex set of molecular processes including lipid uptake, synthesis, transport, and degradation. The dysregulation of lipid metabolism is affected by enzymes and signaling molecules directly or indirectly involved in the lipid metabolic process. Regulation of lipid metabolizing enzymes has been shown to modulate cancer development and to avoid resistance to anticancer drugs in tumors and the TME. Because of this, understanding the metabolic reprogramming associated with oncogenic progression is important to develop strategies for cancer treatment. Recent advances provide insight into fundamental mechanisms and the connections between altered lipid metabolism and tumorigenesis. In this review, we explore alterations to lipid metabolism and the pivotal factors driving lipid metabolic reprogramming, which exacerbate cancer progression. We also shed light on the latest insights and current therapeutic approaches based on small molecular inhibitors and phytochemicals targeting lipid metabolism for cancer treatment. Further investigations are worthwhile to fully understand the underlying mechanisms and the correlation between altered lipid metabolism and carcinogenesis.

Novel pseudonucleosides and sulfamoyl-oxazolidinone β-D-glucosamine derivative as anti-COVID-19: design, synthesis, and in silico study

New pseudonucleosides containing cyclic sulfamide moiety and sulfamoyl β-D-glucosamine derivative are described. These pseudonucleosides are synthesized in good yields starting from chlorosulfonyl isocyanate and β-D-glucosamine hydrochloride in five steps; (protection, acetylation, removal of the Boc group, sulfamoylation, and cyclization). Further, novel glycosylated sulfamoyloxazolidin-2-one is prepared in three steps; carbamoylation, sulfamoylation, and intramolecular cyclization. The structures of the synthesized compounds were confirmed by usual spectroscopic and spectrometric methods NMR, IR, MS, and EA. Interesting molecular docking of the prepared pseudonucleosides and (Beclabuvir, Remdesivir) drugs with SARS-CoV-2/Mpro (PDB:5R80) was conducted using the same parameters for a fair comparison. A low binding affinity of the synthesized compounds compared to the Beclabuvir and other analysis showed that pseudonucleosides have the ability to inhibit SARS-CoV-2. After the motivating results of molecular docking study, the complex between the SARS-CoV-2 Mpro and compound 7 was subjected to 100 ns molecular dynamics (MD) simulation using Desmond module of Schrodinger suite, during which the receptor-ligand complex showed substantial stability after 10 ns of MD simulation. Also, we studied the prediction of absorption, distribution, properties of metabolism, excretion, and toxicity (ADMET) of the synthesized compounds.Communicated by Ramaswamy H. Sarma.

One-Pot Synthesis of 2-C-Branched Glycosyl Triazoles by Integrating 1,2-Cyclopropanated Sugar Ring-Opening Azidation and CuAAC Reaction

A series of 2-C-branched glycosyl triazoles including triazole-tethered oligosaccharides and glycopeptides were synthesized in one pot from 1,2-cyclopropanated sugars or 2'-acetonyl-2-O-Ts-C-furanosides, NaN₃, and alkynes using PEG-400 as a single solvent. Nucleophilic ring-opening azidation of 1,2-cyclopropanated sugars (or 2'-acetonyl group 1,2-migration-azidation of C-furanosides) obtained glycosyl azides, which upon reaction with alkynes under CuAAC conditions achieved glycosyl triazoles in good yields and high stereoselectivity without the need to change the solvent and isolate any intermediates.

Extension of the CHARMM Classical Drude Polarizable Force Field to N- and O-Linked Glycopeptides and Glycoproteins

Molecular dynamic simulations are an effective tool to study complex molecular systems and are contingent upon the availability of an accurate and reliable molecular mechanics force field. The Drude polarizable force field, which allows for the explicit treatment of electronic polarization in a computationally efficient fashion, has been shown to reproduce experimental properties that were difficult or impossible to reproduce with the CHARMM additive force field, including peptide folding cooperativity, RNA hairpin structures, and DNA base flipping. Glycoproteins are essential components of glycoconjugate vaccines, antibodies, and many pharmaceutically important molecules, and an accurate polarizable force field that includes compatibility between the protein and carbohydrate aspect of the force field is essential to study these types of systems. In this work, we present an extension of the Drude polarizable force field to glycoproteins, including both N- and O-linked species. Parameter optimization focused on the dihedral terms using a reweighting protocol targeting NMR solution J-coupling data for model glycopeptides. Validation of the model include eight model glycopeptides and four glycoproteins with multiple N- and O-linked glycosylations. The new glycoprotein carbohydrate force field can be used in conjunction with the remainder of Drude polarizable force field through a variety of MD simulation programs including GROMACS, OPENMM, NAMD, and CHARMM and may be accessed through the Drude Prepper module in the CHARMM-GUI.

Potential Roles of PTEN on Longevity in Two Closely Related Argopecten Scallops With Distinct Lifespans

Phosphatase and tensin homolog deleted on chromosome ten (PTEN) has been found to regulate longevity through the PI3K/Akt/FoxO pathway and maintenance of genome integrity in worms, flies, and mammals. However, limited information is available on the roles of PTEN in longevity of aquatic animals. Here we extended this paradigm using two closely related Argopecten scallops, Argopecten purpuratus, and Argopecten irradians, with significantly distinct life spans, which are commercially important bivalve species for fishery and aquaculture in China, United States, Peru, and Chile. The ORFs of the ApPTEN and AiPTEN were 1,476 and 1,473 bp, which encoded 491 and 490 amino acids, respectively. There were 48 synonymous and 16 non-synonymous SNPs and one InDel of three nucleotides between ApPTEN and AiPTEN, resulting in variations in 15 amino acids and lack of S453 in AiPTEN. Differences in conformation and posttranslational modification were predicted between ApPTEN and AiPTEN, which may indicate different activities of ApPTEN and AiPTEN. When the animals were subjected to nutrition restriction, the expression of both ApPTEN and AiPTEN was upregulated, with AiPTEN responded faster and more robust than ApPTEN. Ionizing radiation induced significantly elevated expression of ApPTNE but not AiPTEN in the adductor muscle, and the mortality rate of A. purpuratus was significantly lower than that of A. irradians, indicating that ApPTNE may play a protective role by maintaining the genome integrity. RNAi of ApPTNE significantly downregulated the expression of its downstream regulated genes known to favor longevity, such as FoxO, Mn-SOD, and CAT. These results indicated that PTEN may contribute to the longevity of A. purpuratus through regulation of nutrient availability and genomic stability, probably via PI3K/Akt/FoxO pathway. Our study may provide new evidence for understanding of the conservative functions of PTEN in regulation of lifespan in animals and human, and it may also benefit the selection of scallops strains with long lifespan and thus larger size.

O‐GlcNAcylation regulates lysophosphatidic acid‐induced cell migration by regulating ERM family proteins

O‐GlcNAcylation of intracellular proteins (O‐GlcNAc) is a post‐translational modification that often competes with phosphorylation in diverse cellular signaling pathways. Recent studies on human malignant tumors have demonstrated that O‐GlcNAc is implicated in cellular features relevant to metastasis. Here, we report that lysophosphatidic acid (LPA)‐induced ovarian cancer cell (OVCAR‐3) migration is regulated by O‐GlcNAc. We found that O‐GlcNAc modification of ERM family proteins, a membrane‐cytoskeletal crosslinker, was inversely correlated with its phosphorylation status. Moreover, the LPA‐induced formation of membrane protrusion structures, as well as the migration of OVCAR‐3 cells, was reduced by the accumulation of O‐GlcNAc. Collectively, these findings suggest that O‐GlcNAc is an essential signaling element controlling ERM family proteins involved in OVCAR‐3 cell migration.

Demystifying the O-GlcNAc Code: A Systems View

Post-translational modification with O-linked β-N-acetylglucosamine (O-GlcNAc), a process referred to as O-GlcNAcylation, occurs on a vast variety of proteins. Mounting evidence in the past several decades has clearly demonstrated that O-GlcNAcylation is a unique and ubiquitous modification. Reminiscent of a code, protein O-GlcNAcylation functions as a crucial regulator of nearly all cellular processes studied. The primary aim of this review is to summarize the developments in our understanding of myriad protein substrates modified by O-GlcNAcylation from a systems perspective. Specifically, we provide a comprehensive survey of O-GlcNAcylation in multiple species studied, including eukaryotes (e.g., protists, fungi, plants, Caenorhabditis elegans, Drosophila melanogaster, murine, and human), prokaryotes, and some viruses. We evaluate features (e.g., structural properties and sequence motifs) of O-GlcNAc modification on proteins across species. Given that O-GlcNAcylation functions in a species-, tissue-/cell-, protein-, and site-specific manner, we discuss the functional roles of O-GlcNAcylation on human proteins. We focus particularly on several classes of relatively well-characterized human proteins (including transcription factors, protein kinases, protein phosphatases, and E3 ubiquitin-ligases), with representative O-GlcNAc site-specific functions presented. We hope the systems view of the great endeavor in the past 35 years will help demystify the O-GlcNAc code and lead to more fascinating studies in the years to come.

Boron Isotope Tag-Assisted Ultrahigh-Performance Liquid Chromatography Coupled with High-Resolution Mass Spectrometry for Discovery and Annotation of cis-Diol-Containing Metabolites

cis-Diol-containing metabolites are widely distributed in living organisms, and they participate in the regulation of various important biological activities. The profiling of cis-diol-containing metabolites could help us in fully understanding their functions. In this work, based on the characteristic isotope pattern of boron, we employed a boronic acid reagent as the isotope tag to establish a sensitive and selective liquid chromatography-high-resolution mass spectrometry method for the screening and annotation of cis-diol-containing metabolites in biological samples. Boronic acid reagent 2-methyl-4-phenylaminomethylphenylboronic acid was used to label the cis-diol-containing metabolites in biological samples to improve the selectivity and MS sensitivity of cis-diol-containing metabolites. Based on the characteristic 0.996 Da mass difference of precursor ions and the peak intensity ratio of 1:4 originating from ¹⁰B and ¹¹B natural isotopes, the potential cis-diol-containing metabolites were rapidly screened from biological samples. Potential cis-diol-containing metabolites were annotated by database searching and analysis of fragmentation patterns obtained by multistage MS (MSⁿ) via collision-induced dissociation. Importantly, the cis-diol position could be readily resolved by the MS³ spectrum. With this method, a total of 45 cis-diol-containing metabolites were discovered in rice, including monoglycerides, polyhydroxy fatty acids, fatty alcohols, and so forth. Furthermore, the established method showed superiority in avoiding false-positive results in profiling cis-diol-containing metabolites.

Prediction of human tau 3D structure, and interplay between O-β-GlcNAc and phosphorylation modifications in Alzheimer's disease: C. elegans as a suitable model to study these interactions in vivo

Tau protein regulates, maintains and stabilizes microtubule assembly under normal physiological conditions. In certain pathological circumstances, tau is post-translationally modified predominantly via phosphorylation and glycosylation. Hyper-phosphorylation of tau in Alzheimer's disease (AD) resulted in aggregated neurofibrillary tangles (NFTs) formation. Unfortunately, absence of tau 3D structure makes difficult to understand exact mechanism involved in tau pathology. Here by using ab-initio modelling, we predicted a tau 3D structure that not only explains its binding with microtubules but also elucidates NFTs formation. O-linked β-N-acetylglucosaminylation (O-β-GlcNAc) is thought to regulate tau phosphorylation on single or proximal Ser/Thr residues (called as Yin-Yang sites). In this study, we not only validate the previously described three-serine residues (208, 238 and 400) as Yin-Yang sites but also predicted 22 more possible Ser/Thr O-glycosylation sites. Among them seventeen residues were predicted as possible Yin-Yang sites and are proposed to mediate NFT formation in AD. These predicted Yin-Yang sites may act as attractive therapeutic targets for the drug development in AD. Predicted 3D structure of tau₄₄₁ was highly accessible for phosphorylation and hyperphosphorylation, and showed higher surface accessibility for interplay between O-β-GlcNAc and phosphorylation modifications. Kinases and phosphatases involved in tau phosphorylation are conserved in human and other organisms. Homology modelling revealed conserved catalytic domain for both human and C. elegans O-GlcNAc transferase (OGT), suggesting that transgenic C. elegans expressing human tau may be a suitable model system to study these modifications.

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.

McArdle Disease: New Insights into Its Underlying Molecular Mechanisms

McArdle disease, also known as glycogen storage disease type V (GSDV), is characterized by exercise intolerance, the second wind phenomenon, and high serum creatine kinase activity. Here, we recapitulate PYGM mutations in the population responsible for this disease. Traditionally, McArdle disease has been considered a metabolic myopathy caused by the lack of expression of the muscle isoform of the glycogen phosphorylase (PYGM). However, recent findings challenge this view, since it has been shown that PYGM is present in other tissues than the skeletal muscle. We review the latest studies about the molecular mechanism involved in glycogen phosphorylase activity regulation. Further, we summarize the expression and functional significance of PYGM in other tissues than skeletal muscle both in health and McArdle disease. Furthermore, we examine the different animal models that have served as the knowledge base for better understanding of McArdle disease. Finally, we give an overview of the latest state-of-the-art clinical trials currently being carried out and present an updated view of the current therapies.

Molecular Imaging of Retinoic Acids in Live Cells Using Single-Chain Bioluminescence Probes

Retinoic acid (RA) is a key metabolite necessary for embryonic development and differentiation in vertebrates. We demonstrate the utility of genetically encoded, ligand-activatable single-chain bioluminescence probes for detecting RAs from different biological sources. We examined 13 different molecular designs to identify an efficient single-chain probe that can quantify RA with significant sensitivity. The optimal probe consisted of four components: the N- and C-terminal fragments of artificial luciferase variant-16 (ALuc16), the ligand binding domain of retinoic acid receptor α (RARα LBD), and an LXXLL interaction motif. This probe showed a 5.2-fold greater bioluminescence intensity in response to RA when compared to the vehicle control in live mammalian cells. The probe was highly selective to all-trans-RA (at-RA), and highly sensitive in determining at-RA levels in cells derived from tumor xenografts created using MDA-MB-231 cells engineered to stably express the probe. We also detected RA levels in serum and cerebrospinal fluid. Using this probe, the detection limit for at-RA was ∼10^-9.5 M, with a linear range of two orders. We present a highly useful technique to quantitatively image endogenous at-RA levels in live mammalian cells expressing novel single-chain bioluminescence probes.

O-GlcNAcylation of GLI transcription factors in hyperglycemic conditions augments Hedgehog activity

Modification of proteins by O-linked β-N-acetylglucosamine (O-GlcNAc) promotes tumor cell survival, proliferation, epigenetic changes, angiogenesis, invasion, and metastasis. Here we demonstrate that in conditions of elevated glucose, there is increased expression of key drug resistance proteins (ABCB1, ABCG2, ERCC1, and XRCC1), all of which are regulated by the Hedgehog pathway. In elevated glucose conditions, we determined that the Hedgehog pathway transcription factors, GLI1 and GLI2, are modified by O-GlcNAcylation. This modification functionally enhanced their transcriptional activity. The activity of GLI was enhanced when O-GlcNAcase was inhibited, while inhibiting O-GlcNAc transferase caused a decrease in GLI activity. The metabolic impact of hyperglycemic conditions impinges on maintaining PKM2 in the less active state that facilitates the availability of glycolytic intermediates for biosynthetic pathways. Interestingly, under elevated glucose conditions, PKM2 directly influenced GLI activity. Specifically, abrogating PKM2 expression caused a significant decline in GLI activity and expression of drug resistance proteins. Cumulatively, our results suggest that elevated glucose conditions upregulate chemoresistance through elevated transcriptional activity of the Hedgehog/GLI pathway. Interfering in O-GlcNAcylation of the GLI transcription factors may be a novel target in controlling cancer progression and drug resistance of breast cancer.

An ultra-low thiourea catalyzed strain-release glycosylation and a multicatalytic diversification strategy

The utility of thiourea catalysis in selective glycosylation strategies has gained significant momentum lately due to its versatility in hydrogen bonding or anionic recognition activation modes. The use of these non-covalent interactions constitute a powerful means to construct glycosidic linkages as it mimics physiologically occurring glycosyltransferases. However, glycosyl donor activation through the currently employed catalysts is moderate such that, in general, catalyst loadings are rather high in these transformations. In addition, thiourea catalysis has not been well explored for the synthesis of furanosides. Herein, we demonstrate an ultra-low loadings stereoselective and stereospecific thiourea catalyzed strain-release furanosylation and pyranosylation strategy. Our ultra-low organocatalyzed furanosylation enables a multicatalytic strategy, which opens up a unique avenue towards rapid diversification of synthetic glycosides. In-situ NMR monitoring unravel insights into unknown reaction intermediates and initial rate kinetic studies reveal a plausible synergistic hydrogen bonding/Brønsted acid activation mode.

Non-covalent glycosyl donor activation often requires high organocatalyst loadings. Here, the authors demonstrate that strain-release glycosylations can take place at very low thiourea catalyst loadings. In addition, the authors developed a one-pot multicatalytic strategy that can diversify glycosides rapidly.

Chemoenzymatic Methods for the Synthesis of Glycoproteins

Glycosylation is one of the most prevalent posttranslational modifications that profoundly affects the structure and functions of proteins in a wide variety of biological recognition events. However, the structural complexity and heterogeneity of glycoproteins, usually resulting from the variations of glycan components and/or the sites of glycosylation, often complicates detailed structure-function relationship studies and hampers the therapeutic applications of glycoproteins. To address these challenges, various chemical and biological strategies have been developed for producing glycan-defined homogeneous glycoproteins. This review highlights recent advances in the development of chemoenzymatic methods for synthesizing homogeneous glycoproteins, including the generation of various glycosynthases for synthetic purposes, endoglycosidase-catalyzed glycoprotein synthesis and glycan remodeling, and direct enzymatic glycosylation of polypeptides and proteins. The scope, limitation, and future directions of each method are discussed.

Augmented O-GlcNAcylation alleviates inflammation-mediated colon carcinogenesis via suppression of acute inflammation

Colon cancer prevalence is high worldwide. O-GlcNAcylation has been associated with tumor growth in various tissues, including the colon; however, its link to carcinogenesis is not fully understood. We investigated the association of O-GlcNAcylation with colon carcinogenesis using a 1,2-dimethylhydrazine/dextran sodium sulfate-induced colon carcinogenesis model in wild type and O-GlcNAc transferase-transgenic (Ogt-Tg) mice. The incidence of colon cancer was significantly lower in Ogt-Tg than in wild type mice. The colonic length was not shortened in Ogt-Tg mice, and NF-κB p65 phosphorylation was strongly suppressed, indicating that reduction of inflammation might be related to the alleviation of colon carcinogenesis. Dextran sodium sulfate-induced acute colitis mice were used to evaluate the effect of O-GlcNAcylation on inflammation at the maximal inflammation period. In Ogt-Tg mice, NF-κB p65 phosphorylation and interleukin-1β mRNA expression were suppressed. Histochemical staining demonstrated shedding of colon epithelial cells in wild type mice a few days after dextran sodium sulfate treatment, whereas they remained essentially intact in Ogt-Tg mice. There were no significant differences on histochemical staining in the remaining epithelia between groups. These data suggest that O-GlcNAcylation could prevent colon carcinogenesis through reducing acute maximum inflammation, suggesting modulation of O-GlcNAcylation as a novel therapeutic option.

Control of CREB expression in tumors: from molecular mechanisms and signal transduction pathways to therapeutic target

The cyclic AMP response element binding (CREB) protein has pleiotropic activities in physiologic processes. Due to its central position downstream of many growth signaling pathways CREB has the ability to influence cell survival, growth and differentiation of normal, but also of tumor cells suggesting an oncogenic potential of CREB. Indeed, increased CREB expression and activation is associated with tumor progression, chemotherapy resistance and reduced patients' survival. We summarize here the different cellular functions of CREB in tumors of distinct histology as well as its use as potential prognostic marker. In addition, the underlying molecular mechanisms to achieve constitutive activation of CREB including structural alterations, such as gene amplification and chromosomal translocation, and deregulation, which could occur at the transcriptional, post-transcriptional and post-translational level, will be described. Since downregulation of CREB by different strategies resulted in inhibition of cell proliferation, invasion and induction of apoptosis, the role of CREB as a promising target for cancer therapy will be also discussed.

Noninvasive liquid diet delivery of stable isotopes into mouse models for deep metabolic network tracing

Delivering isotopic tracers for metabolic studies in rodents without overt stress is challenging. Current methods achieve low label enrichment in proteins and lipids. Here, we report noninvasive introduction of ¹³C₆-glucose via a stress-free, ad libitum liquid diet. Using NMR and ion chromatography-mass spectrometry, we quantify extensive ¹³C enrichment in products of glycolysis, the Krebs cycle, the pentose phosphate pathway, nucleobases, UDP-sugars, glycogen, lipids, and proteins in mouse tissues during 12 to 48 h of ¹³C₆-glucose feeding. Applying this approach to patient-derived lung tumor xenografts (PDTX), we show that the liver supplies glucose-derived Gln via the blood to the PDTX to fuel Glu and glutathione synthesis while gluconeogenesis occurs in the PDTX. Comparison of PDTX with ex vivo tumor cultures and arsenic-transformed lung cells versus xenografts reveals differential glucose metabolism that could reflect distinct tumor microenvironment. We further found differences in glucose metabolism between the primary PDTX and distant lymph node metastases.

Genetic Variation and Its Reflection on Posttranslational Modifications in Frequency Clock and Mating Type a-1 Proteins in Sordaria fimicola

Posttranslational modifications (PTMs) occur in all essential proteins taking command of their functions. There are many domains inside proteins where modifications take place on side-chains of amino acids through various enzymes to generate different species of proteins. In this manuscript we have, for the first time, predicted posttranslational modifications of frequency clock and mating type a-1 proteins in Sordaria fimicola collected from different sites to see the effect of environment on proteins or various amino acids pickings and their ultimate impact on consensus sequences present in mating type proteins using bioinformatics tools. Furthermore, we have also measured and walked through genomic DNA of various Sordaria strains to determine genetic diversity by genotyping the short sequence repeats (SSRs) of wild strains of S. fimicola collected from contrasting environments of two opposing slopes (harsh and xeric south facing slope and mild north facing slope) of Evolution Canyon (EC), Israel. Based on the whole genome sequence of S. macrospora, we targeted 20 genomic regions in S. fimicola which contain short sequence repeats (SSRs). Our data revealed genetic variations in strains from south facing slope and these findings assist in the hypothesis that genetic variations caused by stressful environments lead to evolution.

The New Chemical Reporter 6-Alkynyl-6-deoxy-GlcNAc Reveals O-GlcNAc Modification of the Apoptotic Caspases That Can Block the Cleavage/Activation of Caspase-8

O-GlcNAc modification (O-GlcNAcylation) is required for survival in mammalian cells. Genetic and biochemical experiments have found that increased modification inhibits apoptosis in tissues and cell culture and that lowering O-GlcNAcylation induces cell death. However, the molecular mechanisms by which O-GlcNAcylation might inhibit apoptosis are still being elucidated. Here, we first synthesize a new metabolic chemical reporter, 6-Alkynyl-6-deoxy-GlcNAc (6AlkGlcNAc), for the identification of O-GlcNAc-modified proteins. Subsequent characterization of 6AlkGlcNAc shows that this probe is selectively incorporated into O-GlcNAcylated proteins over cell-surface glycoproteins. Using this probe, we discover that the apoptotic caspases are O-GlcNAcylated, which we confirmed using other techniques, raising the possibility that the modification affects their biochemistry. We then demonstrate that changes in the global levels of O-GlcNAcylation result in a converse change in the kinetics of caspase-8 activation during apoptosis. Finally, we show that caspase-8 is modified at residues that can block its cleavage/activation. Our results provide the first evidence that the caspases may be directly affected by O-GlcNAcylation as a potential antiapoptotic mechanism.

O-GlcNAc modification inhibits the calpain-mediated cleavage of α-synuclein

The major protein associated with Parkinson's disease (PD) is α-synuclein, as it can form toxic amyloid-aggregates that are a hallmark of many neurodegenerative diseases. α-Synuclein is a substrate for several different posttranslational modifications (PTMs) that have the potential to affect its biological functions and/or aggregation. However, the biophysical effects of many of these modifications remain to be established. One such modification is the addition of the monosaccharide N-acetyl-glucosamine, O-GlcNAc, which has been found on several α-synuclein serine and threonine residues in vivo. We have previously used synthetic protein chemistry to generate α-synuclein bearing two of these physiologically relevant O-GlcNAcylation events at threonine 72 and serine 87 and demonstrated that both of these modifications inhibit α-synuclein aggregation. Here, we use the same synthetic protein methodology to demonstrate that these same O-GlcNAc modifications also inhibit the cleavage of α-synuclein by the protease calpain. This further supports a role for O-GlcNAcylation in the modulation of α-synuclein biology, as proteolysis has been shown to potentially affect both protein aggregation and degradation.

The Small Molecule 2-Azido-2-deoxy-glucose Is a Metabolic Chemical Reporter of O-GlcNAc Modifications in Mammalian Cells, Revealing an Unexpected Promiscuity of O-GlcNAc Transferase

Glycans can be directly labeled using unnatural monosaccharide analogs, termed metabolic chemical reporters (MCRs). These compounds enable the secondary visualization and identification of glycoproteins by taking advantage of bioorthogonal reactions. Most widely used MCRs have azides or alkynes at the 2-N-acetyl position but are not selective for one class of glycoprotein over others. To address this limitation, we are exploring additional MCRs that have bioorthogonal functionality at other positions. Here, we report the characterization of 2-azido-2-deoxy-glucose (2AzGlc). We find that 2AzGlc selectively labels intracellular O-GlcNAc modifications, which further supports a somewhat unexpected, structural flexibility in this pathway. In contrast to the endogenous modification N-acetyl-glucosamine (GlcNAc), we find that 2AzGlc is not dynamically removed from protein substrates and that treatment with higher concentrations of per-acetylated 2AzGlc is toxic to cells. Finally, we demonstrate that this toxicity is an inherent property of the small-molecule, as removal of the 6-acetyl-group renders the corresponding reporter nontoxic but still results in protein labeling.

Identification and characterization of a missense mutation in the O-linked β-N-acetylglucosamine (O-GlcNAc) transferase gene that segregates with X-linked intellectual disability

O-GlcNAc is a regulatory post-translational modification of nucleocytoplasmic proteins that has been implicated in multiple biological processes, including transcription. In humans, single genes encode enzymes for its attachment (O-GlcNAc transferase (OGT)) and removal (O-GlcNAcase (OGA)). An X-chromosome exome screen identified a missense mutation, which encodes an amino acid in the tetratricopeptide repeat, in OGT (759G>T (p.L254F)) that segregates with X-linked intellectual disability (XLID) in an affected family. A decrease in steady-state OGT protein levels was observed in isolated lymphoblastoid cell lines from affected individuals, consistent with molecular modeling experiments. Recombinant expression of L254F-OGT demonstrated that the enzyme is active as both a glycosyltransferase and an HCF-1 protease. Despite the reduction in OGT levels seen in the L254F-OGT individual cells, we observed that steady-state global O-GlcNAc levels remained grossly unaltered. Surprisingly, lymphoblastoids from affected individuals displayed a marked decrease in steady-state OGA protein and mRNA levels. We observed an enrichment of the OGT-containing transcriptional repressor complex mSin3A-HDAC1 at the proximal promoter region of OGA and correspondingly decreased OGA promoter activity in affected cells. Global transcriptome analysis of L254F-OGT lymphoblastoids compared with controls revealed a small subset of genes that are differentially expressed. Thus, we have begun to unravel the molecular consequences of the 759G>T (p.L254F) mutation in OGT that uncovered a compensation mechanism, albeit imperfect, given the phenotype of affected individuals, to maintain steady-state O-GlcNAc levels. Thus, a single amino acid substitution in the regulatory domain (the tetratricopeptide repeat domain) of OGT, which catalyzes the O-GlcNAc post-translational modification of nuclear and cytosolic proteins, appears causal for XLID.

[O-GlcNAc glycosylation influences the biological behaviors and etoposide-induced apoptosis of Nalm-6 cells]

目的

研究O连接的N-乙酰葡萄糖胺（O-GlcNAc）糖基化及乙酰氨基葡萄糖转移酶（OGT）对Nalm-6细胞生物学行为及对依托泊苷（Vp16）诱导凋亡的影响。

方法

利用OGT抑制剂Alloxan构建低O-GlcNAc修饰的Nalm-6细胞模型，CCK-8法检测Alloxan对细胞增殖的影响，流式细胞术检测Alloxan对细胞凋亡及细胞周期的影响；以不同浓度的Vp16处理Nalm-6细胞12 h，Western blot检测O-GlcNAc糖基化修饰程度及OGT表达量的变化；以Alloxan处理Nalm-6细胞24 h后再加入Vp16（5 µg/ml）处理12 h，应用流式细胞术检测不同组别细胞凋亡，Western blot检测凋亡相关蛋白Bax和Bcl-2的表达情况。

结果

随着Vp16浓度的增加，Nalm-6细胞O-GlcNAc修饰及OGT表达均逐渐上调（P<0.05）；Alloxan可抑制Nalm-6细胞增殖，诱发Nalm-6细胞凋亡[（15.190±2.539）%对（21.910±4.105）%，P=0.007]，阻滞细胞周期[G₁期：（43.534±4.453）%对（57.322±6.091）%，P=0.003；S期：（50.747±5.937）%对（37.201±4.661）%，P=0.001]；Alloxan可抑制Vp16诱导的Nalm-6细胞凋亡[（75.195±13.845）%对（52.741±10.815）%，P=0.011]，并伴随Bax表达下调（5.496±1.998对2.950±0.703，P=0.015）、Bcl-2表达上调（0.454±0.125对0.803±0.223，P=0.013）。

结论

通过抑制OGT而改变Nalm-6细胞O-GlcNAc修饰程度可影响其增殖、凋亡、改变细胞周期并抑制Vp16诱导的细胞凋亡。

Harnessing cancer cell metabolism for theranostic applications using metabolic glycoengineering of sialic acid in breast cancer as a pioneering example

Abnormal cell surface display of sialic acids - a family of unusual 9-carbon sugars - is widely recognized as distinguishing feature of many types of cancer. Sialoglycans, however, typically cannot be identified with sufficiently high reproducibility and sensitivity to serve as clinically accepted biomarkers and similarly, almost all efforts to exploit cancer-specific differences in sialylation signatures for therapy remain in early stage development. In this report we provide an overview of important facets of glycosylation that contribute to cancer in general with a focus on breast cancer as an example of malignant disease characterized by aberrant sialylation. We then describe how cancer cells experience nutrient deprivation during oncogenesis and discuss how the resulting metabolic reprogramming, which endows breast cancer cells with the ability to obtain nutrients during scarcity, constitutes an "Achilles' heel" that we believe can be exploited by metabolic glycoengineering (MGE) strategies to develop new diagnostic methods and therapeutic approaches. In particular, we hypothesize that adaptations made by breast cancer cells that allow them to efficiently scavenge sialic acid during times of nutrient deprivation renders them vulnerable to MGE, which refers to the use of exogenously-supplied, non-natural monosaccharide analogues to modulate targeted aspects of glycosylation in living cells and animals. In specific, once non-natural sialosides are incorporated into the cancer "sialome" they can be exploited as epitopes for immunotherapy or as chemical tags for targeted delivery of imaging or therapeutic agents selectively to tumors.

Hyper-O-GlcNAcylation of YB-1 affects Ser102 phosphorylation and promotes cell proliferation in hepatocellular carcinoma

As an essential post-translational modification, O-GlcNAcylation has been thought to be able to modulate various nuclear and cytoplasmic proteins and is emerging as a key regulator of multiple biological processes, such as transcription, cell growth, signal transduction, and cell motility. Recently, authoritative glycomics analyses have reported extensive crosstalk between O-GlcNAcylation and phosphorylation, which always dynamically interplay with each other and regulate signaling, transcription, and other cellular processes. Also, plentiful studies have shown close correlation between YB-1 phosphorylation and tumorigenesis. Therefore, our study aimed to determine whether YB-1 was O-GlcNAc modified and whether such modification could interact with its phosphorylation during the process of HCC development. Western blot and immunohistochemistry were firstly conducted to reveal obvious up-regulation of YB-1, OGT and O-GlcNAc modification in HCC tissues. What is more, not only YB-1 was identified to be O-GlcNAcylated but hyper-O-GlcNAcylation was demonstrated to facilitate HCC cell proliferation in a YB-1 dependent manner. Moreover, we detected four specific O-GlcNAc sites and confirmed T126A to be the most effective mutant in HCC cell proliferation via close O-GlcNAcylation-phosphorylation interaction. Even more interestingly, we discovered that T126A-induced HCC cell retardation and subdued transcriptional activity of YB-1 could be partially reversed by T126A/S102E mutant. From all above, it is not difficult to find that glycosylated-YB-1 mainly enhanced cell proliferation through congenerous actions with YB-1 phosphorylation and thus played indispensable roles in fine-tuning cell proliferation and procession of HCC.

O-Linked β-N-acetylglucosamine (O-GlcNAc) Acts as a Glucose Sensor to Epigenetically Regulate the Insulin Gene in Pancreatic Beta Cells

The post-translational protein modification O-linked β-N-acetylglucosamine (O-GlcNAc) is a proposed nutrient sensor that has been shown to regulate multiple biological pathways. This dynamic and inducible enzymatic modification to intracellular proteins utilizes the end product of the nutrient sensing hexosamine biosynthetic pathway, UDP-GlcNAc, as its substrate donor. Type II diabetic patients have elevated O-GlcNAc-modified proteins within pancreatic beta cells due to chronic hyperglycemia-induced glucose overload, but a molecular role for O-GlcNAc within beta cells remains unclear. Using directed pharmacological approaches in the mouse insulinoma-6 (Min6) cell line, we demonstrate that elevating nuclear O-GlcNAc increases intracellular insulin levels and preserves glucose-stimulated insulin secretion during chronic hyperglycemia. The molecular mechanism for these observed changes appears to be, at least in part, due to elevated O-GlcNAc-dependent increases in Ins1 and Ins2 mRNA levels via elevations in histone H3 transcriptional activation marks. Furthermore, RNA deep sequencing reveals that this mechanism of altered gene transcription is restricted and that the majority of genes regulated by elevated O-GlcNAc levels are similarly regulated by a shift from euglycemic to hyperglycemic conditions. These findings implicate the O-GlcNAc modification as a potential mechanism for hyperglycemic-regulated gene expression in the beta cell.

Hexosamine-Induced TGF-β Signaling and Osteogenic Differentiation of Dental Pulp Stem Cells Are Dependent on N-Acetylglucosaminyltransferase V

Glycans of cell surface glycoproteins are involved in the regulation of cell migration, growth, and differentiation. N-acetyl-glucosaminyltransferase V (GnT-V) transfers N-acetyl-d-glucosamine to form β1,6-branched N-glycans, thus playing a crucial role in the biosynthesis of glycoproteins. This study reveals the distinct expression of GnT-V in STRO-1 and CD-146 double-positive dental pulp stem cells (DPSCs). Furthermore, we investigated three types of hexosamines and their N-acetyl derivatives for possible effects on the osteogenic differentiation potential of DPSCs. Our results showed that exogenous d-glucosamine (GlcN), N-acetyl-d-glucosamine (GlcNAc), d-mannosamine (ManN), and acetyl-d-mannosamine (ManNAc) promoted DPSCs' early osteogenic differentiation in the absence of osteogenic supplements, but d-galactosamine (GalN) or N-acetyl-galactosamine (GalNAc) did not. Effects include the increased level of TGF-β receptor type I, activation of TGF-β signaling, and increased mRNA expression of osteogenic differentiation marker genes. The hexosamine-treated DPSCs showed an increased mineralized matrix deposition in the presence of osteogenic supplements. Moreover, the level of TGF-β receptor type I and early osteogenic differentiation were abolished in the DPSCs transfected with siRNA for GnT-V knockdown. These results suggest that GnT-V plays a critical role in the hexosamine-induced activation of TGF-β signaling and subsequent osteogenic differentiation of DPSCs.

Proteomic analysis of O-GlcNAcylated proteins in invasive ductal breast carcinomas with and without lymph node metastasis

The potential role of protein O-GlcNAcylation in cancer has been studied extensively, and the spread of cancer cells to regional lymph nodes is the first step in the dissemination of breast cancer. However, the correlation between O-GlcNAcylation and lymphatic metastasis in breast cancer remains elusive. In this study, we demonstrated that the overall O-GlcNAcylation as well as O-GlcNAc transferase (OGT) tends to decrease in response to the augmentation of lymph node metastasis (LNM) in invasive ductal breast carcinomas (IDCs). Although accumulating evidence indicates that individual O-GlcNAcylation may be important in the pathogenesis of breast cancer, O-GlcNAcylated proteins in IDCs are still largely unexplored. Herein, O-GlcNAcylated proteins of IDCs were chemo-enzymatically enriched and identified via liquid chromatography combined with tandem mass spectrometry. In total, 155 O-GlcNAcylated proteins were determined, of which 41 were only observed in LNM tissues, while 40 were unique in non-LNM samples. Gene ontology analysis showed that O-GlcNAc is primarily a nucleocytoplasmic post-translational modification, and most enriched functional terms were related to cancer development in both metastatic and non-metastatic IDCs. Moreover, several O-GlcNAcylated proteins involved in glycolysis and its accessory pathway were identified from LNM and non-LNM groups, respectively. These results indicate that the O-GlcNAcylation statuses of individual proteins were independent of the overall O-GlcNAcylation levels of metastatic and non-metastatic IDCs. Aberrant O-GlcNAc modification of these proteins might be associated with LNM progression.