Structures and mechanism of human glycosyltransferase β1,3-N-acetylglucosaminyltransferase 2 (B3GNT2), an important player in immune homeostasis

A scan of pleiotropic immune mediated disease genes identifies novel determinants of baseline FVIII inhibitor status in hemophilia A

Hemophilia-A (HA) is the X-linked bleeding disorder caused by heterogeneous factor (F)VIII gene (F8)-mutations and deficiencies in plasma-FVIII-activity that prevent intrinsic-pathway mediated coagulation-amplification. Severe-HA patients (HAPs) require life-long infusions of therapeutic-FVIII-proteins (tFVIIIs) but ~30% develop neutralizing-tFVIII-antibodies called "FVIII-inhibitors (FEIs)". We investigated the genetics underlying the variable risk of FEI-development in 450 North American HAPs (206 and 244 respectively self-reporting black-African- or white-European-ancestry) by analyzing the genotypes of single-nucleotide-variations (SNVs) in candidate immune-mediated-disease (IMD)-genes using a binary linear-mixed model of genetic association with baseline-FEI-status, the dependent variable, while simultaneously accounting for their genetic relationships and heterogeneous-F8-mutations to prevent the statistical problem of non-independence. We a priori selected gene-centric-association-scans of pleiotropic-IMD-genes implicated in the development of either ≥2 autoimmune-/autoinflammatory-disorders (AADs) or FEIs and ≥1 AAD. We found that baseline-FEI-status was significantly associated with NOS2A (rs117382854; p = 3.2 × 10-6) and B3GNT2 (rs10176009; p = 5.1 × 10-6)-pleiotropic-IMD-genes known previously to function in anti-microbial-/-tumoral-immunity but not in the development of FEIs-and confirmed associations with CTLA4 (rs231780; p = 2.2 × 10-5). We also found that baseline-FEI-status has a substantial heritability (~55%) that involves (i) a F8-mutation-specific component of ~8%, (ii) an additive-genetic contribution from SNVs in IMD-genes of ~47%, and (iii) race, which is a significant determinant independent of F8-mutation-types and non-F8-genetics.

Two-step Production Method for Lacto-N-Triose II via Cell-Coupled Biocatalytic Strategy

Lacto-N-triose II (LNT II) represents a significant neutral human milk oligosaccharide (HMO) that functions as a fundamental structural framework for the synthesis of more complex HMOs. In this study, we utilize GlcNAc and lactose as substrates, employing a whole-cell catalytic approach for the synthesis of LNT II. First, we have identified and successfully expressed three genes associated with the production of LNT II: Nahk, EcGlmU, and LgtA, synthesized LNT II through a whole-cell catalytic system utilizing multistrain coupling. Then, to further enhance the yield, we incorporated yeast cells for energy regeneration, employed coexpression strategies to minimize cell density, following a series of systematic optimizations resulting in a 7-fold increase in LNT II production. Finally, a two-step catalytic process was conducted in a 5L bioreactor, and the maximum LNT II production reached 52.34 g/L with a conversion rate of lactose 95.95%.

Structure-Based Mechanism and Specificity of Human Galactosyltransferase β3GalT5

Human β1,3-galactosyltransferase 5 (β3GalT5) is a key enzyme involved in the synthesis of glycans on glycoproteins and glycolipids that are associated with various important biological functions, especially tumor malignancy and cancer progression, and has been considered as a promising target for development of anticancer agents. In this study, we determined the X-ray structures of β3GalT5 in complex with the stable donor analogue UDP-2-fluorogalactose or the native donor substrate UDP-galactose (UDP-Gal) and several glycan acceptors at different reaction steps. Based on the structures obtained from our experiments, β3GalT5 catalyzes the transfer of galactose from UDP-Gal to a broad spectrum of glycan acceptors with an SN2-like mechanism; however, in the absence of a glycan acceptor, UDP-Gal is slowly converted to UDP and two other products, one is galactose through an SN2-like mechanism with water as an acceptor and the other is an oxocarbenium-like product, presumably through an SN1-like mechanisms. The structure, mechanism, and specificity of β3GalT5 presented in this study advance our understanding of enzymatic glycosylation and provide valuable insights for application to glycan synthesis and drug design targeting β3GalT5-associated cancer.

The glycosyltransferase ST3GAL4 drives immune evasion in acute myeloid leukemia by synthesizing ligands for the glyco-immune checkpoint receptor Siglec-9

Immunotherapy has demonstrated promise as a treatment for acute myeloid leukemia (AML). However, there is still an urgent need to identify new molecules that inhibit the immune response to AML. Most prior research in this area has focused on protein-protein interaction interfaces. While carbohydrates also regulate immune recognition, the role of cell-surface glycans in driving AML immune evasion is comparatively understudied. The Siglecs, for example, are an important family of inhibitory, glycan-binding signaling receptors that have emerged as prime targets for cancer immunotherapy in recent years. In this study, we find that AML cells express ligands for the receptor Siglec-9 at high levels. Integrated CRISPR genomic screening and clinical bioinformatic analysis identified ST3GAL4 as a potential driver of Siglec-9 ligand expression in AML. Depletion of ST3GAL4 by CRISPR-Cas9 knockout (KO) dramatically reduced the expression of Siglec-9 ligands in AML cells. Mass spectrometry analysis of cell-surface glycosylation in ST3GAL4 KO cells revealed that Siglec-9 primarily binds N-linked sialoglycans on these cell types. Finally, we found that ST3GAL4 KO enhanced the sensitivity of AML cells to phagocytosis by Siglec-9-expressing macrophages. This work reveals a novel axis of immune evasion and implicates ST3GAL4 as a possible target for  immunotherapy in AML.

Identifying prioritization of therapeutic targets for ankylosing spondylitis: a multi-omics Mendelian randomization study

BACKGROUND

To investigate the associations of methylation, expression, and protein quantitative trait loci (mQTL, eQTL, and pQTL) with ankylosing spondylitis (AS) and find out genetically supported drug targets for AS.

METHODS

The summary-data-based Mendelian randomization (SMR) and Bayesian co-localization analysis were used to assess the potential causality between AS and relevant genes. The GWAS data obtained from the International Genetics of Ankylosing Spondylitis Consortium (IGAS) were set as the discovery stage, and the FinnGen and UK Biobank databases were used to replicate the analysis as an external validation. We further integrated the multi-omics results to screen overlapped genes at different levels. The protein-protein interaction (PPI) network and enrichment analyses were used to explore the biological effect of SMR-identified genes on AS. Drug prediction and molecular docking were used to validate the medicinal value of candidate drug targets.

RESULTS

Based on the results of multi-omics evidence screening, we identified potential associations of TNFRSF1A, B3GNT2, ERAP1, and FCGR2A with AS at different regulatory levels. At the protein level, AIF1, TNXB, APOM, and B3GNT2 were found to be negatively associated with AS risk, whereas higher levels of FCGR2A, FCGR2B, IL12B, TNFRSF1A, and ERAP1 were associated with an increased risk of AS. The bioinformatics analyses showed that the SMR-identified genes were mainly involved in immune response. Molecular docking results displayed stable binding between predicted candidate drugs and these aforementioned proteins.

CONCLUSION

Our study found four AS-associated genes with multi-omics evidence and nine promising drug targets for AS, which may contribute to the understanding of the genetic mechanisms of AS and provide innovative perspectives into targeted therapy for AS.

Substrate binding and catalytic mechanism of UDP-α-D-galactofuranose: β-galactofuranoside β-(1→5)-galactofuranosyltransferase GfsA

UDP-α-D-galactofuranose (UDP-Galf): β-galactofuranoside β-(1→5)-galactofuranosyltransferase, known as GfsA, is essential in synthesizing β-(1→5)-galactofuranosyl oligosaccharides that are incorporated into the cell wall of pathogenic fungi. This study analyzed the structure and function of GfsA from Aspergillus fumigatus. To provide crucial insights into the catalytic mechanism and substrate recognition, the complex structure was elucidated with manganese (Mn2+), a donor substrate product (UDP), and an acceptor sugar molecule (β-galactofuranose). In addition to the typical GT-A fold domain, GfsA has a unique domain formed by the N and C termini. The former interacts with the GT-A of another GfsA, forming a dimer. The active center that contains Mn2+, UDP, and galactofuranose forms a groove structure that is highly conserved in the GfsA of Pezizomycotina fungi. Enzymatic assays using site-directed mutants were conducted to determine the roles of specific active-site residues in the enzymatic activity of GfsA. The predicted enzyme-substrate complex model containing UDP-Galf characterized a specific β-galactofuranosyltransfer mechanism to the 5'-OH of β-galactofuranose. Overall, the structure of GfsA in pathogenic fungi provides insights into the complex glycan biosynthetic processes of fungal pathogenesis and may inform the development of novel antifungal therapies.

Glycosphingolipids: from metabolism to chemoenzymatic total synthesis

GSLs are the major glycolipids in vertebrates and mediate many key biological processes from intercellular recognition to cis regulation of signal transduction. The fast-expanding field of glycobiology has led to a growing demand for diverse and structurally defined GSLs, and enzymatic GSL synthesis is developing rapidly in accordance. This article provides an overview of natural GSL biosynthetic pathways and surveys the bacterial enzymes applied to GSL synthesis and recent progress in synthesis strategies. By correlating these three areas, this article aims to define the gaps between GSL biosynthesis and chemoenzymatic synthesis and evaluate the opportunities for harnessing natural forces to access GSLs efficiently.

Protein N-glycans in Healthy and Sclerotic Glomeruli in Diabetic Kidney Disease

BACKGROUND

Diabetes is expected to directly impact renal glycosylation, yet to date, there has not been a comprehensive evaluation of alterations in N-glycan composition in the glomeruli of patients with diabetic kidney disease (DKD).

METHODS

We used untargeted mass spectrometry imaging to identify N-glycan structures in healthy and sclerotic glomeruli in FFPE sections from needle biopsies of five patients with DKD and three healthy kidney samples. Regional proteomics was performed on glomeruli from additional biopsies from the same patients to compare the abundances of enzymes involved in glycosylation. Secondary analysis of single nuclei transcriptomics (snRNAseq) data was used to inform on transcript levels of glycosylation machinery in different cell types and states.

RESULTS

We detected 120 N-glycans, and among them identified twelve of these protein post-translated modifications that were significantly increased in glomeruli. All glomeruli-specific N-glycans contained an N-acetyllactosamine (LacNAc) epitope. Five N-glycan structures were highly discriminant between sclerotic and healthy glomeruli. Sclerotic glomeruli had an additional set of glycans lacking fucose linked to their core, and they did not show tetra-antennary structures that are common in healthy glomeruli. Orthogonal omics analyses revealed lower protein abundance and lower gene expression involved in synthesizing fucosylated and branched N-glycans in sclerotic podocytes. In snRNAseq and regional proteomics analyses, we observed that genes and/or proteins involved in sialylation and LacNAc synthesis were also downregulated in DKD glomeruli, but this alteration remained undetectable by our spatial N-glycomics assay.

CONCLUSIONS

Integrative spatial glycomics, proteomics, and transcriptomics revealed protein N-glycosylation characteristic of sclerotic glomeruli in DKD.

A genetic association study of circulating coagulation factor VIII and von Willebrand factor levels

ABSTRACT

Coagulation factor VIII (FVIII) and its carrier protein von Willebrand factor (VWF) are critical to coagulation and platelet aggregation. We leveraged whole-genome sequence data from the Trans-Omics for Precision Medicine (TOPMed) program along with TOPMed-based imputation of genotypes in additional samples to identify genetic associations with circulating FVIII and VWF levels in a single-variant meta-analysis, including up to 45 289 participants. Gene-based aggregate tests were implemented in TOPMed. We identified 3 candidate causal genes and tested their functional effect on FVIII release from human liver endothelial cells (HLECs) and VWF release from human umbilical vein endothelial cells. Mendelian randomization was also performed to provide evidence for causal associations of FVIII and VWF with thrombotic outcomes. We identified associations (P < 5 × 10-9) at 7 new loci for FVIII (ST3GAL4, CLEC4M, B3GNT2, ASGR1, F12, KNG1, and TREM1/NCR2) and 1 for VWF (B3GNT2). VWF, ABO, and STAB2 were associated with FVIII and VWF in gene-based analyses. Multiphenotype analysis of FVIII and VWF identified another 3 new loci, including PDIA3. Silencing of B3GNT2 and the previously reported CD36 gene decreased release of FVIII by HLECs, whereas silencing of B3GNT2, CD36, and PDIA3 decreased release of VWF by HVECs. Mendelian randomization supports causal association of higher FVIII and VWF with increased risk of thrombotic outcomes. Seven new loci were identified for FVIII and 1 for VWF, with evidence supporting causal associations of FVIII and VWF with thrombotic outcomes. B3GNT2, CD36, and PDIA3 modulate the release of FVIII and/or VWF in vitro.

Impacts of β-1, 3-N-acetylglucosaminyltransferases (B3GNTs) in human diseases

Glycosylation modification of proteins is a common post-translational modification that exists in various organisms and has rich biological functions. It is usually catalyzed by multiple glycosyltransferases located in the Golgi apparatus. β-1,3-N-acetylglucosaminyltransferases (B3GNTs) are members of the glycosyltransferases and have been found to be involved in the occurrence and development of a variety of diseases including autoimmunity diseases, cancers, neurodevelopment, musculoskeletal system, and metabolic diseases. The functions of B3GNTs represent the glycosylation of proteins is a crucial and frequently life-threatening step in progression of most diseases. In this review, we give an overview about the roles of B3GNTs in tumor, nervous system, musculoskeletal and metabolic diseases, describing the recent results about B3GNTs, in order to provide a research direction and exploration value for the prevention, diagnosis and treatment of these diseases.

Glyco-Engineering Cell Surfaces by Exo-Enzymatic Installation of GlcNAz and LacNAz Motifs

Exo-enzymatic glyco-engineering of cell-surface glycoconjugates enables the selective display of well-defined glyco-motifs bearing bioorthogonal functional groups, which can be used to study glycans and their interactions with glycan-binding proteins. In recent years, strategies to edit cellular glycans by installing monosaccharides and their derivatives using glycosyltransferase enzymes have rapidly expanded. However, analogous methods to introduce chemical reporter-functionalized type 2 LacNAc motifs have not been reported. Herein, we report the chemo-enzymatic synthesis of unnatural UDP-GlcNAc and UDP-GalNAc nucleotide-sugars bearing azide, alkyne, and diazirine functionalities on the C2-acetamido group using the mutant uridylyltransferase AGX1F383A. The unnatural UDP-GlcNAc derivatives were examined as substrates for the human GlcNAc-transferase B3GNT2, where it was found that modified donors were tolerated for transfer, albeit to a lesser extent than the natural UDP-GlcNAc substrate. When the GlcNAc derivatives were examined as acceptor substrates for the human Gal-transferase B4GalT1, all derivatives were well tolerated and the enzyme could successfully form derivatized LacNAcs. B3GNT2 was also used to exo-enzymatically install GlcNAc and unnatural GlcNAc derivatives on cell-surface glycans. GlcNAc- or GlcNAz-engineered cells were further extended by B4GalT1 and UDP-Gal, producing LacNAc- or LacNAz-engineered cells. Our proof-of-concept glyco-engineering labeling strategy is amenable to different cell types and our work expands the exo-enzymatic glycan editing toolbox to selectively introduce unnatural type 2 LacNAc motifs.

Imidazolone as an Amide Bioisostere in the Development of β-1,3-N-Acetylglucosaminyltransferase 2 (B3GNT2) Inhibitors

B3GNT2 is responsible for elongation of cell surface long-chain polylactosamine, which influences the regulation of the immune response, making it an attractive target for immunomodulation. In the development of amide containing B3GNT2 inhibitors guided by structure-based drug design, imidazolones were found to successfully serve as amide bioisosteres. This novel imidazolone isosteric strategy alleviated torsional strain of the amide bond on binding to B3GNT2 and improved potency, isoform selectivity, as well as certain physicochemical and pharmacokinetic properties. Herein, we present the synthesis, SAR, X-ray cocrystal structures, and in vivo PK properties of imidazol-4-ones in the context of B3GNT2 inhibition.

Identification of a carbohydrate recognition motif of purinergic receptors

As a major class of biomolecules, carbohydrates play indispensable roles in various biological processes. However, it remains largely unknown how carbohydrates directly modulate important drug targets, such as G-protein coupled receptors (GPCRs). Here, we employed P2Y purinoceptor 14 (P2Y14), a drug target for inflammation and immune responses, to uncover the sugar nucleotide activation of GPCRs. Integrating molecular dynamics simulation with functional study, we identified the uridine diphosphate (UDP)-sugar-binding site on P2Y14, and revealed that a UDP-glucose might activate the receptor by bridging the transmembrane (TM) helices 2 and 7. Between TM2 and TM7 of P2Y14, a conserved salt bridging chain (K2.60-D2.64-K7.35-E7.36 [KDKE]) was identified to distinguish different UDP-sugars, including UDP-glucose, UDP-galactose, UDP-glucuronic acid, and UDP-N-acetylglucosamine. We identified the KDKE chain as a conserved functional motif of sugar binding for both P2Y14 and P2Y purinoceptor 12 (P2Y12), and then designed three sugar nucleotides as agonists of P2Y12. These results not only expand our understanding for activation of purinergic receptors but also provide insights for the carbohydrate drug development for GPCRs.

A Scan of Pleiotropic Immune Mediated Disease Genes Identifies Novel Determinants of Baseline FVIII Inhibitor Status in Hemophilia-A

Hemophilia-A (HA) is caused by heterogeneous loss-of-function factor (F)VIII gene (F8)-mutations and deficiencies in plasma-FVIII-activity that impair intrinsic-pathway-mediated coagulation-amplification. The standard-of-care for severe-HA-patients is regular infusions of therapeutic-FVIII-proteins (tFVIIIs) but ~30% develop neutralizing-tFVIII-antibodies called "FVIII-inhibitors (FEIs)" and become refractory. We used the PATH study and ImmunoChip to scan immune-mediated-disease (IMD)-genes for novel and/or replicated genomic-sequence-variations associated with baseline-FEI-status while accounting for non-independence of data due to genetic-relatedness and F8-mutational-heterogeneity. The baseline-FEI-status of 450 North American PATH subjects-206 with black-African-ancestry and 244 with white-European-ancestry-was the dependent variable. The F8-mutation-data and a genetic-relatedness matrix were incorporated into a binary linear-mixed model of genetic association with baseline-FEI-status. We adopted a gene-centric-association-strategy to scan, as candidates, pleiotropic-IMD-genes implicated in the development of either ³2 autoimmune-/autoinflammatory-disorders (AADs) or ³1 AAD and FEIs. Baseline-FEI-status was significantly associated with SNPs assigned to NOS2A (rs117382854; p=3.2E-6) and B3GNT2 (rs10176009; p=5.1E-6), which have functions in anti-microbial-/-tumoral-immunity. Among IMD-genes implicated in FEI-risk previously, we identified strong associations with CTLA4 assigned SNPs (p=2.2E-5). The F8-mutation-effect underlies ~15% of the total heritability for baseline-FEI-status. Additive genetic heritability and SNPs in IMD-genes account for >50% of the patient-specific variability in baseline-FEI-status. Race is a significant determinant independent of F8-mutation-effects and non-F8-genetics.

Molecular mechanism of decision-making in glycosaminoglycan biosynthesis

Two major glycosaminoglycan types, heparan sulfate (HS) and chondroitin sulfate (CS), control many aspects of development and physiology in a type-specific manner. HS and CS are attached to core proteins via a common linker tetrasaccharide, but differ in their polymer backbones. How core proteins are specifically modified with HS or CS has been an enduring mystery. By reconstituting glycosaminoglycan biosynthesis in vitro, we establish that the CS-initiating N-acetylgalactosaminyltransferase CSGALNACT2 modifies all glycopeptide substrates equally, whereas the HS-initiating N-acetylglucosaminyltransferase EXTL3 is selective. Structure-function analysis reveals that acidic residues in the glycopeptide substrate and a basic exosite in EXTL3 are critical for specifying HS biosynthesis. Linker phosphorylation by the xylose kinase FAM20B accelerates linker synthesis and initiation of both HS and CS, but has no effect on the subsequent polymerisation of the backbone. Our results demonstrate that modification with CS occurs by default and must be overridden by EXTL3 to produce HS.

Proteomic cardiovascular risk assessment in chronic kidney disease

AIMS

Chronic kidney disease (CKD) is widely prevalent and independently increases cardiovascular risk. Cardiovascular risk prediction tools derived in the general population perform poorly in CKD. Through large-scale proteomics discovery, this study aimed to create more accurate cardiovascular risk models.

METHODS AND RESULTS

Elastic net regression was used to derive a proteomic risk model for incident cardiovascular risk in 2182 participants from the Chronic Renal Insufficiency Cohort. The model was then validated in 485 participants from the Atherosclerosis Risk in Communities cohort. All participants had CKD and no history of cardiovascular disease at study baseline when ∼5000 proteins were measured. The proteomic risk model, which consisted of 32 proteins, was superior to both the 2013 ACC/AHA Pooled Cohort Equation and a modified Pooled Cohort Equation that included estimated glomerular filtrate rate. The Chronic Renal Insufficiency Cohort internal validation set demonstrated annualized receiver operating characteristic area under the curve values from 1 to 10 years ranging between 0.84 and 0.89 for the protein and 0.70 and 0.73 for the clinical models. Similar findings were observed in the Atherosclerosis Risk in Communities validation cohort. For nearly half of the individual proteins independently associated with cardiovascular risk, Mendelian randomization suggested a causal link to cardiovascular events or risk factors. Pathway analyses revealed enrichment of proteins involved in immunologic function, vascular and neuronal development, and hepatic fibrosis.

CONCLUSION

In two sizeable populations with CKD, a proteomic risk model for incident cardiovascular disease surpassed clinical risk models recommended in clinical practice, even after including estimated glomerular filtration rate. New biological insights may prioritize the development of therapeutic strategies for cardiovascular risk reduction in the CKD population.

A BRAF mutation-associated gene risk model for predicting the prognosis of melanoma

BRAF mutation plays an important role in the pathogenesis and progression of melanoma and is correlated to the prognosis of melanoma patients. However, fewer studies have attempted to develop a BRAF mutation-associated gene risk model for predicting the prognosis of melanoma. The current research explores BRAF mutation-related biological features in melanoma and establishes a prognostic signature. First, we identified three significantly enriched KEGG pathways (glycosphingolipid biosynthesis - ganglio series, ether lipid metabolism, and glycosaminoglycan biosynthesis - keratan sulfate) and corresponding genes in the BRAF mutant group by gene set enrichment analysis. We then developed a prognostic signature based on 7 BRAF-associated genes (PLA2G2D, FUT8, PLA2G4E, PLA2G5, PLA2G1B, B3GNT2, and ST3GAL5) and assessed its prediction accuracy using ROC curve analysis. Finally, the nomogram was established according to the prognostic signature and independent clinical characteristics to predict the survival of melanoma patients. Furthermore, we found higher proportions of naive B cells, plasma cells, CD8 T cells, CD4 memory-activated T cells, and regulatory T cells in the low-risk group. Whereas lower proportions of M0, M1, and M2 macrophages and resting NK cells were observed in the high-risk group. The analysis also showed a significantly higher expression of immune checkpoint molecules (PD-1, PD-L1, CTLA4, BTLA, CD28, CD80, CD86, HAVCR2, ICOS, LAG3, and TIGIT) in the low-risk group. Our results provide novel insights into the effect of BRAF mutation on melanoma growth and indicate a promising direction toward immunotherapy and precision medicine in melanoma patients.

Diverse mechanisms of polysaccharide biosynthesis, assembly and secretion across kingdoms

Polysaccharides are essential biopolymers produced in all kingdoms of life. On the cell surface, they represent versatile architectural components, forming protective capsules and coats, cell walls, or adhesives. Extracellular polysaccharide (EPS) biosynthesis mechanisms differ based on the cellular localization of polymer assembly. Some polysaccharides are first synthesized in the cytosol and then extruded by ATP powered transporters [1]. In other cases, the polymers are assembled outside the cell [2], synthesized and secreted in a single step [3], or deposited on the cell surface via vesicular trafficking [4]. This review focuses on recent insights into the biosynthesis, secretion, and assembly of EPS in microbes, plants and vertebrates. We focus on comparing the sites of biosynthesis, secretion mechanisms, and higher-order EPS assemblies.

N-Glycosylation of LRP6 by B3GnT2 Promotes Wnt/β-Catenin Signalling

Reception of Wnt signals by cells is predominantly mediated by Frizzled receptors in conjunction with a co-receptor, the latter being LRP6 or LRP5 for the Wnt/β-catenin signalling pathway. It is important that cells maintain precise control of receptor activation events in order to properly regulate Wnt/β-catenin signalling as aberrant signalling can result in disease in humans. Phosphorylation of the intracellular domain (ICD) of LRP6 is well known to regulate Wntβ-catenin signalling; however, less is known for regulatory post-translational modification events within the extracellular domain (ECD). Using a cell culture-based expression screen for functional regulators of LRP6, we identified a glycosyltransferase, B3GnT2-like, from a teleost fish (medaka) cDNA library, that modifies LRP6 and regulates Wnt/β-catenin signalling. We provide both gain-of-function and loss-of-function evidence that the single human homolog, B3GnT2, promotes extension of polylactosamine chains at multiple N-glycans on LRP6, thereby enhancing trafficking of LRP6 to the plasma membrane and promoting Wnt/β-catenin signalling. Our findings further highlight the importance of LRP6 as a regulatory hub in Wnt signalling and provide one of the few examples of how a specific glycosyltransferase appears to selectively target a signalling pathway component to alter cellular signalling events.

Decoding Strategies to Evade Immunoregulators Galectin-1, -3, and -9 and Their Ligands as Novel Therapeutics in Cancer Immunotherapy

Galectins are a family of ß-galactoside-binding proteins that play a variety of roles in normal physiology. In cancer, their expression levels are typically elevated and often associated with poor prognosis. They are known to fuel a variety of cancer progression pathways through their glycan-binding interactions with cancer, stromal, and immune cell surfaces. Of the 15 galectins in mammals, galectin (Gal)-1, -3, and -9 are particularly notable for their critical roles in tumor immune escape. While these galectins play integral roles in promoting cancer progression, they are also instrumental in regulating the survival, differentiation, and function of anti-tumor T cells that compromise anti-tumor immunity and weaken novel immunotherapies. To this end, there has been a surge in the development of new strategies to inhibit their pro-malignancy characteristics, particularly in reversing tumor immunosuppression through galectin-glycan ligand-targeting methods. This review examines some new approaches to evading Gal-1, -3, and -9-ligand interactions to interfere with their tumor-promoting and immunoregulating activities. Whether using neutralizing antibodies, synthetic peptides, glyco-metabolic modifiers, competitive inhibitors, vaccines, gene editing, exo-glycan modification, or chimeric antigen receptor (CAR)-T cells, these methods offer new hope of synergizing their inhibitory effects with current immunotherapeutic methods and yielding highly effective, durable responses.

Structural basis for the synthesis of the core 1 structure by C1GalT1

C1GalT1 is an essential inverting glycosyltransferase responsible for synthesizing the core 1 structure, a common precursor for mucin-type O-glycans found in many glycoproteins. To date, the structure of C1GalT1 and the details of substrate recognition and catalysis remain unknown. Through biophysical and cellular studies, including X-ray crystallography of C1GalT1 complexed to a glycopeptide, we report that C1GalT1 is an obligate GT-A fold dimer that follows a S_N2 mechanism. The binding of the glycopeptides to the enzyme is mainly driven by the GalNAc moiety while the peptide sequence provides optimal kinetic and binding parameters. Interestingly, to achieve glycosylation, C1GalT1 recognizes a high-energy conformation of the α-GalNAc-Thr linkage, negligibly populated in solution. By imposing this 3D-arrangement on that fragment, characteristic of α-GalNAc-Ser peptides, C1GalT1 ensures broad glycosylation of both acceptor substrates. These findings illustrate a structural and mechanistic blueprint to explain glycosylation of multiple acceptor substrates, extending the repertoire of mechanisms adopted by glycosyltransferases.

The glycosyltransferase C1GalT1 directs a key step in protein O-glycosylation important for the expression of the cancer-associated Tn and T antigens. Here, the authors provide molecular insights into the function of C1GalT1 by solving the crystal structure of the Drosophila enzyme-substrate complex.

MOXD1 knockdown suppresses the proliferation and tumor growth of glioblastoma cells via ER stress-inducing apoptosis

Oxygenase-catalyzed reduction and activation of oxygen molecules and the incorporation of oxygen atoms into organic molecules are undoubtedly necessary in the process of tumor development, and it is also one of the research hotspots in recent years. MOXD1 belongs to the copper-dependent monooxygenase family. The expression of MOXD1 is one of the characteristics of early tumor development. However, it is not understandable that the biological function and molecular mechanism of MOXD1 in Glioblastoma (GBM). In this study, high MOXD1 expression is strongly associated with poor survival of the patient with GBM. Moreover. MOXD1 knockdown can inhibit cell viability, proliferation, migration, invasion, and tumorigenesis of GBM cells. This is also proven for the first time that MOXD1 can bind to β3GnT2 and affect the glycosylation modification of some proteins. In addition, knockdown of MOXD1 induces endoplasmic reticulum (ER) stress and triggers the ER–mitochondrial apoptosis pathway. Taken together, these results reveal that MOXD1 is involved in the occurrence and development of GBM, and also provide a new strategy for targeted therapy.

How to extend your (polylactosamine) antennae

The elongated antennae decorating eukaryotic glycans are built from polylactosamine repeats. Polylactosamine forms a lectin recognition site and also acts as a platform for presenting diverse additional modifications (e.g., terminal cell-surface antigens); it therefore plays important roles in cell adherence, development, and immunity. Two new papers present a detailed structural and mechanistic investigation of β1-3-N-acetylgucosaminyltransferase 2, a key enzyme in antennae synthesis. The resulting insights will also help decipher other members of GT31, the single largest human glycosyltransferase family.