Sugar-Binding Profiles of Chitin-Binding Lectins from the Hevein Family: A Comprehensive Study

Specificity of widely used lectins as probed with oligosaccharide and plant polysaccharide arrays

Glycan-binding specificity was studied for Jacalin, RCA 120, SBA, PHA-L, PHA-E, WGA, UEA, AAL, LTL, LEL, SNA, DSA, LCA, MAH and Con A, lectins widely used in histochemistry. Oligosaccharide- and polysaccharide-based glycan arrays were applied. Expected specificity was confirmed for only 6 of the 15 lectins and the glycan binding profiles of some lectins were dramatically broader than generally accepted. WGA, LEL and DSA known as chitooligosaccharide-specific, were unexpectedly polyreactive, binding to other glycans with the same affinity as to chitobiose, ABH antigens and oligolactosamines (unsubstituted and sialylated). SBA, in addition to expected binding to glycans with terminal GalNAcα, also had high affinity for the GM1 ganglioside. MAH demonstrated much higher affinity to a variety of sulfated glycans compared to Neu5Acα2-3Galβ1-3GalNAcα. Contrary to the common view, LCA demonstrated the maximum binding to (GlcNAcβ1-2Manα1)2-3,6-Manβ1-4GlcNAcβ1-4GlcNAc N-glycan, while it had no interaction with corresponding Gal or Neu5Ac terminated versions. This observed polyreactivity of some lectins casts doubt on their use in accurately determining the presence of a specific glycan structure by histochemical studies. However, comparisons of sera from healthy and diseased individuals with help of a lectin array can easily establish differences in glycosylation patterns and presumptive glycan identities, which can later be clarified using more accurate methods of structural analysis.

Investigating diversity and similarity between CBM13 modules and ricin-B lectin domains using sequence similarity networks

BACKGROUND

The CBM13 family comprises carbohydrate-binding modules that occur mainly in enzymes and in several ricin-B lectins. The ricin-B lectin domain resembles the CBM13 module to a large extent. Historically, ricin-B lectins and CBM13 proteins were considered completely distinct, despite their structural and functional similarities.

RESULTS

In this data mining study, we investigate structural and functional similarities of these intertwined protein groups. Because of the high structural and functional similarities, and differences in nomenclature usage in several databases, confusion can arise. First, we demonstrate how public protein databases use different nomenclature systems to describe CBM13 modules and putative ricin-B lectin domains. We suggest the introduction of a novel CBM13 domain identifier, as well as the extension of CAZy cross-references in UniProt to guard the distinction between CAZy and non-CAZy entries in public databases. Since similar problems may occur with other lectin families and CBM families, we suggest the introduction of novel CBM InterPro domain identifiers to all existing CBM families. Second, we investigated phylogenetic, nomenclatural and structural similarities between putative ricin-B lectin domains and CBM13 modules, making use of sequence similarity networks. We concluded that the ricin-B/CBM13 superfamily may be larger than initially thought and that several putative ricin-B lectin domains may display CAZyme functionalities, although biochemical proof remains to be delivered.

CONCLUSIONS

Ricin-B lectin domains and CBM13 modules are associated groups of proteins whose database semantics are currently biased towards ricin-B lectins. Revision of the CAZy cross-reference in UniProt and introduction of a dedicated CBM13 domain identifier in InterPro may resolve this issue. In addition, our analyses show that several proteins with putative ricin-B lectin domains show very strong structural similarity to CBM13 modules. Therefore ricin-B lectin domains and CBM13 modules could be considered distant members of a larger ricin-B/CBM13 superfamily.

Decoding the mechanism governing the structural stability of wheat germ agglutinin and its isolated domains: A combined calorimetric, NMR, and MD simulation study

Wheat germ agglutinin (WGA) demonstrates potential as an oral delivery agent owing to its selective binding to carbohydrates and its capacity to traverse biological membranes. In this study, we employed differential scanning calorimetry and molecular dynamics simulations to comprehensively characterize the thermal unfolding process of both the complete lectin and its four isolated domains. Furthermore, we present the nuclear magnetic resonance structures of three domains that were previously lacking experimental structures in their isolated forms. Our results provide a collective understanding of the energetic and structural factors governing the intricate unfolding mechanism of the complete agglutinin, shedding light on the specific role played by each domain in this process. The analysis revealed negligible interdomain cooperativity, highlighting instead significant coupling between dimer dissociation and the unfolding of the more labile domains. By comparing the dominant interactions, we rationalized the stability differences among the domains. Understanding the structural stability of WGA opens avenues for enhanced drug delivery strategies, underscoring its potential as a promising carrier throughout the gastrointestinal environment.

Synthesis and unexpected binding of monofluorinated N,N'-diacetylchitobiose and LacdiNAc to wheat germ agglutinin

Fluorination of carbohydrate ligands of lectins is a useful approach to examine their binding profile, improve their metabolic stability and lipophilicity, and convert them into 19F NMR-active probes. However, monofluorination of monovalent carbohydrate ligands often leads to a decreased or completely lost affinity. By chemical glycosylation, we synthesized the full series of methyl β-glycosides of N,N'-diacetylchitobiose (GlcNAcβ(1-4)GlcNAcβ1-OMe) and LacdiNAc (GalNAcβ(1-4)GlcNAcβ1-OMe) systematically monofluorinated at all hydroxyl positions. A competitive enzyme-linked lectin assay revealed that the fluorination at the 6'-position of chitobioside resulted in an unprecedented increase in affinity to wheat germ agglutinin (WGA) by one order of magnitude. For the first time, we have characterized the binding profile of a previously underexplored WGA ligand LacdiNAc. Surprisingly, 4'-fluoro-LacdiNAc bound WGA even stronger than unmodified LacdiNAc. These observations were interpreted using molecular dynamic calculations along with STD and transferred NOESY NMR techniques, which gave evidence for the strengthening of CH/π interactions after deoxyfluorination of the side chain of the non-reducing GlcNAc. These results highlight the potential of fluorinated glycomimetics as high-affinity ligands of lectins and 19F NMR-active probes.

Glycan-directed SARS-CoV-2 inhibition by leek extract and lectins with insights into the mode-of-action of Concanavalin A

Four years after its outbreak, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remains a global challenge for human health. At its surface, SARS-CoV-2 features numerous extensively glycosylated spike proteins. This glycan coat supports virion docking and entry into host cells and at the same time renders the virus less susceptible to neutralizing antibodies. Given the high genetic plasticity of SARS-CoV-2 and the rapid emergence of immune escape variants, targeting the glycan shield by carbohydrate-binding agents emerges as a promising strategy. However, the potential of carbohydrate-targeting reagents as viral inhibitors remains underexplored. Here, we tested seven plant-derived carbohydrate-binding proteins, called lectins, and one crude plant extract for their antiviral activity against SARS-CoV-2 in two types of human lung cells: A549 cells ectopically expressing the ACE2 receptor and Calu-3 cells. We identified three lectins and an Allium porrum (leek) extract inhibiting SARS-CoV-2 infection in both cell systems with selectivity indices (SI) ranging between >2 and >299. Amongst these, the lectin Concanavalin A (Con A) exerted the most potent and broad activity against a panel of SARS-CoV-2 variants. We used multiplex super-resolution microscopy to address lectin interactions with SARS-CoV-2 and its host cells. Notably, we discovered that Con A not only binds to SARS-CoV-2 virions and their host cells, but also causes SARS-CoV-2 aggregation. Thus, Con A exerts a dual mode-of-action comprising both, antiviral and virucidal, mechanisms. These results establish Con A and other plant lectins as candidates for COVID-19 prevention and basis for further drug development.

LeGenD: determining N-glycoprofiles using an explainable AI-leveraged model with lectin profiling

Glycosylation affects many vital functions of organisms. Therefore, its surveillance is critical from basic science to biotechnology, including biopharmaceutical development and clinical diagnostics. However, conventional glycan structure analysis faces challenges with throughput and cost. Lectins offer an alternative approach for analyzing glycans, but they only provide glycan epitopes and not full glycan structure information. To overcome these limitations, we developed LeGenD, a lectin and AI-based approach to predict N-glycan structures and determine their relative abundance in purified proteins based on lectin-binding patterns. We trained the LeGenD model using 309 glycoprofiles from 10 recombinant proteins, produced in 30 glycoengineered CHO cell lines. Our approach accurately reconstructed experimentally-measured N-glycoprofiles of bovine Fetuin B and IgG from human sera. Explanatory AI analysis with SHapley Additive exPlanations (SHAP) helped identify the critical lectins for glycoprofile predictions. Our LeGenD approach thus presents an alternative approach for N-glycan analysis.

Spectroscopic and thermodynamic characterization of the interaction between sugar-stabilised silver nanoparticles and wheat germ agglutinin (WGA), a chitin binding lectin

Nanomaterials have lately been investigated in agriculture as eco-friendly and effective antifungal agents. Many nanomaterials, notably metal nanoparticles, have strong antifungal properties. Among metal nanoparticles, Ag nanoparticles have received the most attention as antifungal agents. Many plant lectins have been identified as antifungal agents. Conjugating AgNPs with antifungal lectins is thus expected to improve Ag nanoparticle antifungal efficacy. Understanding the molecular interactions and physical features of lectin-sugar-stabilised nanoparticle conjugates is critical for future applications. WGA has traditionally been used as an anti-tumor and antifungal agent. To investigate the prospect of developing an effective biocompatible antifungal system with applications in medicine and agriculture, fluorescence spectroscopy was used to investigate the interaction between sugar-stabilised silver nanoparticles and WGA. During the association, protein intrinsic fluorescence emission is suppressed by about ∼15 % at saturation, with no significant shift in fluorescence emission maxima. Binding tests reveal a strong bond. Stern-Volmer analysis of the quenching data indicates that the interaction happens via a static quenching process that induces complex formation. The study of hemagglutination activity and interaction experiments in the presence of particular sugar shows that the lectin's sugar-binding site is separate from the nanoparticle-binding site, and cell recognition is conserved in the lectin-nanoparticle complex. The Van't Hoff plot thermodynamic parameters suggest that the contact is hydrophobic. The fact that ΔGo is negative shows that the binding is a spontaneous process. CD spectroscopy experiments reveal that the lectin's secondary structure is not affected while binding to the nanoparticle. Our findings suggest that a stable WGA-silver nanoparticle combination may emerge for a variety of applications.

Genome-Wide Mining of Selaginella moellendorffii for Hevein-like Lectins and Their Potential Molecular Mimicry with SARS-CoV-2 Spike Glycoprotein

Multidisciplinary research efforts on potential COVID-19 vaccine and therapeutic candidates have increased since the pandemic outbreak of SARS-CoV-2 in 2019. This search has become imperative due to the increasing emergences and limited widely available medicines. The presence of bioactive anti-SARS-CoV-2 molecules was examined from various plant sources. Among them is a group of proteins called lectins that can bind carbohydrate moieties. In this article, we present ten novel, chitin-specific Hevein-like lectins that were derived from Selaginella moellendorffii v1.0's genome. The capacity of these lectin homologs to bind with the spike protein of SARS-CoV-2 was examined. Using the HDOCK server, 3D-modeled Hevein-domains were docked to the spike protein's receptor binding domain (RBD). The Smo446851, Smo125663, and Smo99732 interacted with Asn343-located complex N-glycan and RBD residues, respectively, with binding free energies of -17.5, -13.0, and -26.5 Kcal/mol. The molecular dynamics simulation using Desmond and the normal-state analyses via torsional coordinate association for the Smo99732-RBD complex using iMODS is characterized by overall higher stability and minimum deformity than the other lectin complexes. The three lectins interacting with carbohydrates were docked against five individual mutations that frequently occur in major SARS-CoV-2 variants. These were in the spike protein's receptor-binding motif (RBM), while Smo125663 and Smo99732 only interacted with the spike glycoprotein in a protein-protein manner. The precursors for the Hevein-like homologs underwent additional characterization, and their expressional profile in different tissues was studied. These in silico findings offered potential lectin candidates targeting key N-glycan sites crucial to the virus's virulence and infection.

Inhibitory potency of the nettle lectin on neovascularization: a biomolecule for carbohydrate-mediated targeting of angiogenesis

BACKGROUND

Current angiogenesis inhibitors target cellular vascularization processes, including proliferation, migration, and tube formation. In this study, we investigated the impact of Urtica dioica agglutinin (UDA) on the cellular vascularization process.

METHODS AND RESULTS

Various concentrations of UDA were applied to normal (HUVEC, MCF-10 A, and HDF from humans, and L-929 from mice) and cancer (A431 and U87 from humans, and 4T1 from mice) cell lines at different times. The MTT, cell migration assay, differentiation of endothelial cells, expression of VEGF-A/VEGF-R2, and integrin α2 were evaluated. The MTT results demonstrated that UDA was non-toxic to normal cells while inhibiting the growth of neoplastic cells. The migratory capacity of HUVECs and U87 glioblastoma cells was inhibited by UDA in the wound repair model. This lectin inhibited HUVEC-induced vessel sprouting in the collagen-cytodex matrix. In addition, UDA treatment reduced VEGF-integrin cross-talk in HUVECs, confirming the anti-angiogenic activity of this molecule.

CONCLUSIONS

Based on our findings, UDA may have an effect on cancer cell proliferation and vascularization events while causing minimal toxicity to normal cells via binding glyco-conjugates containing GlcNAc/man oligomers like EGFR. This is a blue clue for the angiogenesis-related therapeutic importance of UDA.

Spatiotemporal changes of tissue glycans depending on localization in cardiac aging

Heart failure is caused by various factors, making the underlying pathogenic mechanisms difficult to identify. Since cardiovascular disease tends to worsen over time, early diagnosis is key for treatment. In addition, understanding the qualitative changes in the heart associated with aging, where information on the direct influences of aging on cardiovascular disease is limited, would also be useful for treatment and diagnosis. To fill these research gaps, the focus of our study was to detect the structural and functional molecular changes associated with the heart over time, with a focus on glycans, which reflect the type and state of cells.

METHODS

We investigated glycan localization in the cardiac tissue of normal mice and their alterations during aging, using evanescent-field fluorescence-assisted lectin microarray, a technique based on lectin-glycan interaction, and lectin staining.

RESULTS

The glycan profiles in the left ventricle showed differences between the luminal side (medial) and wall side (lateral) regions. The medial region was characterized by the presence of sialic acid residues. Moreover, age-related changes in glycan profiles were observed at a younger age in the medial region. The difference in the age-related decrease in the level of α-galactose stained with Griffonia simplicifolia lectin-IB4 in different regions of the left ventricle suggests spatiotemporal changes in the number of microvessels.

CONCLUSIONS

The glycan profile, which retains diverse glycan structures, is supported by many cell populations, and maintains cardiac function. With further research, glycan localization and changes have the potential to be developed as a marker of the signs of heart failure.

Transport of the Proinflammatory Chemokines C-C Motif Chemokine Ligand 2 (MCP-1) and C-C Motif Chemokine Ligand 5 (RANTES) across the Intact Mouse Blood-Brain Barrier Is Inhibited by Heparin and Eprodisate and Increased with Systemic Inflammation

One important function of the vascular blood-brain barrier (BBB) is to facilitate neuroimmune communication. The BBB fulfills this function, in part, through its ability to transport cytokines and chemokines. C-C motif chemokine receptor 2 (CCL2) (MCP-1) and C-C motif chemokine receptor 5 (CCL5) (RANTES) are proinflammatory chemokines that mediate neuroimmune responses to acute insults and aspects of brain injury and neurodegenerative diseases; however, a blood-to-brain transport system has not been evaluated for either chemokine in vivo. Therefore, we determined whether CCL2 and CCL5 in blood can cross the intact BBB and enter the brain. Using CD-1 mice, we found that ¹²⁵I-labeled CCL2 and CCL5 crossed the BBB and entered the brain parenchyma. We next aimed to identify the mechanisms of ¹²⁵I-CCL2 and ¹²⁵I-CCL5 transport in an in situ brain perfusion model. We found that both heparin and eprodisate inhibited brain uptake of ¹²⁵I-CCL2 and ¹²⁵I-CCL5 in situ, whereas antagonists of their receptors, CCR2 or CCR5, respectively, did not, suggesting that heparan sulfates at the endothelial surface mediate BBB transport. Finally, we showed that CCL2 and CCL5 transport across the BBB increased following a single injection of 0.3 mg/kg lipopolysaccharide. These data demonstrate that CCL2 and CCL5 in the brain can derive, in part, from the circulation, especially during systemic inflammation. Further, binding to the BBB-associated heparan sulfate is a mechanism by which both chemokines can cross the intact BBB, highlighting a novel therapeutic target for treating neuroinflammation. SIGNIFICANCE STATEMENT: Our work demonstrates that C-C motif chemokine ligand 2 (CCL2) and C-C motif chemokine ligand 5 (CCL5) can cross the intact blood-brain barrier and that transport is robustly increased during inflammation. These data suggest that circulating CCL2 and CCL5 can contribute to brain levels of each chemokine. We further show that the transport of both chemokines is inhibited by heparin and eprodisate, suggesting that CCL2/CCL5-heparan sulfate interactions could be therapeutically targeted to limit accumulation of these chemokines in the brain.

Supramolecular Binding with Lectins: A New Route for Non-Covalent Functionalization of Polysaccharide Matrices

The chemical functionalization of polysaccharides to obtain functional materials has been of great interest in the last decades. This traditional synthetic approach has drawbacks, such as changing the crystallinity of the material or altering its morphology or texture. These modifications are crucial when a biogenic matrix is exploited for its hierarchical structure. In this work, the use of lectins and carbohydrate-binding proteins as supramolecular linkers for polysaccharide functionalization is proposed. As proof of concept, a deproteinized squid pen, a hierarchically-organized β-chitin matrix, was functionalized using a dye (FITC) labeled lectin; the lectin used was the wheat germ agglutinin (WGA). It has been observed that the binding of this functionalized protein homogenously introduces a new property (fluorescence) into the β-chitin matrix without altering its crystallographic and hierarchical structure. The supramolecular functionalization of polysaccharides with protein/lectin molecules opens up new routes for the chemical modification of polysaccharides. This novel approach can be of interest in various scientific fields, overcoming the synthetic limits that have hitherto hindered the technological exploitation of polysaccharides-based materials.

Effects of Urtica dioica agglutinin on glycotargeting of the vasculature: an in ovo study on chicken embryo

The angiogenesis process is a pivotal cellular process involved in both developmental and pathological circumstances. In this study we investigated effect of Urtica dioica agglutinin (UDA), as an unusual phyto-lectin from the chitin-binding protein family, on the angiogenesis of chicken embryos. The UDA was extracted from plant rhizomes and purified by affinity chromatography column. The activity of this lectin was assayed by hemagglutination test on the human RBCs. Anti-angiogenic effect of UDA on the extra-embryonic layer of the chick egg was studied in the different concentrations. Our results showed that the minimum concentration of UDA for agglutination were 48.00 and 15.00 µg mL^-1 in macro- and microscopic studies, respectively. Because the number and length of the vessels were dramatically decreased at 100 µg kg^-1 of UDA, the lectin had an inhibitory effect on angiogenesis of the embryonic vasculature of the chick. We concluded that UDA might target the vascularization events through binding to GlcNAc-conjugates. More investigations are needed to clarify the angiogenesis-related therapeutic roles of this interesting biomolecule.

Carbohydrate-binding protein from stinging nettle as fusion inhibitor for SARS-CoV-2 variants of concern

Urtica dioica agglutinin (UDA) is a carbohydrate-binding small monomeric protein isolated from stinging nettle rhizomes. It inhibits replication of a broad range of viruses, including coronaviruses, in multiple cell types, with appealing selectivity. In this work, we investigated the potential of UDA as a broad-spectrum antiviral agent against SARS-CoV-2. UDA potently blocks transduction of pseudotyped SARS-CoV-2 in A549.ACE2⁺-TMPRSS2 cells, with IC₅₀ values ranging from 0.32 to 1.22 µM. Furthermore, UDA prevents viral replication of the early Wuhan-Hu-1 strain in Vero E6 cells (IC₅₀ = 225 nM), but also the replication of SARS-CoV-2 variants of concern, including Alpha, Beta and Gamma (IC₅₀ ranging from 115 to 171 nM). In addition, UDA exerts antiviral activity against the latest circulating Delta and Omicron variant in U87.ACE2⁺ cells (IC₅₀ values are 1.6 and 0.9 µM, respectively). Importantly, when tested in Air-Liquid Interface (ALI) primary lung epithelial cell cultures, UDA preserves antiviral activity against SARS-CoV-2 (20A.EU2 variant) in the nanomolar range. Surface plasmon resonance (SPR) studies demonstrated a concentration-dependent binding of UDA to the viral spike protein of SARS-CoV-2, suggesting interference of UDA with cell attachment or subsequent virus entry. Moreover, in additional mechanistic studies with cell-cell fusion assays, UDA inhibited SARS-CoV-2 spike protein-mediated membrane fusion. Finally, pseudotyped SARS-CoV-2 mutants with N-glycosylation deletions in the S2 subunit of the spike protein remained sensitive to the antiviral activity of UDA. In conclusion, our data establish UDA as a potent fusion inhibitor for the current variants of SARS-CoV-2.

The architecture and operating mechanism of a cnidarian stinging organelle

The stinging organelles of jellyfish, sea anemones, and other cnidarians, known as nematocysts, are remarkable cellular weapons used for both predation and defense. Nematocysts consist of a pressurized capsule containing a coiled harpoon-like thread. These structures are in turn built within specialized cells known as nematocytes. When triggered, the capsule explosively discharges, ejecting the coiled thread which punctures the target and rapidly elongates by turning inside out in a process called eversion. Due to the structural complexity of the thread and the extreme speed of discharge, the precise mechanics of nematocyst firing have remained elusive⁷. Here, using a combination of live and super-resolution imaging, 3D electron microscopy, and genetic perturbations, we define the step-by-step sequence of nematocyst operation in the model sea anemone Nematostella vectensis. This analysis reveals the complex biomechanical transformations underpinning the operating mechanism of nematocysts, one of nature’s most exquisite biological micro-machines. Further, this study will provide insight into the form and function of related cnidarian organelles and serve as a template for the design of bioinspired microdevices.

The venomous stinging cells of jellyfish, anemones, and corals contain an organelle, the nematocyst, which explosively discharges a venom-laden thread. Here, the authors describe the nematocyst thread and its sub-structures in the sea anemone N. vectensis, revealing a complexity and sophistication underpinning this cellular weapon.

Lectins and lectibodies: potential promising antiviral agents

In nature, lectins are widely dispersed proteins that selectively recognize and bind to carbohydrates and glycoconjugates via reversible bonds at specific binding sites. Many viral diseases have been treated with lectins due to their wide range of structures, specificity for carbohydrates, and ability to bind carbohydrates. Through hemagglutination assays, these proteins can be detected interacting with various carbohydrates on the surface of cells and viral envelopes. This review discusses the most robust lectins and their rationally engineered versions, such as lectibodies, as antiviral proteins. Fusion of lectin and antibody’s crystallizable fragment (Fc) of immunoglobulin G (IgG) produces a molecule called a “lectibody” that can act as a carbohydrate-targeting antibody. Lectibodies can not only bind to the surface glycoproteins via their lectins and neutralize and clear viruses or infected cells by viruses but also perform Fc-mediated antibody effector functions. These functions include complement-dependent cytotoxicity (CDC), antibody-dependent cell-mediated cytotoxicity (ADCC), and antibody-dependent cell-mediated phagocytosis (ADCP). In addition to entering host cells, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein S1 binds to angiotensin-converting enzyme 2 (ACE2) and downregulates it and type I interferons in a way that may lead to lung disease. The SARS-CoV-2 spike protein S1 and human immunodeficiency virus (HIV) envelope are heavily glycosylated, which could make them a major target for developing vaccines, diagnostic tests, and therapeutic drugs. Lectibodies can lead to neutralization and clearance of viruses and cells infected by viruses by binding to glycans located on the envelope surface (e.g., the heavily glycosylated SARS-CoV-2 spike protein).

Identification of distinct N-glycosylation patterns on extracellular vesicles from small-cell and non-small-cell lung cancer cells

Asparagine-linked glycosylation (N-glycosylation) of proteins in the cancer secretome has been gaining increasing attention as a potential biomarker for cancer detection and diagnosis. Small extracellular vesicles (sEVs) constitute a large part of the cancer secretome, yet little is known about whether their N-glycosylation status reflects known cancer characteristics. Here, we investigated the N-glycosylation of sEVs released from small-cell lung carcinoma (SCLC) and non-small-cell lung carcinoma (NSCLC) cells. We found that the N-glycans of SCLC-sEVs were characterized by the presence of structural units also found in the brain N-glycome, while NSCLC-sEVs were dominated by typical lung-type N-glycans with NSCLC-associated core fucosylation. In addition, lectin-assisted N-glycoproteomics of SCLC-sEVs and NSCLC-sEVs revealed that integrin αV was commonly expressed in sEVs of both cancer cell types, while the epithelium-specific integrin α6β4 heterodimer was selectively expressed in NSCLC-sEVs. Importantly, N-glycomics of the immuno-purified integrin α6 from NSCLC-sEVs identified NSCLC-type N-glycans on this integrin subunit. Thus, we conclude that protein N-glycosylation in lung cancer sEVs may potentially reflect the histology of lung cancers.

Interleukin-22 regulates B3GNT7 expression to induce fucosylation of glycoproteins in intestinal epithelial cells

Interleukin (IL)-22 is a cytokine that plays a critical role in intestinal epithelial homeostasis. Its downstream functions are mediated through interaction with the heterodimeric IL-22 receptor and subsequent activation of signal transducer and activator of transcription 3 (STAT3). IL-22 signaling can induce transcription of genes necessary for intestinal epithelial cell proliferation, tissue regeneration, tight junction fortification, and antimicrobial production. Recent studies have also implicated IL-22 signaling in the regulation of intestinal epithelial fucosylation in mice. However, whether IL-22 regulates intestinal fucosylation in human intestinal epithelial cells and the molecular mechanisms that govern this process are unknown. Here, in experiments performed in human cell lines and human-derived enteroids, we show that IL-22 signaling regulates expression of the B3GNT7 transcript, which encodes a β1-3-N-acetylglucosaminyltransferase that can participate in the synthesis of poly-N-acetyllactosamine (polyLacNAc) chains. Additionally, we find that IL-22 signaling regulates levels of the α1-3-fucosylated Lewis X (Lex) blood group antigen, and that this glycan epitope is primarily displayed on O-glycosylated intestinal epithelial glycoproteins. Moreover, we show that increased expression of B3GNT7 alone is sufficient to promote increased display of Lex-decorated carbohydrate glycan structures primarily on O-glycosylated intestinal epithelial glycoproteins. Together, these data identify B3GNT7 as an intermediary in IL-22-dependent induction of fucosylation of glycoproteins and uncover a novel role for B3GNT7 in intestinal glycosylation.

Evaluation of Glycan-Binding Specificity by Glycoconjugate Microarray with an Evanescent-Field Fluorescence Detection System

Glycan microarray is an essential tool to study glycan-binding proteins called lectins. Using glycan microarrays, glycan-binding specificity can be analyzed by incubation with an array in which a series of glycans are immobilized. Various research groups in the world have developed glycan microarray. Among them, our glycan microarray has two unique points: one is the incorporation of the evanescent-field fluorescence detection system, and another is the use of multivalent glycopolymers. These two unique properties allow high-sensitive detection from a relatively limited amount of only nanograms of lectins, which could even be applied in crude samples such as cell lysates and cell culture media. Thus, this system is suitable for the first screening of lectins, lectin-like molecules, lectin candidates, and lectin mutants. Here we describe the protocols to analyze glycan-binding specificity of lectins using our glycan microarray system.

CH-π Interactions in Glycan Recognition

Carbohydrate recognition is crucial for biological processes ranging from development to immune system function to host-pathogen interactions. The proteins that bind glycans are faced with a daunting task: to coax these hydrophilic species out of water and into a binding site. Here, we examine the forces underlying glycan recognition by proteins. Our previous bioinformatic study of glycan-binding sites indicated that the most overrepresented side chains are electron-rich aromatic residues, including tyrosine and tryptophan. These findings point to the importance of CH-π interactions for glycan binding. Studies of CH-π interactions show a strong dependence on the presence of an electron-rich π system, and the data indicate binding is enhanced by complementary electronic interactions between the electron-rich aromatic ring and the partial positive charge of the carbohydrate C-H protons. This electronic dependence means that carbohydrate residues with multiple aligned highly polarized C-H bonds, such as β-galactose, form strong CH-π interactions, whereas less polarized residues such as α-mannose do not. This information can guide the design of proteins to recognize sugars and the generation of ligands for proteins, small molecules, or catalysts that bind sugars.

Recombinant protein linker production as a basis for non-invasive determination of single-cell yeast age in heterogeneous yeast populations

The physiological and metabolic diversity of a yeast culture is the sum of individual cell phenotypes. As well as environmental conditions, genetics, and numbers of cell divisions, a major factor influencing cell characteristics is cell age. A postcytokinesis bud scar on the mother cell, a benchmark in the replicative life span, is a quantifiable indicator of cell age, characterized by significant amounts of chitin. We developed a binding process for visualizing the bud scars of Saccharomyces pastorianus var. carlsbergensis using a protein linker containing a polyhistidine tag, a superfolder green fluorescent protein (sfGFP), and a chitin-binding domain (His6-SUMO-sfGFP-ChBD). The binding did not affect yeast viability; thus, our method provides the basis for non-invasive cell age determination using flow cytometry. The His6-SUMO-sfGFP-ChBD protein was synthesized in Escherichia coli, purified using two-stage chromatography, and checked for monodispersity and purity. Linker-cell binding and the characteristics of the bound complex were determined using flow cytometry and confocal laser scanning microscopy (CLSM). Flow cytometry showed that protein binding increased to 60 455 ± 2706 fluorescence units per cell. The specific coupling of the linker to yeast cells was additionally verified by CLSM and adsorption isotherms using yeast cells, E. coli cells, and chitin resin. We found a relationship between the median bud scar number, the median of the fluorescence units, and the chitin content of yeast cells. A fast measurement of yeast population dynamics by flow cytometry is possible, using this protein binding technique. Rapid qualitative determination of yeast cell age distribution can therefore be performed.

Chemoenzymatic modular assembly of O-GalNAc glycans for functional glycomics

O-GalNAc glycans (or mucin O-glycans) play pivotal roles in diverse biological and pathological processes, including tumor growth and progression. Structurally defined O-GalNAc glycans are essential for functional studies but synthetic challenges and their inherent structural diversity and complexity have limited access to these compounds. Herein, we report an efficient and robust chemoenzymatic modular assembly (CEMA) strategy to construct structurally diverse O-GalNAc glycans. The key to this strategy is the convergent assembly of O-GalNAc cores 1-4 and 6 from three chemical building blocks, followed by enzymatic diversification of the cores by 13 well-tailored enzyme modules. A total of 83 O-GalNAc glycans presenting various natural glycan epitopes are obtained and used to generate a unique synthetic mucin O-glycan microarray. Binding specificities of glycan-binding proteins (GBPs) including plant lectins and selected anti-glycan antibodies towards these O-GalNAc glycans are revealed by this microarray, promoting their applicability in functional O-glycomics. Serum samples from colorectal cancer patients and healthy controls are assayed using the array reveal higher bindings towards less common cores 3, 4, and 6 than abundant cores 1 and 2, providing insights into O-GalNAc glycan structure-activity relationships.

Predictive modeling of complex ABO glycan phenotypes by lectin microarrays

Serological classification of individuals as A, B, O, or AB is a mainstay of blood banking. ABO blood groups or ABH antigens, in addition to other surface glycans, act as unique red blood cell (RBC) signatures and direct immune responses. ABO subgroups present as weakened, mixed field, or unexpected reactivity with serological reagents, but specific designations remain complex. Lectins detect glycan motifs with some recognizing ABH antigens. We evaluated a 45-probe lectin microarray to rapidly analyze ABO blood groups and associated unique glycan signatures within complex biological samples on RBC surface glycoproteins. RBC membrane glycoproteins were prepared from donor RBCs, n = 20 for each blood group. ABO blood group was distinguishable by lectin array, including variations in ABH antigen expression not observed with serology. Principal component analysis highlighted broad ABO blood group clusters with unexpected high and low antigen expression and variations were confirmed with ABH antibody immunoblotting. Using a subset of lectins provided an accurate method to predict an ABO serological phenotype. Lectin microarray highlighted the importance of ABO localization on glycoproteins and glycolipids and pointed to increased glycocalyx complexity associated with the expression of A and B antigens including high mannose and branched polylactosamine. Thus, lectins identified subtle surface ABO blood group glycoprotein density variations not detected by routine serological methods. Transfusion services observe alterations in ABH expression during malignancy, and ABO incompatible solid organ transplantation is not without risk of rejection. The presented methods may identify subtle but clinically significant ABO blood group differences for transfusion and transplantation.

In Vitro Characterization of the Carbohydrate-Binding Agents HHA, GNA, and UDA as Inhibitors of Influenza A and B Virus Replication

Here, we report on the anti-influenza virus activity of the mannose-binding agents Hippeastrum hybrid agglutinin (HHA) and Galanthus nivalis agglutinin (GNA) and the (N-acetylglucosamine) _n -specific Urtica dioica agglutinin (UDA). These carbohydrate-binding agents (CBA) strongly inhibited various influenza A(H1N1), A(H3N2), and B viruses in vitro, with 50% effective concentration values ranging from 0.016 to 83 nM, generating selectivity indexes up to 125,000. Somewhat less activity was observed against A/Puerto Rico/8/34 and an A(H1N1)pdm09 strain. In time-of-addition experiments, these CBA lost their inhibitory activity when added 30 min postinfection (p.i.). Interference with virus entry processes was also evident from strong inhibition of virus-induced hemolysis at low pH. However, a direct effect on acid-induced refolding of the viral hemagglutinin (HA) was excluded by the tryptic digestion assay. Instead, HHA treatment of HA-expressing cells led to a significant reduction of plasma membrane mobility. Crosslinking of membrane glycoproteins, through interaction with HA, could also explain the inhibitory effect on the release of newly formed virions when HHA was added at 6 h p.i. These CBA presumably interact with one or more N-glycans on the globular head of HA, since their absence led to reduced activity against mutant influenza B viruses and HHA-resistant A(H1N1) viruses. The latter condition emerged only after 33 cell culture passages in the continuous presence of HHA, and the A(H3N2) virus retained full sensitivity even after 50 passages. Thus, these CBA qualify as potent inhibitors of influenza A and B viruses in vitro with a pleiotropic mechanism of action and a high barrier for viral resistance.

C-Terminally tagged NA in replication-competent influenza A viruses reveals differences in glycan profiles between NA and HA

Glycans attached to the viruses regulate their pathogenicity, immunogenicity, and antigenicity. We have previously shown that lectin microarray provided an easy and highly sensitive platform for analyzing glycan profiles of hemagglutinin (HA) of influenza A viruses in culture supernatants. On the other hand, the system is not applicable for neuraminidase (NA), the other viral glycoprotein of influenza A viruses, due to the limited availability of specific antibodies used to detect NA in the lectin microarray. Accordingly, we established replication-competent viruses harboring the short peptide-tag sequence at the C-terminus of NA in this study. The generated viruses underwent normal proliferation cycles and showed similar properties to the wild-type viruses. Lectin microarray analyses of the tagged NA enriched from the viral particles showed that glycan profiles of NA were mostly occupied by mannose-type glycans. Interestingly, the profiles were distinct from those of HA separated from the same particle preparation, in which core-fucosylated complex-type N-glycans terminating with non-sialylated N-acetyllactosamine were dominant. Collectively, this study provides novel platforms for the analyses of the distinction between the glycan profiles of NA and HA, and contributes to a better understanding of later stages of the viral life cycles through analyzing the glycans attached to NA.

Determination of the glycoprotein specificity of lectins on cell membranes through oxidative proteomics

The cell membrane is composed of a network of glycoconjugates including glycoproteins and glycolipids that presents a dense matrix of carbohydrates playing critical roles in many biological processes. Lectin-based technology has been widely used to characterize glycoconjugates in tissues and cell lines. However, their specificity toward their putative glycan ligand and sensitivity in situ have been technologically difficult to study. Additionally, because they recognize primarily glycans, the underlying glycoprotein targets are generally not known. In this study, we employed lectin proximity oxidative labeling (Lectin PROXL) to identify cell surface glycoproteins that contain glycans that are recognized by lectins. Commonly used lectins were modified with a probe to produce hydroxide radicals in the proximity of the labeled lectins. The underlying polypeptides of the glycoproteins recognized by the lectins are oxidized and identified by the standard proteomic workflow. As a result, approximately 70% of identified glycoproteins were oxidized in situ by all the lectin probes, while only 5% of the total proteins were oxidized. The correlation between the glycosites and oxidation sites demonstrated the effectiveness of the lectin probes. The specificity and sensitivity of each lectin were determined using site-specific glycan information obtained through glycomic and glycoproteomic analyses. Notably, the sialic acid-binding lectins and the fucose-binding lectins had higher specificity and sensitivity compared to other lectins, while those that were specific to high mannose glycans have poor sensitivity and specificity. This method offers an unprecedented view of the interactions of lectins with specific glycoproteins as well as protein networks that are mediated by specific glycan types on cell membranes.

Purification of natural neutral N-glycans by using two-dimensional hydrophilic interaction liquid chromatography × porous graphitized carbon chromatography for glycan-microarray assay

Glycan microarray for studying carbohydrate-protein interactions requires diverse classes of well-defined glycan standards. In this study, a purification strategy was established based on two-dimensional hydrophilic interaction liquid chromatography and porous graphitized carbon chromatography (HILIC × PGC) for the acquisition of neutral N-glycan standards from natural source. A total of thirty-one N-glycan compounds including seven pairs of isomers with the amounts from 0.7 to 230.0 nmol were isolated from ovalbumin as the model glycoconjugate. The purified N-glycans covered high-mannose, hybrid as well as multi-antenna asymmetric complex types. The purity of majority of these N-glycans was higher than 90%. Detailed structures of the N-glycan compounds were verified via negative ion tandem MS analysis, in which specific diagnostic ions including D- and E-ions were used to identify isomeric and terminal fine structures. The tag-free glycan compounds with well-defined structures, purity and amounts were finally assembled on the glass slide through neoglycolipid technology. Microarray binding assay of purified glycans with WGA lectin indicated the potential of the established strategy in glycan library expansion and functional glycomics.

Succinylated Wheat Germ Agglutinin Colocalizes with the Toxoplasma gondii Cyst Wall Glycoprotein CST1

The glycosylated mucin domain of the Toxoplasma gondii cyst wall glycoprotein CST1 is heavily stained by Dolichos biflorus agglutinin, a lectin that binds to N-acetylgalactosamine. The cyst wall is also heavily stained by the chitin binding lectin succinylated wheat germ agglutinin (s-WGA), which selectively binds to N-acetylglucosamine-decorated structures. Here, we tracked the localization of N-acetylglucosamine-decorated structures that bind to s-WGA in immature and mature in vitro cysts. s-WGA localization was observed at the cyst periphery 6 h after the differentiation of the tachyzoite-stage parasitophorous vacuole. By day 1 and at all later times after differentiation, s-WGA was localized in a continuous staining pattern at the cyst wall. Coinciding with the maturation of the cyst matrix by day 3 of cyst development, s-WGA also localized in a continuous matrix pattern inside the cyst. s-WGA localized in both the outer and inner layer regions of the cyst wall and in a continuous matrix pattern inside mature 7- and 10-day-old cysts. In addition, s-WGA colocalized in the cyst wall with CST1, suggesting that N-acetylglucosamine- and N-acetylgalactosamine-decorated molecules colocalized in the cyst wall. In contrast to CST1, GRA4, and GRA6, the relative accumulation of the molecules that bind s-WGA in the cyst wall was not dependent on the expression of GRA2. Our results suggest that GRA2-dependent and GRA2-independent mechanisms regulate the trafficking and accumulation of glycosylated molecules that colocalize in the cyst wall.IMPORTANCE Chronic Toxoplasma gondii infection is maintained in the central nervous system by thick-walled cysts. If host immunity wanes, cysts recrudesce and cause severe and often lethal toxoplasmic encephalitis. Currently, there are no therapies to eliminate cysts, and little biological information is available regarding cyst structure(s). Here, we investigated cyst wall molecules recognized by succinylated wheat germ agglutinin (s-WGA), a lectin that specifically binds to N-acetylglucosamine-decorated structures. N-Acetylglucosamine regulates cell signaling and plays structural roles at the cell surface in many organisms. The cyst wall and cyst matrix were heavily stained by s-WGA in mature cysts and were differentially stained during cyst development. The relative accumulation of molecules that bind to s-WGA in the cyst wall was not dependent on the expression of GRA2. Our findings suggest that glycosylated cyst wall molecules gain access to the cyst wall via GRA2-dependent and GRA2-independent mechanisms and colocalize in the cyst wall.

Analysis of the Effect of Increased α2,3-Sialylation on RTK Activation in MKN45 Gastric Cancer Spheroids Treated with Crizotinib

In the scenario of personalized medicine, targeted therapies are currently the focus of cancer drug development. These drugs can block the growth and spread of tumor cells by interfering with key molecules involved in malignancy, such as receptor tyrosine kinases (RTKs). MET and Recepteur d'Origine Nantais (RON), which are RTKs frequently overactivated in gastric cancer, are glycoprotein receptors whose activation have been shown to be modulated by the cellular glycosylation. In this work, we address the role of sialylation in gastric cancer therapy using an innovative 3D high-throughput cell culture methodology that mimics better the in vivo tumor features. We evaluate the response to targeted treatment of glycoengineered gastric cancer cell models overexpressing the sialyltransferases ST3GAL4 or ST3GAL6 by subjecting 3D spheroids to the tyrosine kinase inhibitor crizotinib. We show here that 3D spheroids of ST3GAL4 or ST3GAL6 overexpressing MKN45 gastric cancer cells are less affected by the inhibitor. In addition, we disclose a potential compensatory pathway via activation of the Insulin Receptor upon crizotinib treatment. Our results suggest that cell sialylation, in addition of being involved in tumor progression, could play a critical role in the response to tyrosine kinase inhibitors in gastric cancer.

Methods for Purifying Datura stramonium Agglutinin and Producing Recombinant Agglutinin Protein in a Heterologous Plant Host

Datura stramonium seeds contain at least three chitin-binding isolectins as homo- or heterodimers of A and B subunits. This lectin has been used for the detection and isolation of sugar chains with N-acetyllactosaminyl structures on highly branched N-glycans. In terms of future diagnostic use, the development of a recombinant lectin will be the most effective approach for producing homogeneous lectin preparations. This chapter presents details of the procedure used for lectin purification and also describes a method that can be used for producing active recombinant homodimeric BB-isolectin in Arabidopsis plants.

The Impact of Glycosylation of Osteopontin on Urinary Stone Formation

Osteopontin (OPN) is a matrix glycoprotein of urinary calculi. This study aims to identify the role of aberrant glycosylation of OPN in urolithiasis. We retrospectively measured urinary glycosylated OPN normalized by urinary full-length-OPN levels in 110 urolithiasis patients and 157 healthy volunteers and 21 patients were prospectively longitudinal follow-up during stone treatment. The urinary full-length-OPN levels were measured using enzyme-linked immunosorbent assay and glycosylated OPN was measured using a lectin array and lectin blotting. The assays were evaluated using the area under the receiver operating characteristics curve to discriminate stone forming urolithiasis patients. In the retrospective cohort, urinary Gal3C-S lectin reactive- (Gal3C-S-) OPN/full-length-OPN, was significantly higher in the stone forming urolithiasis patients than in the healthy volunteers (p < 0.0001), with good discrimination (AUC, 0.953), 90% sensitivity, and 92% specificity. The Lycopersicon esculentum lectin analysis of urinary full-length-OPN showed that urinary full-length-OPN in stone forming urolithiasis patients had a polyLacNAc structure that was not observed in healthy volunteers. In the prospective longitudinal follow-up study, 92.8% of the stone-free urolithiasis group had Gal3C-S-OPN/full-length-OPN levels below the cutoff value after ureteroscopic lithotripsy (URS), whereas 71.4% of the residual-stone urolithiasis group did not show decreased levels after URS. Therefore, Gal3C-S-OPN/full-length-OPN levels could be used as a urolithiasis biomarker.

Qualitative and quantitative alterations in intracellular and membrane glycoproteins maintain the balance between cellular senescence and human aging

Glycans are associated with and serve as biomarkers for various biological functions. We previously reported that cell surface sialylated glycoproteins of dermal fibroblasts decreased with cellular senescence and human aging. There is little information on the changes in glycoprotein expression and subcellular localization during the aging process. Here, we examined intracellular glycan profiles of fibroblasts undergoing cellular senescence and those derived from aging human subjects using lectin microarray analysis. We found a sequential change of the intracellular glycan profiles was little during cellular senescence. The intracellular glycans of cells derived from aged fetus and from elderly subjects showed similar localized patterns while repeating unsteady changes. The ratio of α2-3/2-6sialylated intracellular glycoproteins in total cell extracts increased, except for a part of α2-3sialylated O-glycans. These findings are in contrast to those for membrane glycoprotein, which decreased with aging. Interestingly, the ratio of increasing sialylated glycoproteins in the fetus-derived cells showing cellular senescence was similar to that in cells derived from the elderly. Thus, intracellular glycans may maintain cellular functions such as ubiquitin/proteasome-mediated degradation and/or autophagy during aging by contributing to the accumulation of intracellular glycosylated proteins. Our findings provide novel mechanistic insight into the molecular changes that occur during aging.

Altered Cell Surface N-Glycosylation of Resting and Activated T Cells in Systemic Lupus Erythematosus

Altered cell surface glycosylation in congenital and acquired diseases has been shown to affect cell differentiation and cellular responses to external signals. Hence, it may have an important role in immune regulation; however, T cell surface glycosylation has not been studied in systemic lupus erythematosus (SLE), a prototype of autoimmune diseases. Analysis of the glycosylation of T cells from patients suffering from SLE was performed by lectin-binding assay, flow cytometry, and quantitative real-time PCR. The results showed that resting SLE T cells presented an activated-like phenotype in terms of their glycosylation pattern. Additionally, activated SLE T cells bound significantly less galectin-1 (Gal-1), an important immunoregulatory lectin, while other lectins bound similarly to the controls. Differential lectin binding, specifically Gal-1, to SLE T cells was explained by the increased gene expression ratio of sialyltransferases and neuraminidase 1 (NEU1), particularly by elevated ST6 beta-galactosamide alpha-2,6-sialyltranferase 1 (ST6GAL1)/NEU1 and ST3 beta-galactoside alpha-2,3-sialyltransferase 6 (ST3GAL6)/NEU1 ratios. These findings indicated an increased terminal sialylation. Indeed, neuraminidase treatment of cells resulted in the increase of Gal-1 binding. Altered T cell surface glycosylation may predispose the cells to resistance to the immunoregulatory effects of Gal-1, and may thus contribute to the pathomechanism of SLE.

UDP-N-acetylglucosamine-dolichyl-phosphate N-acetylglucosaminephosphotransferase is indispensable for oogenesis, oocyte-to-embryo transition, and larval development of the nematode Caenorhabditis elegans

N-linked glycosylation of proteins is the most common post-translational modification of proteins. The enzyme UDP-N-acetylglucosamine-dolichyl-phosphate N-acetylglucosaminephosphotransferase (DPAGT1) catalyses the first step of N-glycosylation, and DPAGT1 knockout is embryonic lethal in mice. In this study, we identified the sole orthologue (algn-7) of the human DPAGT1 in the nematode C. elegans. The gene activity was disrupted by RNAi and deletion mutagenesis, which resulted in larval lethality, defects in oogenesis and oocyte-to-embryo transition. Endomitotic oocytes, abnormal fusion of pronuclei, abnormal AB cell rotation, disruption of permeation barriers of eggs, and abnormal expression of chitin and chitin synthase in oocytes and eggs were the typical phenotypes observed. The results indicate that N-glycosylation is indispensable for these processes. We further screened an N-glycosylated protein database of C. elegans, and identified 456 germline-expressed genes coding N-glycosylated proteins. By examining RNAi phenotypes, we identified five germline-expressed genes showing similar phenotypes to the algn-7 (RNAi) animals. They were ribo-1, stt-3, ptc-1, ptc-2, and vha-19. We identified known congenital disorders of glycosylation (CDG) genes (ribo-1 and stt-3) and a recently found CDG gene (vha-19). The results show that phenotype analyses using the nematode could be a powerful tool to detect new CDG candidate genes and their associated gene networks.

Exploring lectin-like activity of the S-layer protein of Lactobacillus acidophilus ATCC 4356

The surface layer (S-layer) protein of Lactobacillus acidophilus is a crystalline array of self-assembling, proteinaceous subunits non-covalently bound to the outmost bacterial cell wall envelope and is involved in the adherence of bacteria to host cells. We have previously described that the S-layer protein of L. acidophilus possesses anti-viral and anti-bacterial properties. In this work, we extracted and purified S-layer proteins from L. acidophilus ATCC 4356 cells to study their interaction with cell wall components from prokaryotic (i.e., peptidoglycan and lipoteichoic acids) and eukaryotic origin (i.e., mucin and chitin), as well as with viruses, bacteria, yeast, and blood cells. Using chimeric S-layer fused to green fluorescent protein (GFP) from different parts of the protein, we analyzed their binding capacity. Our results show that the C-terminal part of the S-layer protein presents lectin-like activity, interacting with different glycoepitopes. We further demonstrate that lipoteichoic acid (LTA) serves as an anchor for the S-layer protein. Finally, a structure for the C-terminal part of S-layer and possible binding sites were predicted by a homology-based model.

Increased galactose expression and enhanced clearance in patients with low von Willebrand factor

Glycan determinants on von Willebrand factor (VWF) play critical roles in regulating its susceptibility to proteolysis and clearance. Abnormal glycosylation has been shown to cause von Willebrand disease (VWD) in a number of different mouse models. However, because of the significant technical challenges associated with accurate assessment of VWF glycan composition, the importance of carbohydrates in human VWD pathogenesis remains largely unexplored. To address this, we developed a novel lectin-binding panel to enable human VWF glycan characterization. This methodology was then used to study glycan expression in a cohort of 110 patients with low VWF compared with O blood group-matched healthy controls. Interestingly, significant interindividual heterogeneity in VWF glycan expression was seen in the healthy control population. This variation included terminal sialylation and ABO(H) blood group expression on VWF. Importantly, we also observed evidence of aberrant glycosylation in a subgroup of patients with low VWF. In particular, terminal α(2-6)-linked sialylation was reduced in patients with low VWF, with a secondary increase in galactose (Gal) exposure. Furthermore, an inverse correlation between Gal exposure and estimated VWF half-life was observed in those patients with enhanced VWF clearance. Together, these findings support the hypothesis that loss of terminal sialylation contributes to the pathophysiology underpinning low VWF in at least a subgroup of patients by promoting enhanced clearance. In addition, alterations in VWF carbohydrate expression are likely to contribute to quantitative and qualitative variations in VWF levels in the normal population. This trial was registered at www.clinicaltrials.gov as #NCT03167320.

A complex between phosphatidylinositol 4-kinase IIα and integrin α3β1 is required for N-glycan sialylation in cancer cells

Aberrant N-glycan sialylation of glycoproteins is closely associated with malignant phenotypes of cancer cells and metastatic potential, which includes cell adhesion, migration, and growth. Recently, phosphatidylinositol 4-kinase IIα (PI4KIIα), which is localized to the trans-Golgi network, was identified as a regulator of Golgi phosphoprotein 3 (GOLPH3) and of vesicle transport in the Golgi apparatus. GOLPH3 is a target of PI4KIIα and helps anchor sialyltransferases and thereby regulates sialylation of cell surface receptors. However, how PI4KIIα-mediated sialyation of cell surface proteins is regulated remains unclear. In this study, using several cell lines, CRISPR/Cas9-based gene knockout and short hairpin RNA-mediated silencing, RT-PCR, lentivirus-mediated overexpression, and immunoblotting methods, we confirmed that PI4KIIα knockdown suppresses the sialylation of N-glycans on the cell surface, in Akt phosphorylation and activation, and integrin α3-mediated cell migration of MDA-MB-231 breast cancer cells. Interestingly, both integrin α3β1 and PI4KIIα co-localized to the trans-Golgi network, where they physically interacted with each other, and PI4KIIα specifically associated with integrin α3 but not α5. Furthermore, overexpression of both integrin α3β1 and PI4KIIα induced hypersialylation. Conversely, integrin α3 knockout significantly inhibited the sialylation of membrane proteins, such as the epidermal growth factor receptor, as well as in total cell lysates. These findings suggest that the malignant phenotype of cancer cells is affected by a sialylation mechanism that is regulated by a complex between PI4KIIα and integrin α3β1.

Subtle Differences in Symbiont Cell Surface Glycan Profiles Do Not Explain Species-Specific Colonization Rates in a Model Cnidarian-Algal Symbiosis

Mutualisms between cnidarian hosts and dinoflagellate endosymbionts are foundational to coral reef ecosystems. These symbioses are often re-established every generation with high specificity, but gaps remain in our understanding of the cellular mechanisms that control symbiont recognition and uptake dynamics. Here, we tested whether differences in glycan profiles among different symbiont species account for the different rates at which they initially colonize aposymbiotic polyps of the model sea anemone Aiptasia (Exaiptasia pallida). First, we used a lectin array to characterize the glycan profiles of colonizing Symbiodinium minutum (ITS2 type B1) and noncolonizing Symbiodinium pilosum (ITS2 type A2), finding subtle differences in the binding of lectins Euonymus europaeus lectin (EEL) and Urtica dioica agglutinin lectin (UDA) that distinguish between high-mannoside and hybrid-type protein linked glycans. Next, we enzymatically cleaved glycans from the surfaces of S. minutum cultures and followed their recovery using flow cytometry, establishing a 48-72 h glycan turnover rate for this species. Finally, we exposed aposymbiotic host polyps to cultured S. minutum cells masked by EEL or UDA lectins for 48 h, then measured cell densities the following day. We found no effect of glycan masking on symbiont density, providing further support to the hypothesis that glycan-lectin interactions are more important for post-phagocytic persistence of specific symbionts than they are for initial uptake. We also identified several methodological and biological factors that may limit the utility of studying glycan masking in the Aiptasia system.

Functional characterization of chitin-binding lectin from Solanum integrifolium containing anti-fungal and insecticidal activities

BACKGROUND

Along with the rapid development of glycomic tools, the study of lectin-carbohydrate interactions has expanded, opening the way for applications in the fields of analytic, diagnostic, and drug delivery. Chitin-binding lectins (CBLs) play roles in immune defense against chitin-containing pathogens. CBLs from species of the Solanaceae family, such as tomato, potato and jimsonweed, display different binding specificities to sugar chains containing poly-N-acetyllactosamine.

RESULTS

In this report, CBLs from Solanum integrifolium were isolated by ion exchange chromatography. The fractions showed hemagglutination activity (HA). The recombinant CBL in the 293F cell culture supernatant was able to inhibit the growth of Rhizoctonia solani and Colletotrichum gloeosporioide. Furthermore, the carbohydrate-binding property of CBLs was confirmed with the inhibition of HA. Binding of CBL to Spodoptera frugiperda (sf21) insect cells can partly be inhibited by N-Acetylglucosamine (GlcNAc), which is related to decrease mitochondrial membrane potential of sf21 cells.

CONCLUSIONS

The results showed that CBL exhibited antifungal properties and inhibited insect cell growth, which is directly correlated to the lectin-carbohydrate interaction. Further identification and characterization of CBLs will help to broaden their scope of application in plant defense and in biomedical applications.

In silico analysis of ChtBD3 domain to find its role in bacterial pathogenesis and beyond

Chitin binding domain 3, known by the acronym ChtBD3, is a domain in the enzymes and proteins of several pathogenic virus, bacteria and fungi. As this domain is evolutionarily-conserved in virulence factors of these infectious agents, its detailed investigation is of clinical interest. In this regard, the current in silico study analyzed ChtBD3 domain distribution in bacterial proteins present in publicly-available SMART (simple modular architecture research tool) database. Also, the co-occurring domains of ChtBD3 in the studied proteins were mapped to understand positional rearrangement of the domain and consequent functional diversity. Custom-made scripts were used to interpret the data and to derive patterns. As expected, interesting results were obtained. ChtBD3 domain co-occurred with other critical domains like peptidase, glycol_hydrolase, kinase, hemagglutinin-acting, collagen-binding, among others. The findings are expected to be of clinical relevance.