Potential Involvement of the South American Lungfish Intelectin-2 in Innate-Associated Immune Modulation.

Intelectins belong to a family of lectins with specific and transitory carbohydrate interaction capabilities. These interactions are related to the activity of agglutinating pathogens, as intelectins play a significant role in immunity. Despite the prominent immune defense function of intelectins, limited information about its structural characteristics and carbohydrate interaction properties is available. This study investigated an intelectin transcript identified in RNA-seq data obtained from the South American lungfish (Lepidosiren paradoxa), namely LpITLN2-B. The structural analyses predicted LpITLN2-B to be a homo-trimeric globular protein with the fibrinogen-like functional domain (FReD), exhibiting a molecular mass of 57 kDa. The quaternary structure is subdivided into three monomers, A, B, and C, and each domain comprises 11 ß-sheets: an anti-parallel ß-sheet, a ß-hairpin, and a disordered ß-sheet structure. Molecular docking demonstrates a significant interaction with disaccharides rather than monosaccharides. The preferential interaction with disaccharides highlights the potential interaction with pathogen molecules, such as LPS and Poly(I:C). The hemagglutination assay inhibited lectins activity, especially maltose and sucrose, highlighting lectin activity in L. paradoxa samples. Overall, our results show the potential relevance of LpITLN2-B in L. paradoxa immune defense against pathogens.

Galf-Specific Neolectins: Towards Promising Diagnostic Tools.

In the absence of naturally available galactofuranose-specific lectin, we report herein the bioengineering of GalfNeoLect, from the first cloned wild-type galactofuranosidase (Streptomyces sp. strain JHA19), which recognises and binds a single monosaccharide that is only related to nonmammalian species, usually pathogenic microorganisms. We kinetically characterised the GalfNeoLect to confirm attenuation of hydrolytic activity and used competitive inhibition assay, with close structural analogues of Galf, to show that it conserved interaction with its original substrate. We synthetised the bovine serum albumin-based neoglycoprotein (GalfNGP), carrying the multivalent Galf units, as a suitable ligand and high-avidity system for the recognition of GalfNeoLect which we successfully tested directly with the galactomannan spores of Aspergillus brasiliensis (ATCC 16404). Altogether, our results indicate that GalfNeoLect has the necessary versatility and plasticity to be used in both research and diagnostic lectin-based applications.

A common polymorphism in the Intelectin-1 gene influences mucus plugging in severe asthma.

By incompletely understood mechanisms, type 2 (T2) inflammation present in the airways of severe asthmatics drives the formation of pathologic mucus which leads to airway mucus plugging. Here we investigate the molecular role and clinical significance of intelectin-1 (ITLN-1) in the development of pathologic airway mucus in asthma. Through analyses of human airway epithelial cells we find that ITLN1 gene expression is highly induced by interleukin-13 (IL-13) in a subset of metaplastic MUC5AC+ mucus secretory cells, and that ITLN-1 protein is a secreted component of IL-13-induced mucus. Additionally, we find ITLN-1 protein binds the C-terminus of the MUC5AC mucin and that its deletion in airway epithelial cells partially reverses IL-13-induced mucostasis. Through analysis of nasal airway epithelial brushings, we find that ITLN1 is highly expressed in T2-high asthmatics, when compared to T2-low children. Furthermore, we demonstrate that both ITLN-1 gene expression and protein levels are significantly reduced by a common genetic variant that is associated with protection from the formation of mucus plugs in T2-high asthma. This work identifies an important biomarker and targetable pathways for the treatment of mucus obstruction in asthma.

The expression characteristic and prognostic role of Siglec-15 in lung adenocarcinoma.

Sialic acid-binding immunoglobulin-like lectin-15 (Siglec-15) has been identified as an immune suppressor and a promising candidate for immunotherapy of cancer management. However, the association between Siglec-15 expression and clinicopathological features of lung adenocarcinoma (LUAD), especially the prognostic role, is not fully elucidated. In this present study, a serial of bioinformatics analyses in both tissue and cell levels were conducted to provide an overview of Siglec-15 expression. Real-time quantitative PCR (qPCR) test, western blotting assay, and immunohistochemistry (IHC) analyses were conducted to evaluate the expression of Siglec-15 in LUAD. Survival analysis and Kaplan-Meier curve were employed to describe the prognostic parameters of LUAD. The results of bioinformatics analyses demonstrated the up-regulation of Siglec-15 expression in LUAD. The data of qPCR, western blotting, and IHC analyses further proved that the expression of Siglec-15 in LUAD tissues was significantly increased than that in noncancerous tissues. Moreover, the expression level of Siglec-15 protein in LUAD was substantially associated with TNM stage. LUAD cases with up-regulated Siglec-15 expression, positive N status, and advance TNM stage suffered a critical unfavorable prognosis. In conclusion, Siglec-15 could be identified as a novel prognostic biomarker in LUAD and targeting Siglec-15 may provide a promising strategy for LUAD immunotherapy.

Modulation of Campylobacter jejuni adhesion to biotic model surfaces by fungal lectins and protease inhibitors.

Campylobacter jejuni, a Gram-negative bacterium, is one of the most common causes of foodborne illness worldwide. Its adhesion mechanism is mediated by several bacterial factors, including flagellum, protein adhesins, lipooligosaccharides, proteases, and host factors, such as surface glycans on epithelial cells and mucins. Fungal lectins, specialized carbohydrate-binding proteins, can bind to specific glycans on host and bacterial cells and thus influence pathogenesis. In this study, we investigated the effects of fungal lectins and protease inhibitors on the adhesion of C. jejuni to model biotic surfaces (mucin, fibronectin, and collagen) and Caco-2 cells as well as the invasion of Caco-2 cells. The lectins Marasmius oreades agglutinin (MOA) and Laccaria bicolor tectonin 2 (Tec2) showed remarkable efficacy in all experiments. In addition, different pre-incubations of lectins with C. jejuni or Caco-2 cells significantly inhibited the ability of C. jejuni to adhere to and invade Caco-2 cells, but to varying degrees. Pre-incubation of Caco-2 cells with selected lectins reduced the number of invasive C. jejuni cells the most, while simultaneous incubation showed the greatest reduction in adherent C. jejuni cells. These results suggest that fungal lectins are a promising tool for the prevention and treatment of C. jejuni infections. Furthermore, this study highlights the potential of fungi as a rich reservoir for novel anti-adhesive agents.

Changes in serum immunoglobulin G glycosylation patterns for antiphospholipid syndrome patients with lectin microarray.

Antiphospholipid syndrome is a rare autoimmune disease characterized by persistent antiphospholipid antibodies. Immunoglobulin G plays a vital role in disease progression, with its structure and function affected by glycosylation. We aimed to investigate the changes in the serum immunoglobulin G glycosylation pattern in antiphospholipid syndrome patients. We applied lectin microarray on samples from 178 antiphospholipid syndrome patients, 135 disease controls (including Takayasu arteritis, rheumatoid arthritis and cardiovascular disease) and 100 healthy controls. Lectin blots were performed for validation of significant differences. Here, we show an increased immunoglobulin G-binding level of soybean agglutinin (p = 0.047, preferring N-acetylgalactosamine) in antiphospholipid syndrome patients compared with healthy and disease controls. Additionally, the immunoglobulin G from antiphospholipid syndrome patients diagnosed with pregnancy events had lower levels of fucosylation (p = 0.001, recognized by Lotus tetragonolobus) and sialylation (p = 0.030, recognized by Sambucus nigra I) than those with simple thrombotic events. These results suggest the unique serum immunoglobulin G glycosylation profile of antiphospholipid syndrome patients, which may inform future studies to design biomarkers for more accurate diagnosis of antiphospholipid syndrome and even for the prediction of clinical symptoms in patients.

Staphylococcus aureus skin colonization is mediated by SasG lectin variation.

Staphylococcus aureus causes the majority of skin and soft tissue infections, but this pathogen only transiently colonizes healthy skin. However, this transient skin exposure enables S. aureus to transition to infection. The initial adhesion of S. aureus to skin corneocytes is mediated by surface protein G (SasG). Here, phylogenetic analyses reveal the presence of two major divergent SasG alleles in S. aureus: SasG-I and SasG-II. Structural analyses of SasG-II identify a nonaromatic arginine in the binding pocket of the lectin subdomain that mediates adhesion to corneocytes. Atomic force microscopy and corneocyte adhesion assays indicate that SasG-II can bind to a broader variety of ligands than SasG-I. Glycosidase treatment results in different binding profiles between SasG-I and SasG-II on skin cells. In addition, SasG-mediated adhesion is recapitulated using differentiated N/TERT keratinocytes. Our findings indicate that SasG-II has evolved to adhere to multiple ligands, conferring a distinct advantage to S. aureus during skin colonization.

A Complex-Type N-Glycan-Specific Lectin Isolated from Green Alga Halimeda borneensis Exhibits Potent Anti-Influenza Virus Activity.

Marine algal lectins specific for high-mannose N-glycans have attracted attention because they strongly inhibit the entry of enveloped viruses, including influenza viruses and SARS-CoV-2, into host cells by binding to high-mannose-type N-glycans on viral surfaces. Here, we report a novel anti-influenza virus lectin (named HBL40), specific for complex-type N-glycans, which was isolated from a marine green alga, Halimeda borneensis. The hemagglutination activity of HBL40 was inhibited with both complex-type N-glycan and O-glycan-linked glycoproteins but not with high-mannose-type N-glycan-linked glycoproteins or any of the monosaccharides examined. In the oligosaccharide-binding experiment using 26 pyridylaminated oligosaccharides, HBL40 only bound to complex-type N-glycans with bi- and triantennary-branched sugar chains. The sialylation, core fucosylation, and the increased number of branched antennae of the N-glycans lowered the binding activity with HBL40. Interestingly, the lectin potently inhibited the infection of influenza virus (A/H3N2/Udorn/72) into NCI-H292 cells at IC50 of 8.02 nM by binding to glycosylated viral hemagglutinin (KD of 1.21 × 10-6 M). HBL40 consisted of two isolectins with slightly different molecular masses to each other that could be separated by reverse-phase HPLC. Both isolectins shared the same 16 N-terminal amino acid sequences. Thus, HBL40 could be useful as an antivirus lectin specific for complex-type N-glycans.

Microbial lectins as a potential therapeutics for the prevention of certain human diseases.

Lectins are protein or glycoprotein molecules with a specific ability to bind to carbohydrates. From viruses to mammals, they are found in various organisms and exhibit remarkable diverse structures and functions. They are significant contributors to defense mechanisms against microbial attacks in plants. They are also involved in functions such as controlling lymphocyte migration, regulating glycoprotein biosynthesis, cell-cell recognition, and embryonic development in animals. In addition, lectins serve as invaluable molecular tools in various biological and medical disciplines due to their reversible binding ability and enable the monitoring of cell membrane changes in physiological and pathological contexts. Microbial lectins, often referred to as adhesins, play an important role in microbial colonization, pathogenicity, and interactions among microorganisms. Viral lectins are located in the bilayered viral membrane, whereas bacterial lectins are found intracellularly and on the bacterial cell surface. Microfungal lectins are typically intracellular and have various functions in host-parasite interaction, and in fungal growth and morphogenesis. Although microbial lectin studies are less extensive than those of plants and animals, they provide insights into the infection mechanisms and potential interventions. Glycan specificity, essential functions in infectious diseases, and applications in the diagnosis and treatment of viral and bacterial infections are critical aspects of microbial lectin research. In this review, we will discuss the application and therapeutic potential of viral, bacterial and microfungal lectins.

The correlation between human seminal plasma sialoproteins and ejaculate parameters.

Sialic acids are negatively charged carbohydrates that are components of saccharide chains covalently linked to macromolecules. Sialylated glycoproteins are important for most biological processes, including reproduction, where they are associated with spermatogenesis, sperm motility, immune responses, and fertilization. Changes in the glycoprotein profile or sialylation in glycoproteins are likely to affect the quality of ejaculate. The aim of this study was to determine differences in the degree of sialylation between normozoospermic ejaculates and ejaculates with a pathological spermiogram using two lectins, Sambucus nigra (SNA) and Maackia amurensis (MAL II/MAA) recognizing α-2,6 or α-2,3 linkage of Sia to galactosyl residues. Our results show a close relationship between seminal plasma (SP) sialoproteins and the presence of anti-sperm antibodies in the ejaculate, apoptotic spermatozoa, and ejaculate quality. Using mass spectrometry, we identified SP sialoproteins such as, semenogelins, glycodelin, prolactin-inducible protein, lactotransferrin, and clusterin that are associated with spermatozoa and contribute to the modulation of the immune response and sperm apoptosis. Our findings suggest a correlation between the degree of SP glycoprotein sialylation and the existence of possible pathological states of spermatozoa and reproductive organs. Glycoproteins sialylation represents a potential parameter reflecting the overall quality of ejaculate and could potentially be utilised in diagnostics.

LectoScape: A Highly Multiplexed Imaging Platform for Glycome Analysis and Biomedical Diagnosis.

Glycosylation, a fundamental biological process, involves the attachment of glycans to proteins, lipids, and RNA, and it plays a crucial role in various biological pathways. It is of great significance to obtain the precise spatial distribution of glycosylation modifications at the cellular and tissue levels. Here, we introduce LectoScape, an innovative method enabling detailed imaging of tissue glycomes with up to 1 µm resolution through image mass cytometry (IMC). This method utilizes 12 distinct, nonoverlapping lectins selected via microarray technology, enabling the multiplexed detection of a wide array of glycans. Furthermore, we developed an efficient labeling strategy for these lectins. Crucially, our approach facilitates the concurrent imaging of diverse glycan motifs, including N-glycan and O-glycan, surpassing the capabilities of existing technologies. Using LectoScape, we have successfully delineated unique glycan structures in various cell types, enhancing our understanding of the glycan distribution across human tissues. Our method has identified specific glycan markers, such as α2,3-sialylated Galß1, 3GalNAc in O-glycan, and terminal GalNAc, as diagnostic indicators for cervical intraepithelial neoplasia. This highlights the potential of LectoScape in cancer diagnostics through the detection of abnormal glycosylation patterns.

Targeting SIGLEC15 as an emerging immunotherapy for anaplastic thyroid cancer.

Anaplastic thyroid carcinoma (ATC) is the most aggressive subtype of thyroid cancer with few effective therapies. Though immunotherapies such as targeting PD-1/PD-L1 axis have benefited patients with solid tumor, the druggable immune checkpoints are quite limited in ATC. In our study, we focused on the anti-tumor potential of sialic acid-binding Ig-like lectins (Siglecs) in ATC. Through screening by integrating microarray datasets including 216 thyroid-cancer tissues and single-cell RNA-sequencing, SIGLEC family members CD33, SIGLEC1, SIGLEC10 and SIGLEC15 were significantly overexpressed in ATC, among which SIGLEC15 increased highest and mainly expressed on cancer cells. SIGLEC15high ATC cells are characterized by high expression of serine protease PRSS23 and cancer stem cell marker CD44. Compared with SIGLEC15low cancer cells, SIGLEC15high ATC cells exhibited higher interaction frequency with tumor microenvironment cells. Further study showed that SIGLEC15high cancer cells mainly interacted with T cells by immunosuppressive signals such as MIF-TNFRSF14 and CXCL12-CXCR4. Notably, treatment of anti-SIGLEC15 antibody profoundly increased the cytotoxic ability of CD8+ T cells in a co-culture model and zebrafish-derived ATC xenografts. Consistently, administration of anti-SIGLEC15 antibody significantly inhibited tumor growth and prolonged mouse survival in an immunocompetent model of murine ATC, which was associated with increase of M1/M2, natural killer (NK) cells and CD8+ T cells, and decrease of myeloid-derived suppressor cells (MDSCs). SIGLEC15 inhibited T cell activation by reducing NFAT1, NFAT2, and NF-κB signals. Blocking SIGLEC15 increased the secretion of IFN-γ and IL-2 in vitro and in vivo. In conclusion, our finding demonstrates that SIGLEC15 is an emerging and promising target for immunotherapy in ATC.

Lectin binding to pectoral fin of neonate little skates reared under ambient and projected-end-of-century temperature regimes.

The glycosylation of macromolecules can vary both among tissue structural components and by adverse conditions, potentially providing an alternative marker of stress in organisms. Lectins are proteins that bind carbohydrate moieties and lectin histochemistry is a common method to visualize microstructures in biological specimens and diagnose pathophysiological states in human tissues known to alter glycan profiles. However, this technique is not commonly used to assess broad-spectrum changes in cellular glycosylation in response to environmental stressors. In addition, the binding of various lectins has not been studied in elasmobranchs (sharks, skates, and rays). We surveyed the binding tissue structure specificity of 14 plant-derived lectins, using both immunoblotting and immunofluorescence, in the pectoral fins of neonate little skates (Leucoraja erinacea). Skates were reared under present-day or elevated (+5°C above ambient) temperature regimes and evaluated for lectin binding as an indicator of changing cellular glycosylation and tissue structure. Lectin labeling was highly tissue and microstructure specific. Dot blots revealed no significant changes in lectin binding between temperature regimes. In addition, lectins only detected in the elevated temperature treatment were Canavalia ensiformis lectin (Concanavalin A) in spindle cells of muscle and Ricinus communis agglutinin in muscle capillaries. These results provide a reference for lectin labeling in elasmobranch tissue that may aid future investigations.

The essential malaria protein PfCyRPA targets glycans to invade erythrocytes.

Plasmodium falciparum is a human-adapted apicomplexan parasite that causes the most dangerous form of malaria. P. falciparum cysteine-rich protective antigen (PfCyRPA) is an invasion complex protein essential for erythrocyte invasion. The precise role of PfCyRPA in this process has not been resolved. Here, we show that PfCyRPA is a lectin targeting glycans terminating with α2-6-linked N-acetylneuraminic acid (Neu5Ac). PfCyRPA has a >50-fold binding preference for human, α2-6-linked Neu5Ac over non-human, α2-6-linked N-glycolylneuraminic acid. PfCyRPA lectin sites were predicted by molecular modeling and validated by mutagenesis studies. Transgenic parasite lines expressing endogenous PfCyRPA with single amino acid exchange mutants indicated that the lectin activity of PfCyRPA has an important role in parasite invasion. Blocking PfCyRPA lectin activity with small molecules or with lectin-site-specific monoclonal antibodies can inhibit blood-stage parasite multiplication. Therefore, targeting PfCyRPA lectin activity with drugs, immunotherapy, or a vaccine-primed immune response is a promising strategy to prevent and treat malaria.

Streptomyces umbrella toxin particles block hyphal growth of competing species.

Streptomyces are a genus of ubiquitous soil bacteria from which the majority of clinically utilized antibiotics derive1. The production of these antibacterial molecules reflects the relentless competition Streptomyces engage in with other bacteria, including other Streptomyces species1,2. Here we show that in addition to small-molecule antibiotics, Streptomyces produce and secrete antibacterial protein complexes that feature a large, degenerate repeat-containing polymorphic toxin protein. A cryo-electron microscopy structure of these particles reveals an extended stalk topped by a ringed crown comprising the toxin repeats scaffolding five lectin-tipped spokes, which led us to name them umbrella particles. Streptomyces coelicolor encodes three umbrella particles with distinct toxin and lectin composition. Notably, supernatant containing these toxins specifically and potently inhibits the growth of select Streptomyces species from among a diverse collection of bacteria screened. For one target, Streptomyces griseus, inhibition relies on a single toxin and that intoxication manifests as rapid cessation of vegetative hyphal growth. Our data show that Streptomyces umbrella particles mediate competition among vegetative mycelia of related species, a function distinct from small-molecule antibiotics, which are produced at the onset of reproductive growth and act broadly3,4. Sequence analyses suggest that this role of umbrella particles extends beyond Streptomyces, as we identified umbrella loci in nearly 1,000 species across Actinobacteria.

Serum Glycome as a Diagnostic and Prognostic Factor in Gestational Diabetes Mellitus.

Gestational diabetes mellitus (GDM) is a risk factor for both mother and fetus/neonate during and after the pregnancy. Inconsistent protocols and cumbersome screening procedures warrant the search for new and easily accessible biomarkers. We investigated a potential of serum N-glycome to differentiate between healthy pregnant women (n = 49) and women with GDM (n = 53) using a lectin-based microarray and studied the correlation between the obtained data and parameters of glucose and lipid metabolism. Four out of 15 lectins used were able to detect the differences between the control and GDM groups in fucosylation, terminal galactose/N-acetylglucosamine (Gal/GlcNAc), presence of Galα1,4Galß1,4Glc (Gb3 antigen), and terminal α2,3-sialylation with AUC values above 60%. An increase in the Gb3 antigen and α2,3-sialylation correlated positively with GDM, whereas the amount of fucosylated glycans correlated negatively with the content of terminal Gal/GlcNAc. The content of GlcNAc oligomers correlated with the highest number of blood analytes, indices, and demographic characteristics, but failed to discriminate between the groups. The presence of terminal Gal residues correlated positively with the glucose levels and negatively with the LDL levels in the non-GDM group only. The results suggest fucosylation, terminal galactosylation, and the presence of Gb3 antigen as prediction markers of GDM.

Transient Binding Dynamics of Complement System Pattern Recognition Molecules on Pathogens.

Previous studies of pattern recognition molecules (PRMs) of the complement system have revealed difficulties in observing binding on pathogens such as Aspergillus fumigatus and Escherichia coli, despite complement deposition indicative of classical and lectin pathway activation. Thus, we investigated the binding dynamics of PRMs of the complement system, specifically C1q of the classical pathway and mannose-binding lectin (MBL) of the lectin pathway. We observed consistently increasing deposition of essential complement components such as C4b, C3b, and the terminal complement complex on A. fumigatus and E. coli. However, C1q and MBL binding to the surface rapidly declined during incubation after just 2-4 min in 10% plasma. The detachment of C1q and MBL can be linked to complement cascade activation, as the PRMs remain bound in the absence of plasma. The dissociation and the fate of C1q and MBL seem to have different mechanistic functions. Notably, C1q dynamics were associated with local C1 complex activation. When C1s was inhibited in plasma, C1q binding not only remained high but further increased over time. In contrast, MBL binding was inversely correlated with total and early complement activation due to MBL binding being partially retained by complement inhibition. Results indicate that detached MBL might be able to functionally rebind to A. fumigatus. In conclusion, these results reveal a (to our knowledge) novel "hit-and-run" complement-dependent PRM dynamic mechanism on pathogens. These dynamics may have profound implications for host defense and may help increase the functionality and longevity of complement-dependent PRMs in circulation.

Liquid Glycan Array.

The M13 phage platform is a stable and monodisperse nanoscale carrier, which can be modified with different molecules by chemical conjugation strategies. Here, we describe M13 phage acylated on pVIII protein with a dibenzocyclooctyne reacting with azido glycan to yield 30-1500 copy numbers of glycan per phage and monitored by MALDI-TOF spectrometry to generate multivalent glycoconjugates that contain desired densities of glycans. We prepared the liquid glycan arrays (LiGA) such that both the structure and density of glycans were encoded in the DNA of the bacteriophage. The LiGA can be used to validate the binding properties of glycans to purified lectins and explore the effect of glycan density on such binding. From a mixture of multivalent glycan probes, LiGAs can also identify the glycoconjugates with optimal avidity necessary for binding to lectins on living cells in vitro and live animals in vivo.

Targeted and Self-Adjuvated Nanoglycovaccine Candidate for Cancer Immunotherapy.

Advanced-stage solid primary tumors and metastases often express mucin 16 (MUC16), carrying immature glycans such as the Tn antigen, resulting in specific glycoproteoforms not found in healthy human tissues. This presents a valuable approach for designing targeted therapeutics, including cancer glycovaccines, which could potentially promote antigen recognition and foster the immune response to control disease spread and prevent relapse. In this study, we describe an adjuvant-free poly(lactic-co-glycolic acid) (PLGA)-based nanoglycoantigen delivery approach that outperforms conventional methods by eliminating the need for protein carriers while exhibiting targeted and adjuvant properties. To achieve this, we synthesized a library of MUC16-Tn glycoepitopes through single-pot enzymatic glycosylation, which were then stably engrafted onto the surface of PLGA nanoparticles, generating multivalent constructs that better represent cancer molecular heterogeneity. These glycoconstructs demonstrated affinity for Macrophage Galactose-type Lectin (MGL) receptor, known to be highly expressed by immature antigen-presenting cells, enabling precise targeting of immune cells. Moreover, the glycopeptide-grafted nanovaccine candidate displayed minimal cytotoxicity and induced the activation of dendritic cells in vitro, even in the absence of an adjuvant. In vivo, the formulated nanovaccine candidate was also nontoxic and elicited the production of IgG specifically targeting MUC16 and MUC16-Tn glycoproteoforms in cancer cells and tumors, offering potential for precise cancer targeting, including targeted immunotherapies.

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.