Exploring lectin-glycan interactions to combat COVID-19: Lessons acquired from other enveloped viruses

Molecular basis of N-glycan recognition by pradimicin a and its potential as a SARS-CoV-2 entry inhibitor

Virus entry inhibitors are emerging as an attractive class of therapeutics for the suppression of viral transmission. Naturally occurring pradimicin A (PRM-A) has received particular attention as the first-in-class entry inhibitor that targets N-glycans present on viral surface. Despite the uniqueness of its glycan-targeted antiviral activity, there is still limited knowledge regarding how PRM-A binds to viral N-glycans. Therefore, in this study, we performed binding analysis of PRM-A with synthetic oligosaccharides that reflect the structural motifs characteristic of viral N-glycans. Binding assays and molecular modeling collectively suggest that PRM-A preferentially binds to branched oligomannose motifs of N-glycans via simultaneous recognition of two mannose residues at the non-reducing ends. We also demonstrated, for the first time, that PRM-A can effectively inhibit severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in vitro. Significantly, the anti-SARS-CoV-2 effect of PRM-A is attenuated in the presence of the synthetic branched oligomannose, suggesting that the inhibition of SARS-CoV-2 infection is due to the interaction of PRM-A with the branched oligomannose-containing N-glycans. These data provide essential information needed to understand the antiviral mechanism of PRM-A and suggest that PRM-A could serve as a candidate SARS-CoV-2 entry inhibitor targeting N-glycans.

Mannose-specific plant and microbial lectins as antiviral agents: A review

Lectins are non-immunological carbohydrate-binding proteins classified on the basis of their structure, origin, and sugar specificity. The binding specificity of such proteins with the surface glycan moiety determines their activity and clinical applications. Thus, lectins hold great potential as diagnostic and drug discovery agents and as novel biopharmaceutical products. In recent years, significant advancements have been made in understanding plant and microbial lectins as therapeutic agents against various viral diseases. Among them, mannose-specific lectins have being proven as promising antiviral agents against a variety of viruses, such as HIV, Influenza, Herpes, Ebola, Hepatitis, Severe Acute Respiratory Syndrome Coronavirus-1 (SARS-CoV-1), Middle Eastern Respiratory Syndrome Coronavirus (MERS-CoV) and most recent Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). The binding of mannose-binding lectins (MBLs) from plants and microbes to high-mannose containing N-glycans (which may be simple or complex) of glycoproteins found on the surface of viruses has been found to be highly specific and mainly responsible for their antiviral activity. MBLs target various steps in the viral life cycle, including viral attachment, entry and replication. The present review discusses the brief classification and structure of lectins along with antiviral activity of various mannose-specific lectins from plants and microbial sources and their diagnostic and therapeutic applications against viral diseases.

Structural and non-structural proteins in SARS-CoV-2: potential aspects to COVID-19 treatment or prevention of progression of related diseases

Coronavirus disease 2019 (COVID-19) is caused by a new member of the Coronaviridae family known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). There are structural and non-structural proteins (NSPs) in the genome of this virus. S, M, H, and E proteins are structural proteins, and NSPs include accessory and replicase proteins. The structural and NSP components of SARS-CoV-2 play an important role in its infectivity, and some of them may be important in the pathogenesis of chronic diseases, including cancer, coagulation disorders, neurodegenerative disorders, and cardiovascular diseases. The SARS-CoV-2 proteins interact with targets such as angiotensin-converting enzyme 2 (ACE2) receptor. In addition, SARS-CoV-2 can stimulate pathological intracellular signaling pathways by triggering transcription factor hypoxia-inducible factor-1 (HIF-1), neuropilin-1 (NRP-1), CD147, and Eph receptors, which play important roles in the progression of neurodegenerative diseases like Alzheimer's disease, epilepsy, and multiple sclerosis, and multiple cancers such as glioblastoma, lung malignancies, and leukemias. Several compounds such as polyphenols, doxazosin, baricitinib, and ruxolitinib could inhibit these interactions. It has been demonstrated that the SARS-CoV-2 spike protein has a stronger affinity for human ACE2 than the spike protein of SARS-CoV, leading the current study to hypothesize that the newly produced variant Omicron receptor-binding domain (RBD) binds to human ACE2 more strongly than the primary strain. SARS and Middle East respiratory syndrome (MERS) viruses against structural and NSPs have become resistant to previous vaccines. Therefore, the review of recent studies and the performance of current vaccines and their effects on COVID-19 and related diseases has become a vital need to deal with the current conditions. This review examines the potential role of these SARS-CoV-2 proteins in the initiation of chronic diseases, and it is anticipated that these proteins could serve as components of an effective vaccine or treatment for COVID-19 and related diseases. Video Abstract.

Plants as Biofactories for Therapeutic Proteins and Antiviral Compounds to Combat COVID-19

The outbreak of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) had a profound impact on the world's health and economy. Although the end of the pandemic may come in 2023, it is generally believed that the virus will not be completely eradicated. Most likely, the disease will become an endemicity. The rapid development of vaccines of different types (mRNA, subunit protein, inactivated virus, etc.) and some other antiviral drugs (Remdesivir, Olumiant, Paxlovid, etc.) has provided effectiveness in reducing COVID-19's impact worldwide. However, the circulating SARS-CoV-2 virus has been constantly mutating with the emergence of multiple variants, which makes control of COVID-19 difficult. There is still a pressing need for developing more effective antiviral drugs to fight against the disease. Plants have provided a promising production platform for both bioactive chemical compounds (small molecules) and recombinant therapeutics (big molecules). Plants naturally produce a diverse range of bioactive compounds as secondary metabolites, such as alkaloids, terpenoids/terpenes and polyphenols, which are a rich source of countless antiviral compounds. Plants can also be genetically engineered to produce valuable recombinant therapeutics. This molecular farming in plants has an unprecedented opportunity for developing vaccines, antibodies, and other biologics for pandemic diseases because of its potential advantages, such as low cost, safety, and high production volume. This review summarizes the latest advancements in plant-derived drugs used to combat COVID-19 and discusses the prospects and challenges of the plant-based production platform for antiviral agents.

Molecular Cloning and Characteristics of a Lectin from the Bivalve Glycymeris yessoensis

C-type lectins (CTLs) are a family of carbohydrate-binding proteins that mediate multiple biological events, including adhesion between cells, the turnover of serum glycoproteins, and innate immune system reactions to prospective invaders. Here, we describe the cDNA cloning of lectin from the bivalve Glycymeris yessoensis (GYL), which encodes 161 amino acids and the C-type carbohydrate recognition domain (CRD) with EPN and WND motifs. The deduced amino acid sequence showed similarity to other CTLs. GYL is a glycoprotein containing two N-glycosylation sites per subunit. N-glycans are made up of xylose, mannose, D-glucosamine, 3-O-methylated galactose, D-quinovoses, and 3-O-methylated 6-deoxy-D-glucose. The potential CRD tertiary structure of the GYL adopted CTL-typical long-form double-loop structure and included three disulfide bridges at the bases of the loops. Additionally, when confirming the GYL sequence, eight isoforms of this lectin were identified. This fact indicates the presence of a multigene family of GYL-like C-type lectins in the bivalve G. yessoensis. Using the glycan microarray approach, natural carbohydrate ligands were established, and the glycotope for GYL was reconstructed as "Galβ1-4GlcNAcβ obligatory containing an additional fragment", like a sulfate group or a methyl group of fucose or N-acetylgalactosamine residues.

Lectin Analysis of SARS-CoV-2-Positive Nasopharyngeal Samples Using GLYcoPROFILE® Technology Platform

Nasopharyngeal samples are currently accepted as the standard diagnostic samples for nucleic acid amplification testing and antigenic testing for the SARS-CoV-2 virus. In addition to the diagnostic capacity of SARS-CoV-2-positive crude nasopharyngeal samples, their qualitative potential for direct glycan-specific analysis, in order to uncover unique glycol profiles, was assessed. In this study we provide glycan characterization of SARS-CoV-2-positive and -negative nasopharyngeal samples directly from lectin interactions. Although with limited throughput, this study evaluated the clinical sensitivity and specificity of the GLYcoPROFILE® technology platformon45crude nasopharyngeal samples collected between November 2020 and April 2022. Each GLYcoPROFILE® of 39 SARS-CoV-2-positive samples was compared toglycoprofiling on a panel of 10 selected lectins and the results were paralleled with SARS-CoV-2-negative samples’ results. The GLYcoPROFILE® showed a clear distinction between positive and negative samples with WFA, GSL-II, PHA-L (GlcNAc-specific) and BPA (GalNAc-specific) highlighted as relevant lectins in SARS-CoV-2-positive samples. In addition, a significant, positive statistical correlation was found for these lectins (p < 0.01).

In-silico structural inhibition of ACE-2 binding site of SARS-CoV-2 and SARS-CoV-2 Omicron spike protein by lectin antiviral dyad system to treat COVID-19

Spike glycoprotein of SARS-CoV-2 binds ACE-2 receptors via its receptor-binding-domain (RBD) and mediates virus-to-host cell fusion. Recently emerged omicron variant of SARS-CoV-2 possess around 30 mutations in spike protein where N501Y tremendously increases viral infectivity and transmission. Lectins interact with glycoproteins and mediate innate immunity displaying antiviral, antibacterial and anticarcinogenic properties. In this study, we analysed the potential of lectin, and lectin-antibody (spike-specific) complex to inhibit the ACE-2 binding site of wild and N501Y mutated spike protein by utilizing in-silico molecular docking and simulation approach. Docking of lectin at reported ACE-2 binding spike-RBD residues displayed the ZDock scores of 1907 for wild and 1750 for N501Y mutated spike-RBD. Binding of lectin with antibody to form proposed dyad complex gave ZDock score of 1174 revealing stable binding. Docking of dyad complex with wild and N501Y mutated spike-RBD, at lectin and antibody individually, showed high efficiency binding hence, effective structural inhibition of spike-RBD. MD simulation of 100ns of each complex proved high stability of complexes with RMSD values ranging from 0.2 -1.5nm. Consistent interactions of lead ACE-2 binding spike residues with lectin during simulation disclosed efficient structural inhibition by lectin against formation of spike RBD-ACE-2 complex.Hence, lectins along with their ability to induce innate immunity against spike glycoprotein can structurally inhibit the spike-RBD when given as lectin-antibody dyad system and thus can be developed into a dual effect treatment against COVID-19. Moreover, the high binding specificity of this system with spike-RBD can be exploited for development of diagnostic and drug-delivery systems.

Lectins from plant and algae act as anti-viral against HIV, influenza and coronaviruses

BACKGROUND

Carbohydrate-lectin interactions are extremely specific as the lectin is capable of recognising monomeric and oligomeric sugars in a reversible manner. It has been known for a long time that lectins have antibacterial, antifungal, and insecticidal activities. Recently, it has been reported that many lectins can prevent the virus growth by interacting with the viral envelop surface glycoprotein. Spike protein, which is found on the surface of some enveloped viruses, is heavily mannosylated and will have strong affinity for mannose specific lectins. According to the findings, lectins have a high binding affinity for the glycans of the SARS-CoV-2 spike glycoprotein, which contains N-glycosylation sites. As a result, various lectins are being researched and developed as anti-viral agents.

RESULTS

According to our in silico studies, the amino acid residues Asn487, Tyr489, Gln493, Lys417, and Tyr505 of the receptor binding domain (RBD) of SARS-CoV-2 formed an interaction with the model lectin Lablab purpureus lectin. Similar interaction for SARS-CoV-2 spike protein was observed with Griffithsin lectin (algal source) as well. These observations demonstrate that lectins could be one of the potential molecules for neutralising coronavirus infection.

CONCLUSION

This review focuses on anti-viral lectins isolated and characterized from plants and algae (last 5 years) and showed anti-viral properties against HIV, Influenza, and coronaviruses.

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).

A Novel Plant Lectin, NTL-125, Interferes with SARS-CoV-2 Interaction with hACE2

COVID-19 caused by SARS-CoV-2 virus has had profound impact on the world in the past two years. Intense research is going on to find effective drugs to combat the disease. Over the past year several vaccines were approved for immunization. But SARS-CoV-2 being an RNA virus is continuously mutating to generate new variants, some of which develop features of immune escape. This raised serious doubts over the long-term efficacy of the vaccines. We have identified a unique mannose binding plant lectin from Narcissus tazetta bulb, NTL-125, which effectively inhibits SARS-CoV-2 replication in Vero-E6 cell line. In silico docking studies revealed that NTL-125 has strong affinity to viral Spike RBD protein, preventing it from attaching to hACE2 receptor, the gateway to cellular entry. Binding analyses revealed that all the mutant variants of Spike protein also have stronger affinity for NTL-125 than hACE2. The unique α-helical tail of NTL-125 plays most important role in binding to RBD of Spike. NTL-125 also interacts effectively with some glycan moieties of S-protein in addition to amino acid residues adding to the binding strength. Thus, NTL-125 is a highly potential antiviral compound of natural origin against SARS-CoV-2 and may serve as an important therapeutic for management of COVID-19.

Plant lectins as prospective antiviral biomolecules in the search for COVID-19 eradication strategies

Lectins or clusters of carbohydrate-binding proteins of non-immune origin are distributed chiefly in the Plantae. Lectins have potent anti-infectivity properties for several RNA viruses including SARS-CoV-2. The primary purpose of this review is to review the ability of lectins mediated potential biotherapeutic and bioprophylactic strategy against coronavirus causing COVID-19. Lectins have binding affinity to the glycans of SARS-COV-2 Spike glycoprotein that has N-glycosylation sites. Apart from this, the complement lectin pathway is a "first line host defense" against the viral infection that is activated by mannose-binding lectins. Mannose-binding lectins deficiency in serum influences innate immunity of the host and facilitates infectious diseases including COVID-19. Our accumulated evidence obtained from scientific databases particularly PubMed and Google Scholar databases indicate that mannose-specific/mannose-binding lectins (MBL) have potent efficacies like anti-infectivity, complement cascade induction, immunoadjuvants, DC-SIGN antagonists, or glycomimetic approach, which can prove useful in the strategy of COVID-19 combat along with the glycobiological aspects of SARS-CoV-2 infections and antiviral immunity. For example, plant-derived mannose-specific lectins BanLac, FRIL, Lentil, and GRFT from red algae can inhibit and neutralize SARS-CoV-2 infectivity, as confirmed with in-vitro, in-vivo, and in-silico assessments. Furthermore, Bangladesh has a noteworthy resource of antiviral medicinal plants as well as plant lectins. Intensifying research on the antiviral plant lectins, adopting a glyco-biotechnological approach, and with deeper insights into the "glycovirological" aspects may result in the designing of alternative and potent blueprints against the 21st century's biological pandemic of SARS-CoV-2 causing COVID-19.

Research advances and prospects of legume lectins

Lectins are widely distributed proteins having ability of binding selectively and reversibly with carbohydrates moieties and glycoconjugates. Although lectins have been reported from different biological sources, the legume lectins are the best-characterized family of plant lectins. Legume lectins are a large family of homologous proteins with considerable similarity in amino acid sequence and their tertiary structures. Despite having strong sequence conservation, these lectins show remarkable variability in carbohydrate specificity and quaternary structures. The ability of legume lectins in recognizing glycans and glycoconjugates on cells and other intracellular structures make them a valuable research tool in glycomic research. Due to variability in binding with glycans, glycoconjugates and multiple biological functions, legume lectins are the subject of intense research for their diverse application in different fields such as glycobiology, biomedical research and crop improvement. The present review specially focuses on structural and functional characteristics of legume lectins along with their potential areas of application.

The glycosylation in SARS-CoV-2 and its receptor ACE2

Coronavirus disease 2019 (COVID-19), a highly infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has infected more than 235 million individuals and led to more than 4.8 million deaths worldwide as of October 5 2021. Cryo-electron microscopy and topology show that the SARS-CoV-2 genome encodes lots of highly glycosylated proteins, such as spike (S), envelope (E), membrane (M), and ORF3a proteins, which are responsible for host recognition, penetration, binding, recycling and pathogenesis. Here we reviewed the detections, substrates, biological functions of the glycosylation in SARS-CoV-2 proteins as well as the human receptor ACE2, and also summarized the approved and undergoing SARS-CoV-2 therapeutics associated with glycosylation. This review may not only broad the understanding of viral glycobiology, but also provide key clues for the development of new preventive and therapeutic methodologies against SARS-CoV-2 and its variants.

SARS-CoV-2 spike protein: pathogenesis, vaccines, and potential therapies

PURPOSE

COVID-19 pandemic has emerged as a result of infection by the deadly pathogenic severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), causing enormous threats to humans. Coronaviruses are distinguished by a clove-like spike (S) protein, which plays a key role in viral pathogenesis, evolutions, and transmission. The objectives of this study are to investigate the distinctive structural features of SARS-CoV-2 S protein, its essential role in pathogenesis, and its use in the development of potential therapies and vaccines.

METHODOLOGY

A literature review was conducted to summarize, analyze, and interpret the available scientific data related to SARS-CoV-2 S protein in terms of characteristics, vaccines development and potential therapies.

RESULTS

The data indicate that S protein subunits and their variable conformational states significantly affect the virus pathogenesis, infectivity, and evolutionary mutation. A considerable number of potential natural and synthetic therapies were proposed based on S protein. Additionally, neutralizing antibodies were recently approved for emergency use. Furthermore, several vaccines utilizing the S protein were developed.

CONCLUSION

A better understanding of S protein features, structure and mutations facilitate the recognition of the importance of SARS-CoV-2 S protein in viral infection, as well as the development of therapies and vaccines. The efficacy and safety of these therapeutic compounds and vaccines are still controversial. However, they may potentially reduce or prevent SARS-CoV-2 infection, leading to a significant reduction of the global health burden of this pandemic.

Characteristics of SARS-CoV2 that may be useful for nanoparticle pulmonary drug delivery

As a non-invasive method of local and systemic drug delivery, the administration of active pharmaceutical ingredients (APIs) via the pulmonary route represents an ideal approach for the therapeutic treatment of pulmonary diseases. The pulmonary route provides a number of advantages, including the rapid absorption which results from a high level of vascularisation over a large surface area and the successful avoidance of first-pass metabolism. Aerosolization of nanoparticles (NPs) is presently under extensive investigation and exhibits a high potential for targeted delivery of therapeutic agents for the treatment of a wide range of diseases. NPs need to possess specific characteristics to facilitate their transport along the pulmonary tract and appropriately overcome the barriers presented by the pulmonary system. The most challenging aspect of delivering NP-based drugs via the pulmonary route is developing colloidal systems with the optimal physicochemical parameters for inhalation. The physiochemical properties of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) have been investigated as a template for the synthesis of NPs to assist in the formulation of virus-like particles (VLPs) for pharmaceutical delivery, vaccine production and diagnosis assays.

C-type lectins and extracellular vesicles in virus-induced NETosis

Dysregulated formation of neutrophil extracellular traps (NETs) is observed in acute viral infections. Moreover, NETs contribute to the pathogenesis of acute viral infections, including those caused by the dengue virus (DV) and severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Furthermore, excessive NET formation (NETosis) is associated with disease severity in patients suffering from SARS-CoV-2-induced multiple organ injuries. Dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) and other members of C-type lectin family (L-SIGN, LSECtin, CLEC10A) have been reported to interact with viral glycans to facilitate virus spreading and exacerbates inflammatory reactions. Moreover, spleen tyrosine kinase (Syk)-coupled C-type lectin member 5A (CLEC5A) has been shown as the pattern recognition receptor for members of flaviviruses, and is responsible for DV-induced cytokine storm and Japanese encephalomyelitis virus (JEV)-induced neuronal inflammation. Moreover, DV activates platelets via CLEC2 to release extracellular vesicles (EVs), including microvesicles (MVs) and exosomes (EXOs). The DV-activated EXOs (DV-EXOs) and MVs (DV-MVs) stimulate CLEC5A and Toll-like receptor 2 (TLR2), respectively, to enhance NET formation and inflammatory reactions. Thus, EVs from virus-activated platelets (PLT-EVs) are potent endogenous danger signals, and blockade of C-type lectins is a promising strategy to attenuate virus-induced NETosis and intravascular coagulopathy.

Inhibition of Protein N-Glycosylation Blocks SARS-CoV-2 Infection

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) extensively N-glycosylates its spike proteins, which are necessary for host cell invasion and the target of both vaccines and immunotherapies. These N-glycans are predicted to modulate spike binding to the host receptor by stabilizing its open conformation and host immunity evasion. Here, we investigated the essentiality of both the host N-glycosylation pathway and SARS-CoV-2 N-glycans for infection. Ablation of host N-glycosylation using RNA interference or inhibitors, including FDA-approved drugs, reduced the spread of the infection, including that of variants B.1.1.7 (Alpha), B.1.351 (Beta), P.1 (Gamma) and B.1.617.2 (Delta). Under these conditions, cells produced fewer virions and some completely lost their infectivity. Furthermore, partial enzymatic deglycosylation of intact virions showed that surface-exposed N-glycans are critical for cell invasion. Altogether, we propose protein N-glycosylation as a targetable pathway with clinical potential for treatment of COVID-19. IMPORTANCE The coronavirus SARS-CoV-2 uses its spike surface proteins to infect human cells. Spike proteins are heavily modified with several N-glycans, which are predicted to modulate their function. In this work, we show that interfering with either the synthesis or attachment of spike N-glycans significantly reduces the spread of SARS-CoV-2 infection in vitro, including that of several variants. As new SARS-CoV-2 variants, with various degrees of resistance against current vaccines, are likely to continue appearing, halting virus glycosylation using repurposed human drugs could result in a complementary strategy to reducing the spread of COVID-19 worldwide.

Research advances and prospects of legume lectins

Lectins are widely distributed proteins having ability of binding selectively and reversibly with carbohydrates moieties and glycoconjugates. Although lectins have been reported from different biological sources, the legume lectins are the best-characterized family of plant lectins. Legume lectins are a large family of homologous proteins with considerable similarity in amino acid sequence and their tertiary structures. Despite having strong sequence conservation, these lectins show remarkable variability in carbohydrate specificity and quaternary structures. The ability of legume lectins in recognizing glycans and glycoconjugates on cells and other intracellular structures make them a valuable research tool in glycomic research. Due to variability in binding with glycans, glycoconjugates and multiple biological functions, legume lectins are the subject of intense research for their diverse application in different fields such as glycobiology, biomedical research and crop improvement. The present review specially focuses on structural and functional characteristics of legume lectins along with their potential areas of application.