Search Results (11)

Microvirin is a lectin molecule known to have monovalent interaction with glycoprotein gp120. A previously reported high-resolution structural analysis defines the mannobiose-binding cavity of Microvirin. Nonetheless, structure does not directly define the energetics of binding contributions of protein contact residues. To better understand the nature of the MVN-Env glycan interaction, we used mutagenesis to evaluate the residue contributions to the mannobiose binding site of MVN that are important for Env gp120 glycan binding. MVN binding site amino acid residues were individually replaced by alanine, and the resulting purified recombinant MVN variants were examined for gp120 interaction using competition Enzyme-Linked Immunosorbent Assay (ELISA), biosensor surface plasmon resonance, calorimetry, and virus neutralization assays. Our findings highlight the role of both uncharged polar and non-polar residues in forming a hydropathic recognition site for the monovalent glycan engagement of Microvirin, in marked contrast to the charged residues utilized in the two Cyanovirin-N (CVN) glycan-binding sites. Full article

The emergence of COVID-19 continues to pose severe threats to global public health. The pandemic has infected over 171 million people and claimed more than 3.5 million lives to date. We investigated the binding potential of antiviral cyanobacterial proteins including cyanovirin-N, scytovirin and phycocyanin with fundamental proteins involved in attachment and replication of SARS-CoV-2. Cyanovirin-N displayed the highest binding energy scores (−16.8 ± 0.02 kcal/mol, −12.3 ± 0.03 kcal/mol and −13.4 ± 0.02 kcal/mol, respectively) with the spike protein, the main protease (M^pro) and the papainlike protease (PL^pro) of SARS-CoV-2. Cyanovirin-N was observed to interact with the crucial residues involved in the attachment of the human ACE2 receptor. Analysis of the binding affinities calculated employing the molecular mechanics-Poisson–Boltzmann surface area (MM-PBSA) approach revealed that all forms of energy, except the polar solvation energy, favourably contributed to the interactions of cyanovirin-N with the viral proteins. With particular emphasis on cyanovirin-N, the current work presents evidence for the potential inhibition of SARS-CoV-2 by cyanobacterial proteins, and offers the opportunity for in vitro and in vivo experiments to deploy the cyanobacterial proteins as valuable therapeutics against COVID-19. Full article

Glycan-targeting antibodies and pseudo-antibodies have been extensively studied for their stoichiometry, avidity, and their interactions with the rapidly modifying glycan shield of influenza A. Broadly neutralizing antiviral agents bind in the same order when they neutralize enveloped viruses regardless of the location of epitopes to the host receptor binding site. Herein, we investigated the binding of cyanovirin-N (CV–N) to surface-expressed glycoproteins such as those of human immunodeficiency virus (HIV) gp120, hemagglutinin (HA), and Ebola (GP)1,2 and compared their binding affinities with the binding response to the trimer-folded gp140 using surface plasmon resonance (SPR). Binding-site knockout variants of an engineered dimeric CV–N molecule (CVN2) revealed a binding affinity that correlated with the number of (high-) affinity binding sites. Binding curves were specific for the interaction with N-linked glycans upon binding with two low-affinity carbohydrate binding sites. This biologically active assembly of a domain-swapped CVN2, or monomeric CV–N, bound to HA with a maximum K_D of 2.7 nM. All three envelope spike proteins were recognized at a nanomolar K_D, whereas binding to HIV neutralizing 2G12 by targeting HA and Ebola GP1,2 was measured in the µM range and specific for the bivalent binding scheme in SPR. In conclusion, invariant structural protein patterns provide a substrate for affinity maturation in the membrane-anchored HA regions, as well as the glycan shield on the membrane-distal HA top part. They can also induce high-affinity binding in antiviral CV–N to HA at two sites, and CVN2 binding is achieved at low-affinity binding sites. Full article

Cyanobacteria are photosynthetic prokaryotic organisms which represent a significant source of novel, bioactive, secondary metabolites, and they are also considered an abundant source of bioactive compounds/drugs, such as dolastatin, cryptophycin 1, curacin toyocamycin, phytoalexin, cyanovirin-N and phycocyanin. Some of these compounds have displayed promising results in successful Phase I, II, III and IV clinical trials. Additionally, the cyanobacterial compounds applied to medical research have demonstrated an exciting future with great potential to be developed into new medicines. Most of these compounds have exhibited strong pharmacological activities, including neurotoxicity, cytotoxicity and antiviral activity against HCMV, HSV-1, HHV-6 and HIV-1, so these metabolites could be promising candidates for COVID-19 treatment. Therefore, the effective large-scale production of natural marine products through synthesis is important for resolving the existing issues associated with chemical isolation, including small yields, and may be necessary to better investigate their biological activities. Herein, we highlight the total synthesized and stereochemical determinations of the cyanobacterial bioactive compounds. Furthermore, this review primarily focuses on the biotechnological applications of cyanobacteria, including applications as cosmetics, food supplements, and the nanobiotechnological applications of cyanobacterial bioactive compounds in potential medicinal applications for various human diseases are discussed. Full article

Global processes, such as climate change, frequent and distant travelling and population growth, increase the risk of viral infection spread. Unfortunately, the number of effective and accessible medicines for the prevention and treatment of these infections is limited. Therefore, in recent years, efforts have been intensified to develop new antiviral medicines or vaccines. In this review article, the structure and activity of the most promising antiviral cyanobacterial products are presented. The antiviral cyanometabolites are mainly active against the human immunodeficiency virus (HIV) and other enveloped viruses such as herpes simplex virus (HSV), Ebola or the influenza viruses. The majority of the metabolites are classified as lectins, monomeric or dimeric proteins with unique amino acid sequences. They all show activity at the nanomolar range but differ in carbohydrate specificity and recognize a different epitope on high mannose oligosaccharides. The cyanobacterial lectins include cyanovirin-N (CV-N), scytovirin (SVN), microvirin (MVN), Microcystisviridis lectin (MVL), and Oscillatoria agardhii agglutinin (OAA). Cyanobacterial polysaccharides, peptides, and other metabolites also have potential to be used as antiviral drugs. The sulfated polysaccharide, calcium spirulan (CA-SP), inhibited infection by enveloped viruses, stimulated the immune system’s response, and showed antitumor activity. Microginins, the linear peptides, inhibit angiotensin-converting enzyme (ACE), therefore, their use in the treatment of COVID-19 patients with injury of the ACE2 expressing organs is considered. In addition, many cyanobacterial extracts were revealed to have antiviral activities, but the active agents have not been identified. This fact provides a good basis for further studies on the therapeutic potential of these microorganisms. Full article

We present a graphene-based biosensor selective to recombinant cyanovirin-N (rCV-N), an antiviral protein that has proven to be an effective microbicide to inhibit HIV replication. We modified the graphene monolayer devices with 1-pyrenebutanoic acid succinimidyl ester, which interacts with both graphene and the primary and secondary amines of antibodies. By monitoring the change in the electrical resistance of the device, we were able to detect rCV-N in solutions in the range of 0.01 to 10 ng/mL, and found that the detection limit was 0.45 pg/mL, which is much smaller than that obtained with currently available techniques. This is important for applications of this microbicide against HIV, since it may be produced at a large scale from soya bean seeds processed using the available industrial processing technologies. The sensor showed high sensitivity, selectivity, and reproducibility. Full article

Cyanobacteria of the genus Nostoc are widespread in all kinds of habitats. They occur in a free-living state or in association with other organisms. Members of this genus belong to prolific producers of bioactive metabolites, some of which have been recognized as potential therapeutic agents. Of these, peptides and peptide-like structures show the most promising properties and are of a particular interest for both research laboratories and pharmaceutical companies. Nostoc is a sole source of some lead compounds such as cytotoxic cryptophycins, antiviral cyanovirin-N, or the antitoxic nostocyclopeptides. Nostoc also produces the same bioactive peptides as other cyanobacterial genera, but they frequently have some unique modifications in the structure. This includes hepatotoxic microcystins and potent proteases inhibitors such as cyanopeptolins, anabaenopeptins, and microginins. In this review, we described the most studied peptides produced by Nostoc, focusing especially on the structure, the activity, and a potential application of the compounds. Full article

Cyanovirin-N (CV-N) is an antiviral lectin with potent activity against enveloped viruses, including HIV. The mechanism of action involves high affinity binding to mannose-rich glycans that decorate the surface of enveloped viruses. In the case of HIV, antiviral activity of CV-N is postulated to require multivalent interactions with envelope protein gp120, achieved through a pseudo-repeat of sequence that adopts two near-identical glycan-binding sites, and possibly involves a 3D-domain-swapped dimeric form of CV-N. Here, we present a covalent dimer of CV-N that increases the number of active glycan-binding sites, and we characterize its ability to recognize four glycans in solution. A CV-N variant was designed in which two native repeats were separated by the “nested” covalent insertion of two additional repeats of CV-N, resulting in four possible glycan-binding sites. The resulting Nested CV-N folds into a wild-type-like structure as assessed by circular dichroism and NMR spectroscopy, and displays high thermal stability with a T_m of 59 °C, identical to WT. All four glycan-binding domains encompassed by the sequence are functional as demonstrated by isothermal titration calorimetry, which revealed two sets of binding events to dimannose with dissociation constants K_d of 25 μM and 900 μM, assigned to domains B and B’ and domains A and A’ respectively. Nested CV-N displays a slight increase in activity when compared to WT CV-N in both an anti-HIV cellular assay and a fusion assay. This construct conserves the original binding specifityies of domain A and B, thus indicating correct fold of the two CV-N repeats. Thus, rational design can be used to increase multivalency in antiviral lectins in a controlled manner. Full article

Lectins including flowering plant lectins, algal lectins, cyanobacterial lectins, actinomycete lectin, worm lectins, and the nonpeptidic lectin mimics pradimicins and benanomicins, exhibit anti-HIV activity. The anti-HIV plant lectins include Artocarpus heterophyllus (jacalin) lectin, concanavalin A, Galanthus nivalis (snowdrop) agglutinin-related lectins, Musa acuminata (banana) lectin, Myrianthus holstii lectin, Narcissus pseudonarcissus lectin, and Urtica diocia agglutinin. The anti-HIV algal lectins comprise Boodlea coacta lectin, Griffithsin, Oscillatoria agardhii agglutinin. The anti-HIV cyanobacterial lectins are cyanovirin-N, scytovirin, Microcystis viridis lectin, and microvirin. Actinohivin is an anti-HIV actinomycete lectin. The anti-HIV worm lectins include Chaetopterus variopedatus polychaete marine worm lectin, Serpula vermicularis sea worm lectin, and C-type lectin Mermaid from nematode (Laxus oneistus). The anti-HIV nonpeptidic lectin mimics comprise pradimicins and benanomicins. Their anti-HIV mechanisms are discussed. Full article

CVN (cyanovirin-N) is an anti-HIV protein. CVNH (cyanovirin-N homology) represents its homology. In a previous study, we first reported the full-length sequences of the CVNH gene cloned from Ceratopteris thalictroides. Based on the finding, the coding sequence of CtCVNH was optimized in the study, and then a pET prokaryotic expression vector was constructed. The purification and identification of CtCVNH protein were investigated, as well. SDS-PAGE analysis indicated that a 31 kDa protein was overexpressed and mainly accumulated in the soluble fraction. Only a single protein was obtained after the Ni- nitrilotriacetic acid (NTA) affinity chromatography. The purified protein was identified to be the recombinant CtCVNH by both Western blot and peptide mass fingerprinting analysis. Full article

The development and use of topical microbicides potentially offers an additional strategy to reduce the spread of the Human Immunodeficiency Virus (HIV). Carbohydrate-binding agents (CBAs) that show specificity for high mannose carbohydrates on the surface of the heavily glycosylated envelope of HIV are endowed with potent anti-HIV activity. In fact, a number of algal lectins such as cyanovirin-N, microvirin, microcystis viridis lectin, scytovirin, Oscillatoria agardhii agglutinin and griffithsin are considered as potential microbicide candidates to prevent the sexual transmission of HIV through topical applications. They not only inhibit infection of cells by cell-free virus but they can also efficiently prevent virus transmission from virus-infected cells to uninfected CD4⁺ target T-lymphocytes and DC-SIGN-directed capture of HIV-1 and transmission to CD4⁺ T lymphocytes. This review focuses on the structural properties and carbohydrate specificity of these algal lectins, their antiviral activity against HIV and several other enveloped viruses, their safety profile and viral resistance patterns. Full article