Molecular characterization, receptor binding property, and replication in chickens and mice of H9N2 avian influenza viruses isolated from chickens, peafowls, and wild birds in eastern China

H9N2 avian influenza viruses are widely prevalent in birds and pose an increasing threat to humans because of their enhanced virulence and transmissibility in mammals. Active surveillance on the prevalence and evolution of H9N2 viruses in different avian hosts will help develop eradication measures. We isolated 16 H9N2 viruses from chickens, green peafowls, and wild birds in eastern China from 2017 to 2019 and characterized their comparative genetic evolution, receptor-binding specificity, antigenic diversity, replication, and transmission in chickens and mice. The phylogenetic analysis indicated that the green peafowl viruses and swan reassortant shared the same ancestor with the poultry H9N2 viruses prevalent in eastern China, while the seven wild bird viruses belonged to wild bird lineage. The chicken, peafowl, and swan H9N2 viruses that belonged to the poultry lineage preferentially recognized α-2, 6-linked sialic acids (human-like receptor), but the wild bird lineage viruses can bind both α-2, 3 (avian-like receptor) and human-like receptor similarly. Interestingly, the H9N2 viruses of poultry lineage replicated well and transmitted efficiently, but the viruses of wild bird lineage replicated and transmitted with low efficiency. Importantly, the H9N2 viruses of poultry lineage replicated in higher titer in mammal cells and mice than the viruses of wild birds lineage. Altogether, our study indicates that co-circulation of the H9N2 viruses in poultry, wild birds, and ornamental birds increased their cross-transmission risk in different birds because of their widespread dissemination.

Functional design of glycan-conjugated molecules using a chemoenzymatic approach

Carbohydrates play important and diverse roles in the fundamental processes of life. We have established a method for accurately and a large-scale synthesis of functional carbohydrates with diverse properties using a unique enzymatic method. Furthermore, various artificial glycan-conjugated molecules have been developed by adding these synthetic carbohydrates to macromolecules and to middle- and low-molecular-weight molecules with different properties. These glycan-conjugated molecules have biological activities comparable to or higher than those of natural compounds and present unique functions. In this review, several synthetic glycan-conjugated molecules are taken as examples to show design, synthesis, and function.

Agglutination of Human Polyomaviruses by Using a Tetravalent Glycocluster as a Cross-Linker

Two kinds of tetravalent double-headed sialo-glycosides with short/long spacers between the Neu5Acα2,6Galβ1,4GlcNAc unit and ethylene glycol tetraacetic acid (EGTA) scaffold were found to be capable of binding to virus-like particles of Merkel cell polyomavirus (MCPyV-LP). The binding process and time course of interaction between the tetravalent ligand and MCPyV-LP were assessed by dynamic light scattering (DLS). On the addition of increasing concentrations of ligand to MCPyV-LP, larger cross-linked aggregates formed until a maximum size was reached. The binding was stronger for the tetravalent ligand with a short spacer than for that with a long spacer. The binding of the former ligand to the virus was observed to proceed in two stages during agglutination. The first step was the spontaneous formation of small aggregates comprising the cross-linked ligand-virus complex. In the second step, the aggregates grew successively larger by cooperative binding among the initially produced small aggregates. In transmission electron microscopy, the resulting complex was observed to form aggregates in which the ligands were closely packed with the virus particles. The cross-linked interaction was further confirmed by a simple membrane filtration assay in which the virus-like particles were retained on the membrane when complexed with a ligand. The assay also showed the effective capture of particles of pathogenic, infectious human polyomavirus JCPyV when complexed with a ligand, suggesting its possible application as a method for trapping viruses by filtration under conditions of virus aggregation. Collectively, these results show that the tetravalent glycocluster serves as a ligand not only for agglutinating MCPyV-LP but also for trapping the pathogenic virus.

Hemagglutinin Inhibitors are Potential Future Anti-Influenza Drugs for Mono- and Combination Therapies

Infections by H1-H16 influenza A viruses require sufficient binding of viral hemagglutinins (HAs) to specific target receptors, glycoconjugates bearing sialyl sugar chains, on the host cell surface. Synthesized sialyl sugar chains targeting sialyl sugar-binding sites in HAs that are immutable as long as the virus does not switch to a different host species might therefore be highly effective candidate drugs for inhibition of the initial required step of virus entry. In this chapter, we describe the following aspects of updated sialyl sugar chains as influenza A virus HA inhibitors (HAIs): (1) mode of terminal sialyl-galactose linkage, (2) molecular length and structure of sialyl glycan receptors, (3) multivalent sialyl sugar chain dimension, (4) clustering of sialyl sugar chains on macromolecular scaffolds, and (5) enhancement of the stability of sialyl sugar chain HA inhibitors. We also discuss about the use of HAI-based combinations that should be considered for future influenza therapy.

Divalent Sialylated Precision Glycooligomers Binding to Polyomaviruses and the Effect of Different Linkers

Divalent precision glycooligomers terminating in N-acetylneuraminic acid (Neu5Ac) or 3'-sialyllactose (3'-SL) with varying linkers between scaffold and the glycan portions are synthesized via solid phase synthesis for co-crystallization studies with the sialic acid-binding major capsid protein VP1 of human Trichodysplasia spinulosa-associated Polyomavirus. High-resolution crystal structures of complexes demonstrate that the compounds bind to VP1 depending on the favorable combination of carbohydrate ligand and linker. It is found that artificial linkers can replace portions of natural carbohydrate linkers as long as they meet certain requirements such as size or flexibility to optimize contact area between ligand and receptor binding sites. The obtained results will influence the design of future high affinity ligands based on the structures presented here, and they can serve as a blueprint to develop multivalent glycooligomers as inhibitors of viral adhesion.

Enzymatic Cascade Synthesis Provides Novel Linear Human Milk Oligosaccharides as Reference Standards for xCGE-LIF Based High-Throughput Analysis

A rising amount of known health benefits leads to an increased attention of science and nutrient industry to human milk oligosaccharides (HMOS). The unique diversity of HMOS includes several rare, complex, and high molecular weight structures. Therefore, identification and elucidation of complex structures, which may occur only in traces, poses a daunting analytical challenge, further complicated by the limited access to suitable standards. Regarding this, inherent diversity of HMOS and their structural complexity make them difficult to synthesize. The use of recombinant Leloir-glycosyltransferases offers a common strategy to overcome the latter issues. In this study, linear long-chained Lacto-N-biose-type (LNT) and Lacto-N-neo-type (LNnT) HMOS are tailored far beyond the known naturally occurring length. Thereby novel well-defined reference standards for screening HMOS composition by high performance and high throughput analytics are provided. It is shown here for the first time the synthesis of LNT oligomers up to 26 and LNnT oligomers up to 30 sugar units in a semi-sequential one-pot synthesis as analyzed by high performance multiplexed capillary gel electrophoresis with laser-induced fluorescence detection (xCGE-LIF). While being a high-throughput method, xCGE-LIF can also handle long chained linkage isomers of challenging similarity, some of them even present only in trace amounts.

Characterization of H5N1 Influenza Virus Quasispecies with Adaptive Hemagglutinin Mutations from Single-Virus Infections of Human Airway Cells

Transmission of avian influenza (AI) viruses to mammals involves phylogenetic bottlenecks that select small numbers of variants for transmission to new host species. However, little is known about the AI virus quasispecies diversity that produces variants for virus adaptation to humans. Here, we analyzed the hemagglutinin (HA) genetic diversity produced during AI H5N1 single-virus infection of primary human airway cells and characterized the phenotypes of these variants. During single-virus infection, HA variants emerged with increased fitness to infect human cells. These variants generally had decreased HA thermostability, an indicator of decreased transmissibility, that appeared to compensate for their increase in α2,6-linked sialic acid (α2,6 Sia) binding specificity and/or in the membrane fusion pH threshold, each of which is an advantageous mutational change for viral infection of human airway epithelia. An HA variant with increased HA thermostability also emerged but could not outcompete variants with less HA thermostability. These results provided data on HA quasispecies diversity in human airway cells.IMPORTANCE The diversity of the influenza virus quasispecies that emerges from a single infection is the starting point for viral adaptation to new hosts. A few studies have investigated AI virus quasispecies diversity during human adaptation using clinical samples. However, those studies could be appreciably affected by individual variability and multifactorial respiratory factors, which complicate identification of quasispecies diversity produced by selective pressure for increased adaptation to infect human airway cells. Here, we found that detectable HA genetic diversity was produced by H5N1 single-virus infection of human airway cells. Most of the HA variants had increased fitness to infect human airway cells but incurred a fitness cost of less HA stability. To our knowledge, this is the first report to characterize the adaptive changes of AI virus quasispecies produced by infection of human airway cells. These results provide a better perspective on AI virus adaptation to infect humans.

Human Milk Oligosaccharides as Promising Antivirals

Human milk oligosaccharides (HMOs) are diverse unconjugated carbohydrates that are highly abundant in human breast milk. These glycans are investigated in the context of exhibiting multiple functions in infant growth and development. They seem to provide protection against infectious diseases, including a number of poorly manageable viral infections. Although the potential mechanism of the HMO antiviral protection is rather broad, much of the current experimental work has focused on studying of HMO antiadhesive properties. HMOs may mimic structures of viral receptors and block adherence to target cells, thus preventing infection. Still, the potential of HMOs as a source for new antiviral drugs is relatively unexploited. This can be partly attributed to the extreme complexity of the virus-carbohydrate interactions and technical difficulties in HMO isolation, characterization, and manufacturing procedures. Fortunately, we are currently entering a period of major technological advances that have enabled deeper insights into carbohydrate mediated viral entry, rational selection of HMOs as anti-entry inhibitors, and even evaluation of individual synthetic HMO structures. Here, we provide an up-to-date review on glycan binding studies for rotaviruses, noroviruses, influenza viruses, and human immunodeficiency viruses. We also discuss the preventive and therapeutic potential of HMOs as anti-entry inhibitors and address challenges on the route from fundamental studies to clinical trials.

Chemoenzymatic synthesis and characterization of N-glycolylneuraminic acid-carrying sialoglycopolypeptides as effective inhibitors against equine influenza virus hemagglutination

A series of novel sialoglycopolypeptides carrying N-glycolylneuraminic acid (Neu5Gc)-containing trisaccharides having α(2 → 3)- and α(2 → 6)-linkages in the side chains of γ-polyglutamic acid (γ-PGA) were designed as competitive inhibitors against equine influenza viruses (EIV), which critically recognize the Neu5Gc residue for receptor binding. Using horse red blood cells (HRBC) we successfully evaluated the binding activity of the multivalent Neu5Gc ligands to both equine and canine influenza viruses in the hemagglutination inhibition (HI) assay. Our findings show the multivalent α2,3-linked Neu5Gc-ligands (3a-c and 7) selectively inhibit hemagglutination mediated by both influenza viruses and display a strong inhibitory activity. Our results indicate that the multivalent Neu5Gc-ligands can be used as novel probes to elucidate the mechanism of infection/adhesion of Neu5Gc-binding influenza viruses.

Multivalent Peptide-Nanoparticle Conjugates for Influenza-Virus Inhibition

To inhibit binding of the influenza A virus to the host cell glycocalyx, we generate multivalent peptide-polymer nanoparticles binding with nanomolar affinity to the virus via its spike protein hemagglutinin. The chosen dendritic polyglycerol scaffolds are highly biocompatible and well suited for a multivalent presentation. We could demonstrate in vitro that by increasing the size of the polymer scaffold and adjusting the peptide density, viral infection is drastically reduced. Such a peptide-polymer conjugate qualified also in an in vivo infection scenario. With this study we introduce the first non-carbohydrate-based, covalently linked, multivalent virus inhibitor in the nano- to picomolar range by ensuring low peptide-ligand density on a larger dendritic scaffold.

Glycomaterials for probing host-pathogen interactions and the immune response

The initial engagement of host cells by pathogens is often mediated by glycan structures presented on the cell surface. Various components of the glycocalyx can be targeted by pathogens for adhesion to facilitate infection. Glycans also play integral roles in the modulation of the host immune response to infection. Therefore, understanding the parameters that define glycan interactions with both pathogens and the various components of the host immune system can aid in the development of strategies to prevent, interrupt, or manage infection. Glycomaterials provide a unique and powerful tool with which to interrogate the compositional and functional complexity of the glycocalyx. The objective of this review is to highlight some key contributions from this area of research in deciphering the mechanisms of pathogenesis and the associated host response.

Functional analysis of glyco-molecules that bind with influenza virus

Influenza A virus (IAV) recognizes terminal sialic acid of sialoglyco-conjugates on host cells through the viral envelope glycoprotein hemagglutinin (HA), followed by initiation of entry into the cells. Molecular species of sialic acid are largely divided into two moieties: N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc). A receptor for IAV infection generally means Neu5Ac. Almost all equine IAVs and some human, swine, and duck IAVs bind not only to Neu5Ac but also to Neu5Gc. In nonhuman animals, Neu5Gc has been detected in swine and equine tracheas and the duck colon, which are the main replication sites of mammalian and avian IAVs. Therefore, Neu5Gc in these sites has been suggested to be a functional receptor for IAV infection. Humans cannot synthesize Neu5Gc due to a genetic defect of the Neu5Gc-synthesizing enzyme. We evaluated the receptor function of Neu5Gc in IAV infection in human cells. Our results indicated that Neu5Gc expression on the surface of human cells is not a functional receptor for IAV infection and that it has a negative effect on infectivity of IAV possessing Neu5Gc binding ability. IAV also binds to non-sialo 3-O-sulfated galactosylceramide (sulfatide). Sulfatide has been suggested to be a functional receptor for IAV infection. However, we have shown that sulfatide is not a functional receptor for IAV infection and that the binding of HA with sulfatide enhances progeny virus production. It is expected that functions of these glyco-molecules can be used in prevention and development of new drugs against IAV.

Binding of Galectin-3, a β-Galactoside-binding Lectin, to MUC1 Protein Enhances Phosphorylation of Extracellular Signal-regulated Kinase 1/2 (ERK1/2) and Akt, Promoting Tumor Cell Malignancy

Both mucin 1 (MUC1) and galectin-3 are known to be overexpressed in various malignant tumors and associated with a poor prognosis. It has been extensively reported that MUC1 is involved in potentiation of growth factor-dependent signal transduction. Because some carbohydrate moieties carried on MUC1 change to preferable ones for binding of galectin-3 in cancer cells, we speculated that MUC1-mediated signaling may occur through direct binding of galectin-3. Immunochemical studies showed that the distribution of galectin-3 coincided with that of MUC1 in various human tumor tissues but not in human nonmalignant tissues, and the level of galectin-3 retained on the surface of various cancer cells paralleled that of MUC1. Treatment of MUC1-expressing cells with galectin-3 induced phosphorylation of ERK1/2 and Akt following enhanced phosphorylation of MUC1 C-terminal domain, consistently promoting tumor cell malignancy. It is also noted that this enhanced phosphorylation occurred independently of EGF receptor-mediated signaling in both EGF receptor- and MUC1-expressing cells, and multivalency of galectin-3 was important for initiation of MUC1-mediated signaling. Expectedly, both silencing of endogenous galectin-3 and treatment with galectin-3 antagonists down-regulated cell proliferation of MUC1-expressing cells. These results suggest that the binding of galectin-3 to MUC1 plays a key role in MUC1-mediated signaling. Thus, constitutive activation of MUC1-mediated signaling in an autocrine/paracrine manner caused by ligation of galectin-3 promotes uncontrolled tumor cell malignancy. This signaling may be another MUC1-mediated pathway and function in parallel with a growth factor-dependent MUC1-mediated signaling pathway.

Characterization of H5N1 influenza virus variants with hemagglutinin mutations isolated from patients

A change in viral hemagglutinin (HA) receptor binding specificity from α2,3- to α2,6-linked sialic acid is necessary for highly pathogenic avian influenza (AI) virus subtype H5N1 to become pandemic. However, details of the human-adaptive change in the H5N1 virus remain unknown. Our database search of H5N1 clade 2.2.1 viruses circulating in Egypt identified multiple HA mutations that had been selected in infected patients. Using reverse genetics, we found that increases in both human receptor specificity and the HA pH threshold for membrane fusion were necessary to facilitate replication of the virus variants in human airway epithelia. Furthermore, variants with enhanced replication in human cells had decreased HA stability, apparently to compensate for the changes in viral receptor specificity and membrane fusion activity. Our findings showed that H5N1 viruses could rapidly adapt to growth in the human airway microenvironment by altering their HA properties in infected patients and provided new insights into the human-adaptive mechanisms of AI viruses.

Circulation between bird and human hosts may allow H5N1 viruses to acquire amino acid changes that increase fitness for human infections. However, human-adaptive changes in H5N1 viruses have not been adequately investigated. In this study, we found that multiple HA mutations were actually selected in H5N1-infected patients and that H5N1 variants with some of these HA mutations had increased human-type receptor specificity and increased HA membrane fusion activity, both of which are advantageous for viral replication in human airway epithelia. Furthermore, HA mutants selected during viral replication in patients were likely to have less HA stability, apparently as a compensatory mechanism. These results begin to clarify the picture of the H5N1 human-adaptive mechanism.

Bifunctional thiosialosides inhibit influenza virus

We have synthesized a panel of bivalent S-sialoside analogues, with modifications at the 4 position, as inhibitors of influenza virus. These first generation compounds show IC50 values ranging from low micromolar to high nanomolar in enzyme inhibition and plaque reduction assays with two intact viruses, Influenza H1N1 (A/California/07/2009) and H3N2 (A/Hongkong/8/68).

Glycopolymers with secondary binding motifs mimic glycan branching and display bacterial lectin selectivity in addition to affinity

Polymer architecture is exploited as an alternative to glycan synthesis to enhance selectivity towards pathogenic lectins.

Sensitive and direct detection of receptor binding specificity of highly pathogenic avian influenza A virus in clinical samples

Influenza A virus (IAV) recognizes two types of N-acetylneuraminic acid (Neu5Ac) by galactose (Gal) linkages, Neu5Acα2,3Gal and Neu5Acα2,6Gal. Avian IAV preferentially binds to Neu5Acα2,3Gal linkage, while human IAV preferentially binds to Neu5Acα2,6Gal linkage, as a virus receptor. Shift in receptor binding specificity of avian IAV from Neu5Acα2,3Gal linkage to Neu5Acα2,6Gal linkage is generally believed to be a critical factor for its transmission ability among humans. Surveillance of this shift of highly pathogenic H5N1 avian IAV (HPAI) is thought to be a very important for prediction and prevention of a catastrophic pandemic of HPAI among humans. In this study, we demonstrated that receptor binding specificity of IAV bound to sialo-glycoconjugates was sensitively detected by quantifying the HA gene with real-time reverse-transcription-PCR. The new assay enabled direct detection of receptor binding specificity of HPAIs in chicken clinical samples including trachea and cloaca swabs in only less than 4 h.

Design and synthesis of glycoprotein-based multivalent glyco-ligands for influenza hemagglutinin and human galectin-3

We report a facile synthesis of glycoprotein-based glyco-ligands and their binding with influenza hemagglutinin and human galectin-3. Human serum albumin (HSA) was used as the scaffold and an Asn-linked complex type N-glycan prepared from chicken eggs was used as the glycan building block. It was found that Cu(I)-catalyzed alkyne-azide cycloaddition reaction (click chemistry) between the alkyne-labeled glycan and the azide-tagged HSA led to an efficient formation of the glycoconjugates. The density of glycan ligands on the protein scaffold was readily varied by changing the molar ratios of the two reactants. Binding studies indicated that the sialylated and desialylated multivalent glycoligands could selectively bind to influenza hemagglutinin and human galectin-3, respectively, with high affinity. In the two glycan-lectin interactions, a clear multivalent effect was observed. Moreover, a cell-based assay showed that the synthetic multivalent glyco-ligands could efficiently inhibit the attachment of galectin-3 to human prostate cancer and lung cancer cell lines. This study suggests that the synthetic glycoprotein-based glyco-ligands can be useful for different applications, including blocking the function of galectin-3 in cancer metastasis.

Design and synthesis of a novel ganglioside ligand for influenza A viruses

A novel ganglioside bearing Neuα2-3Gal and Neuα2-6Gal structures as distal sequences was designed as a ligand for influenza A viruses. The efficient synthesis of the designed ganglioside was accomplished by employing the cassette coupling approach as a key reaction, which was executed between the non-reducing end of the oligosaccharide and the cyclic glucosylceramide moiety. Examination of its binding activity to influenza A viruses revealed that the new ligand is recognized by Neuα2-3 and 2-6 type viruses.

Infectivity and pathogenicity of canine H3N8 influenza A virus in horses

Please cite this paper as: Yamanaka et al. (2010) Infectivity and pathogenicity of canine H3N8 influenza A virus in horses. Influenza and Other Respiratory Viruses 4(6), 345–351.

Background  Equine H3N8 influenza A viruses (EIVs) cause respiratory disease in horses and circulate among horses worldwide. In 2004, an outbreak of canine H3N8 influenza A virus (CIV) occurred among dogs in Florida and has spread among dogs in the United States (US). Genetic analyses revealed that this CIV is closely related to the recent EIVs. Although CIV‐infected dogs could be the source of H3N8 influenza A virus for horses, it remains unclear whether the CIV circulating in the United States still maintains its infectivity and/or pathogenicity in horses. To address this, we investigated the infectivity and pathogenicity of CIV in horses and the receptor binding specificity of CIV.

Materials and methods  Three horses were inoculated with A/canine/Colorado/30604/2006 (CO06, H3N8). Clinical signs and nasal swabs were recorded or collected every day. We also evaluated the virus binding to α2‐3‐linked 5‐N‐acetylneuraminic acid (NeuAcα2‐3Gal) and 5‐N‐glycolylneuraminic acid (NeuGcα2‐3Gal) receptor analogues.

Results  Although all the three horses inoculated with CO06 seroconverted, they showed only mild clinical signs and two of them showed no virus shedding. CO06 had reduced binding to NeuGcα2‐3Gal.

Discussion  Our results demonstrated that CO06 had reduced proliferation ability and pathogenicity in horses. As the recognition of NeuGcα2‐3Gal by EIV is known to be essential for binding to the equine respiratory system, the decreased binding of CO06 to NeuGcα2‐3Gal may be one of the important factors that reduces the proliferation ability and pathogenicity of CO06 in horses.

Grafted glycopolymer-based receptor mimics on polymer support for selective adhesion of bacteria

A sugar-containing monomer (2-lactobionamidoethyl methacrylate, LAMA) was grafted on a polypropylene (PP) microfiltration membrane surface by UV-induced graft copolymerization. The degree of grafting can be controlled by variation of monomer concentration, UV irradiation time, and photoinitiator concentration. Fourier transform infrared spectroscopy and scanning electron microscopy were employed to confirm the surface modification on the membranes. The water contact angle was used to evaluate the hydrophilicity change of the membrane surface before and after modification. Bacteria capture experiments showed that the membrane could selectively bind E. faecalis while adhesion of S. maltophilia was not influenced by the functionalization of PP with grafted poly(LAMA). The adhesion of E. faecalis onto poly(LAMA) grafted membrane could be inhibited by 200 mM galactose solution; however, glucose solution showed no inhibition effect. Moreover, occupying sugar residues on the membrane surface primarily by a galactose targeting lectin, peanut agglutinin, could significantly suppress the following adhesion of E. faecalis. All these results clearly demonstrate that this poly(LAMA) grafted PP membrane can selectively capture E. faecalis and that this selection is based on the interaction between galactose side groups on grafted flexible functional polymer chains on the membrane surface and galactose binding protein on the E. faecalis cell membrane.

Immunomodulation of monocyte-derived dendritic cells through ligation of tumor-produced mucins to Siglec-9

Dendritic cells (DCs) play an essential role in the induction and maintenance of an effective immune response and express multiple siglecs. In the present study, we investigated whether or not the ligation of tumor-produced mucins with Siglec-9 expressed on immature DCs is related to escape from immunosurveillance in the tumor-bearing state. Expression of Siglec-9 was up-regulated on the development of monocytes into immature DCs and was decreased in mature DCs. Binding of various mucins and artificial glycopolymers carrying poly (NeuAc α2,6 LacNAc) or poly (NeuAc α2,3 LacNAc) to Siglec-9 was demonstrated by means of a plate assay. These mucins also bound to the surface of immature DCs. When immature DCs were treated with LPS in the presence of these mucins or artificial glycopolymers, the production of IL-12 was significantly reduced, but that of IL-10 was not. Furthermore, IL-12 production was decreased to a similar level on treatment with anti-Siglec-9 mAb. Mucins prepared from serum of cancer patients actually could bind to Siglec-9. These results suggest that Siglec-9 expressed on DCs is involved in immunoregulation through ligation with mucins in an epithelial cancer patient.

Synthesis of sialyllactosamine clusters using carbosilane as core scaffolds by means of chemical and enzymatic approaches

An efficient synthesis of sialyllactosamine (SiaLacNAc) clusters using carbosilanes as core scaffolds has been accomplished by means of chemical and enzymatic approaches. N-Acetyl-D-glucosamine (GlcNAc) clusters having O-glycosidic linkage or S-glycosidic linkage were chemically synthesized from known intermediates in high yields. The GlcNAc clusters were first used as substrates for beta1,4 galactosyl transferase using UDP-galactose (UDP-Gal) as a sugar source to provide corresponding N-acetyllactosamine clusters. Further sugar elongation of the LacNAc clusters was demonstrated using alpha2,3 sialyl transferase and CMP-neuraminic acid (CMP-NANA) to yield the corresponding SiaLacNAc clusters.

Fabrication of honeycomb-structured porous surfaces decorated with glycopolymers

We prepared breath figure patterns on functional surfaces by the surface segregation of a statistical glycopolymer, (styrene-co-2-(D-glucopyranosyl) aminocarbonyloxy ethyl acrylate (S-HEAGl). The synthesis of the statistical glycopolymer is prepared in a straightforward approach by conventional free radical copolymerization of styrene and the unprotected glycomonomer. Blends of this copolymer and high-molecular-weight polystyrene were spin coated from THF solutions, leading to the formation of surfaces with both controlled functionality and topography. AFM studies revealed that both the composition of the blend and the relative humidity play key roles in the size and distribution of the pores at the interface. Thus, the topographical features obtained on the polymer surfaces during film preparation by the breath figure methodology varied from 200 to 700 nm. Moreover, this approach leads to porous films in which the hydrophilic glycomonomer units are oriented toward the pore interface because upon soft annealing in water the holes are partially swelled. The self-organization of the glycopolymer within the pores was additionally confirmed by the reaction of carbohydrate hydroxyl groups with rhodamine isocyanate. Equally, we demonstrate the bioactivity of the anchored glycopolymers by means of the lectin binding test using concanavalin A (Con A).

Therapeutic targets for influenza – perspectives in drug development

Since new and dangerous influenza virus strains, such as H5N1 “avian flu” and more recently the swine-origin H1N1 “swine flu”, are constantly evolving, the need for effective anti-influenza drugs is pressing. It is becoming clear that the emergence of drug-resistant viruses will be a major potential problem in future efforts to control influenza virus infection. Moreover, development of vaccines against new influenza strains takes several months, and their production capacity is limited. Thus, new classes of anti-influenza drugs are highly sought after. This review focuses mainly on novel strategies, including targeting viral entry into host cells, inhibition of viral transcription and genome replication, and targeting of the NS1 influenza protein. Another approach involves viral RNA silencing by siRNAs or by antisense oligonucleotides. Inhibitors of viral neuraminidase have been the most successful approach in influenza virus breakdown to date. Viral maturation can also be blocked by inhibition of hemagglutinin-processing cellular proteinases. Compounds modifying the host cell immune response have also been reported. Design of specific compounds universally active against all viral variants with a reduced potential for the emergence of drug-resistant mutants is the main challenge in anti-influenza drug development, and the goals in this field are discussed here. A review with 140 references.

Glucosyl hesperidin prevents influenza a virus replication in vitro by inhibition of viral sialidase

Hesperidin, a flavonoid obtained from citrus fruits, is known to have multiple biological activities and antimicrobial activities for human viruses; however, hesperidin has very low solubility in water and the target molecule of hesperidin for influenza virus remains unknown. A water-soluble derivative of hesperidin, glucosyl hesperidin (GH), which was synthesized by regioselective transglycosylation with cyclodextrin glucanotransferase, has been reported to have biological activities that are as or stronger than those of hesperidin. To determine the inhibitory effect of GH on influenza A virus (IAV) infection, Madin-Darby canine kidney (MDCK) cells were treated with GH before, at the same time as, and after IAV inoculation. GH treatment before IAV inoculation had no effect on virus replication, whereas, treatment with GH at the same time as or after IAV inoculation induced distinct reduction in IAV replication. Inhibition analysis of GH against two surface glycoprotein spikes of IAV revealed that GH prevents IAV replication by inhibition of viral sialidase activity that is involved in the entry and release stages on IAV infection but not by receptor binding inhibition. GH had no cytotoxic effects on MDCK cells in a dose range of 0-25 mM. Our results provide useful information for the development of novel sialidase inhibitors for influenza prevention.

An alpha2,6-sialyltransferase cloned from Photobacterium leiognathi strain JT-SHIZ-119 shows both sialyltransferase and neuraminidase activity

We cloned, expressed, and characterized a novel beta-galactoside alpha2,6-sialyltransferase from Photobacterium leiognathi strain JT-SHIZ-119. The protein showed 56-96% identity to the marine bacterial alpha2,6-sialyltransferases classified into glycosyltransferase family 80. The sialyltransferase activity of the N-terminal truncated form of the recombinant enzyme was 1477 U/L of Escherichia coli culture. The truncated recombinant enzyme was purified as a single band by sodium dodecyl sulfate polyacrylamide gel electrophoresis through 3 column chromatography steps. The enzyme had distinct activity compared with known marine bacterial alpha2,6-sialyltransferases. Although alpha2,6-sialyltransferases cloned from marine bacteria, such as Photobacterium damselae strain JT0160, P. leiognathi strain JT-SHIZ-145, and Photobacterium sp. strain JT-ISH-224, show only alpha2,6-sialyltransferase activity, the recombinant enzyme cloned from P. leiognathi strain JT-SHIZ-119 showed both alpha2,6-sialyltransferase and alpha2,6-linkage-specific neuraminidase activity. Our results provide important information toward a comprehensive understanding of the bacterial sialyltransferases belonging to the group 80 glycosyltransferase family in the CAZy database.

Molecular design of spacer-N-linked sialoglycopolypeptide as polymeric inhibitors against influenza virus infection

A series of spacer-N-linked glycopolymers carrying long/short α2,3/6 sialylated glycan were designed as polymeric inhibitors of influenza virus. Lactose (Lac) and N-acetyllactosamine (LN: Galβ1,4GlcNAc) were first converted to spacer-N-linked disaccharide glycosides, followed by consecutive enzymatic addition of GlcNAc and Gal residues to the glycosides. The resulting spacer-N-linked glycosides with di-, tetra-, and hexasaccharides carrying a Lac, LN, lacto-N-neotetraose (LNnT: Galβ1,4GlcNAcβ1,3Galβ1,4Glc), and LNβ1,3LNnT were coupled to the carboxy group of γ-polyglutamic acid (γ-PGA) and enzymatically converted to glycopolypeptides carrying α2,3/6 sialylated glycans. The interactions of a series of sialoglycopolypeptides with avian and human influenza virus strains were investigated using a hemagglutination inhibition assay. The avian virus A/Duck/HongKong/313/4/78 (H5N3) bound specifically, regardless of the structure of the asialo portion. In contrast, human virus A/Aichi/2/68 (H3N2) bound preferentially to long α2,6sialylated glycans with penta- or heptasaccharides in a glycan length-dependent manner. Furthermore, the Sambucus sieboldiana (SNA) lectin was also useful as a model of human virus hemagglutinin (HA) for understanding the carbohydrate binding properties, because the recognition motifs of the inner sugar in the receptor were very similar.

Synthesis of sialoglycopolypeptide for potentially blocking influenza virus infection using a rat alpha2,6-sialyltransferase expressed in BmNPV bacmid-injected silkworm larvae

Background

Sialic acid is a deoxy uronic acid with a skeleton of nine carbons which is mostly found on cell surface in animals. This sialic acid on cell surface performs various biological functions by acting as a receptor for microorganisms, viruses, toxins, and hormones; by masking receptors; and by regulating the immune system. In order to synthesize an artificial sialoglycoprotein, we developed a large-scale production of rat α2,6-sialyltransferase (ST6Gal1). The ST6Gal1 was expressed in fifth instar silkworm larval hemolymph using recombinant both cysteine protease- and chitinase-deficient Bombyx mori nucleopolyhedrovirus (BmNPV-CP^--Chi^-) bacmid. The expressed ST6Gal1 was purified, characterized and used for sialylation of asialoglycopolypeptide. We tested the inhibitory effect of the synthesized α2,6-sialoglycopolypeptide on hemagglutination by Sambucus nigra (SNA) lectin.

Results

FLAG-tagged recombinant ST6Gal1 was expressed efficiently and purified by precipitation with ammonium sulphate followed by affinity chromatography on an anti-FLAG M2 column, generating 2.2 mg purified fusion protein from only 11 silkworm larvae, with a recovery yield of 64%. The purified ST6Gal1 was characterized and its N-glycan patterns were found to be approximately paucimannosidic type by HPLC mapping method. Fluorescently-labelled N-acetyllactosamine (LacNAc) glycoside containing dansyl group was synthesized chemo-enzymatically as high-sensitivity acceptor substrate for ST6Gal1. The acceptor substrate specificity of the enzyme was similar to that of rat liver ST6Gal1. The fluorescent glycoside is useful as a substrate for a highly sensitive picomole assay of ST6Gal1. Asialoglycopolypeptide was regioselectively and quantitatively sialylated by catalytic reaction at the terminal Gal residue to obtain α2,6-sialoglycopolypeptide using ST6Gal1. The α2,6-sialoglycopolypeptide selectively inhibited hemagglutination induced by Sambucus nigra (SNA) lectin, showing about 780-fold higher affinity than the control fetuin. Asialoglycopolypeptide and γ-polyglutamic acid did not affect SNA lectin-mediated hemagglutination.

Conclusion

The recombinant ST6Gal1 from a silkworm expression system is useful for the sialylation of asialoglycopeptide. The sialylated glycoprotein is a valuable tool for investigating the molecular mechanisms of biological and physiological events, such as cell-cell recognition and viral entry during infection.

Bacterial CMP-sialic acid synthetases: production, properties, and applications

Sialic acids are abundant nine-carbon sugars expressed terminally on glycoconjugates of eukaryotic cells and are crucial for a variety of cell biological functions such as cell-cell adhesion, intracellular signaling, and in regulation of glycoproteins stability. In bacteria, N-acetylneuraminic acid (Neu5Ac) polymers are important virulence factors. Cytidine 5'-monophosphate (CMP)-N-acetylneuraminic acid synthetase (CSS; EC 2.7.7.43), the key enzyme that synthesizes CMP-N-acetylneuraminic acid, the donor molecule for numerous sialyltransferase reactions, is present in both prokaryotes and eukaryotic systems. Herein, we emphasize the source, function, and biotechnological applications of CSS enzymes from bacterial sources. To date, only a few CSS from pathogenic bacterial species such as Neisseria meningitidis, Escherichia coli, group B streptococci, Haemophilus ducreyi, and Pasteurella hemolytica and an enzyme from nonpathogenic bacterium, Clostridium thermocellum, have been described. Overall, the enzymes from both Gram-positive and Gram-negative bacteria share common catalytic properties such as their dependency on divalent cation, temperature and pH profiles, and catalytic mechanisms. The enzymes, however, can be categorized as smaller and larger enzymes depending on their molecular weight. The larger enzymes in some cases are bifunctional; they have exhibited acetylhydrolase activity in addition to their sugar nucleotidyltransferase activity. The CSSs are important enzymes for the chemoenzymatic synthesis of various sialooligosaccharides of significance in biotechnology.