Design of a Sialylglycopolymer with a Chitosan Backbone Having Efficient Inhibitory Activity against Influenza Virus Infection

Preventive and therapeutic effects of a super-multivalent sialylated filamentous bacteriophage against the influenza virus

The resurgence of influenza viruses as a significant global threat emphasizes the urgent need for innovative antiviral strategies beyond existing treatments. Here, we present the development and evaluation of a novel super-multivalent sialyllactosylated filamentous phage, termed t-6SLPhage, as a potent entry blocker for influenza A viruses. Structural variations in sialyllactosyl ligands, including linkage type, valency, net charge, and spacer length, were systematically explored to identify optimal binding characteristics against target hemagglutinins and influenza viruses. The selected SLPhage equipped with optimal ligands, exhibited exceptional inhibitory potency in in vitro infection inhibition assays. Furthermore, in vivo studies demonstrated its efficacy as both a preventive and therapeutic intervention, even when administered post-exposure at 2 days post-infection, under 4 lethal dose 50% conditions. Remarkably, co-administration with oseltamivir revealed a synergistic effect, suggesting potential combination therapies to enhance efficacy and mitigate resistance. Our findings highlight the efficacy and safety of sialylated filamentous bacteriophages as promising influenza inhibitors. Moreover, the versatility of M13 phages for surface modifications offers avenues for further engineering to enhance therapeutic and preventive performance.

Synthesis of Multivalent Glycoside-Immobilized Carboxymethyl Cellulose Nanohydrogel Particles with Superadsorption Ability for Lectins

Carboxymethyl cellulose (CMC) is a water-soluble cellulose derivative that is nontoxic, biocompatible, biodegradable, and nonallergenic. As developing an adsorbent material for carbohydrate-binding proteins is challenging, we aimed to synthesize CMC nanohydrogel particles (CMCGPs) with an extremely high lectin adsorption tendency in this study. CMCGPs were used as the backbone of an adsorption carrier that was synthesized by cross-linking CMC with ethylene glycol diglycidyl ether. A series of glycoside-immobilized CMCGPs were synthesized by binding two types of glycans (LacNAc and lactose) to the polyvalent carboxymethyl groups that are present on the CMCGP surface and act as reaction sites. These immobilized glycosides function as molecular recognition sites. Glycan moieties were incorporated into the CMCGP backbone at degrees of immobilization (DI) ranging from 8.7 to 21.0% by altering the reaction composition. LacNAc-CMCGP (3b) showed a 19.9% DI of LacNAc glycoside to the CMCGP carboxymethyl group; on average, its particle size swelled to 418 nm in phosphate-buffered saline, which is approximately 1.4 times its dry-state size. Analyzing the adsorbent properties of glyco-CMCGPs using a lectin-binding assay showed the high structural specificity of glyco-CMCGPs to lectins. The equilibrium isotherm data was explained by the Langmuir adsorption model. Notably, compound 3b adsorbed 1.95 ± 0.05 μg of wheat germ agglutinin (WGA) lectin per 1.0 μg-dry of 3b particles at an adsorption equilibrium time of a few minutes. Furthermore, solid-state 13C nuclear magnetic resonance analysis showed that WGA lectin retained its natural structure without denaturation after binding to LacNAc-CMCGP. These results were also supported by affinity purification experiments of WGA from raw wheat germ extract using LacNAc-CMCGP, demonstrating that glyco-CMCGP is capable of adsorbing and desorbing lectin while maintaining its biological activity. Thus, multivalent glycoside-immobilized CMCGPs that use woody biomass derivatives as the backbone are expected to be applied as biorefinery materials, which specifically and abundantly adsorb not just plant lectins but also pathogenic viruses and toxin proteins.

Chitosan and its derivatives as polymeric anti-viral therapeutics and potential anti-SARS-CoV-2 nanomedicine

The coronavirus pandemic, COVID-19 has a global impact on the lives and livelihoods of people. It is characterized by a widespread infection by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), where infected patients may develop serious medical complications or even face death. Development of therapeutic is essential to reduce the morbidity and mortality of infected patients. Chitosan is a versatile biomaterial in nanomedicine and exhibits anti-microbial, anti-cancer and immunomodulatory properties. This review highlights the progress in chitosan design and application pertaining to the anti-viral effects of chitosan and chitosan derivatives (hydroxypropyl trimethylammonium, sulfate, carboxymethyl, bromine, sialylglycopolymer, peptide and phosphonium conjugates) as a function of molecular weight, degree of deacetylation, type of substituents and their degree and site of substitution. The physicochemical attributes of these polymeric therapeutics are identified against the possibility of processing them into nanomedicine which can confer a higher level of anti-viral efficacy. The designs of chitosan for the purpose of targeting SARS-CoV-2, as well as the ever-evolving strains of viruses with a broad spectrum anti-viral activity to meet pandemic preparedness at the early stages of outbreak are discussed.

Optimization of the conditions for the immobilization of glycopolypeptides on hydrophobic silica particulates and simple purification of lectin using glycopolypeptide-immobilized particulates

Glycopolypeptide-immobilized particulates exhibit high binding selectivities and affinities for several analytes. However, to date, the conditions for the synthesis of glycopolypeptide-immobilized particulates have not been optimized and the application of these particulates as carriers for affinity chromatography has not been reported. Accordingly, herein, as a model compound for determining the optimal conditions for the immobilization of an artificial glycopolymer on hexyl-containing hybrid silica particulates (HSPs), the glycopolypeptide poly [GlcNAcβ1,4GlcNAc-β-NHCO-(CH₂)₅NH-/CH₃(CH₂)₉NH-/γ-PGA] (3) containing multivalent chitobiose moieties and multivalent decyl groups with a γ-polyglutamic acid backbone was synthesized. Immobilization of 3 on HSPs under each condition was evaluated by a lectin-binding assay using wheat germ (Triticum vulgaris) agglutinin (WGA), which is an N-acetylglucosamine-binding lectin. As a result, the optimal immobilization conditions for HSPs at 25 mg/mL were obtained at dimethyl sulfoxide (DMSO) concentration of reaction solvent in the range of 1_(DMSO):9_(water) to 4_(DMSO):6_(water) and a compound 3 concentration in the range of 125 nM-1250 nM. Furthermore, the influence of the alkyl group structure introduced into glycopolypeptide for imparting hydrophobicity to it on the immobilization of glycopolypeptide on HSPs was investigated. As a result of comparing three types, poly [GlcNAcβ1,4GlcNAc-β-NHCO-(CH₂)₅NH-/γ-PGA] (1) with no alkyl group, poly [GlcNAcβ1,4GlcNAc-β-NHCO-(CH₂)₅NH-/CH₃(CH₂)₄NH-/γ-PGA] (2) with a pentyl group, and 3 with a decyl group, 3 showed the best immobilization efficiency on HSPs. Finally, 1 mg 3-immobilized HSPs prepared under the optimum conditions adsorbed approximately 7.5 μg WGA in a structure-specific manner. We also achieved a simple WGA purification from raw wheat germ extract as a practical example using 3-immobilized HSPs. We believe that in the future, these glycopolypeptide-immobilized particulates will be used not only for the purification of plant lectins, but also as specific adsorbents for various lectins-like substances such as in vivo lectins, pathogenic viruses, and toxin proteins.

Antiviral Strategies Using Natural Source-Derived Sulfated Polysaccharides in the Light of the COVID-19 Pandemic and Major Human Pathogenic Viruses

Only a mere fraction of the huge variety of human pathogenic viruses can be targeted by the currently available spectrum of antiviral drugs. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak has highlighted the urgent need for molecules that can be deployed quickly to treat novel, developing or re-emerging viral infections. Sulfated polysaccharides are found on the surfaces of both the susceptible host cells and the majority of human viruses, and thus can play an important role during viral infection. Such polysaccharides widely occurring in natural sources, specifically those converted into sulfated varieties, have already proved to possess a high level and sometimes also broad-spectrum antiviral activity. This antiviral potency can be determined through multifold molecular pathways, which in many cases have low profiles of cytotoxicity. Consequently, several new polysaccharide-derived drugs are currently being investigated in clinical settings. We reviewed the present status of research on sulfated polysaccharide-based antiviral agents, their structural characteristics, structure-activity relationships, and the potential of clinical application. Furthermore, the molecular mechanisms of sulfated polysaccharides involved in viral infection or in antiviral activity, respectively, are discussed, together with a focus on the emerging methodology contributing to polysaccharide-based drug development.

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.

Filamentous anti-influenza agents wrapping around viruses

Owing to the emerging resistance to current anti-influenza therapies, strategies for blocking virus-cell interaction with agents that mimic interactions with host cell receptors are garnering interest. In this context, a multivalent presentation of sialyl groups on various types of scaffold materials such as dendrimers, liposomes, nanoparticles, and natural/synthetic polymers has been investigated for the inhibition of influenza A virus infection. However, the development of versatile antiviral agents based on monodisperse scaffolds capable of precise molecular design remains challenging. Whether an anisotropically extended filamentous nanostructure can serve as an effective scaffold for maximum inhibition of viral cell attachment has not been investigated. In this study, the preparation of a series of sialyllactose-conjugated filamentous bacteriophages (SLPhages), with controlled loading levels, ligand valencies, and two types of sialyllactose (α2,3' and α2,6'), is demonstrated. With optimal ligand loading and valency, SLPhages showed inhibitory activity (in vitro) against influenza A viruses at concentrations of tens of picomolar. This remarkable inhibition is due to the strong interaction between the SLPhage and the virus; this interaction is adequately potent to compensate for the cost of the bending and wrapping of the SLPhage around the influenza virus. Our study may open new avenues for the development of filamentous anti-viral agents, in which virus-wrapping or aggregation is the primary feature responsible for the blocking of cell entry.

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.

Controlled synthesis of glycopolymers with pendant complex-type sialylglycopeptides and their binding affinity with a lectin and an influenza virus

Glycopolymers with pendant complex-type sialylglycopeptides (SGPs) were synthesized by a post-polymerization approach. The resulting glycopolymers strongly interacted with a lectin and an influenza virus.

An α2,3-Linked Sialylglycopolymer as a Multivalent Glycoligand Against Avian and Human Influenza Viruses

A glycopolymer bearing α2,3-linked sialyltrisaccharides was synthesized by living radical polymerization using a glycomonomer prepared by a protecting-group-free process, direct azidation of the free sialyllactose, and subsequent azide-alkyne cycloaddition. The prepared glycopolymer with pendant 3´-sialyllactose moieties strongly interacted with both avian and human influenza viruses analyzed by the hemagglutination inhibition assay and the quartz crystal microbalance method.

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.

Generation of a Mutant Mucor hiemalis Endoglycosidase That Acts on Core-fucosylated N-Glycans

Endo-β-N-acetylglucosaminidase M (Endo-M), an endoglycosidase from the fungus Mucor hiemalis, is a useful tool for chemoenzymatic synthesis of glycoconjugates, including glycoprotein-based therapeutics having a precisely defined glycoform, by virtue of its transglycosylation activity. Although Endo-M has been known to act on various N-glycans, it does not act on core-fucosylated N-glycans, which exist widely in mammalian glycoproteins, thus limiting its application. Therefore, we performed site-directed mutagenesis on Endo-M to isolate mutant enzymes that are able to act on mammalian-type core-α1,6-fucosylated glycans. Among the Endo-M mutant enzymes generated, those in which the tryptophan at position 251 was substituted with alanine or asparagine showed altered substrate specificities. Such mutant enzymes exhibited increased hydrolysis of a synthetic α1,6-fucosylated trimannosyl core structure, whereas their activity on the afucosylated form decreased. In addition, among the Trp-251 mutants, the W251N mutant was most efficient in hydrolyzing the core-fucosylated substrate. W251N mutants could act on the immunoglobulin G-derived core-fucosylated glycopeptides and human lactoferrin glycoproteins. This mutant was also capable of transferring the sialyl glycan from an activated substrate intermediate (sialyl glyco-oxazoline) onto an α1,6-fucosyl-N-acetylglucosaminyl biotin. Furthermore, the W251N mutant gained a glycosynthase-like activity when a N175Q substitution was introduced and it caused accumulation of the transglycosylation products. These findings not only give insights into the substrate recognition mechanism of glycoside hydrolase family 85 enzymes but also widen their scope of application in preparing homogeneous glycoforms of core-fucosylated glycoproteins for the production of potent glycoprotein-based therapeutics.

Synthesis of multivalent sialyllactosamine-carrying glyco-nanoparticles with high affinity to the human influenza virus hemagglutinin

A series of multivalent sialoglyco-conjugated nanoparticles were efficiently synthesized by using highly-branched α-glucuronic acid-linked cyclic dextrins (GlcA-HBCD) as a backbone. The sialoglycoside-moieties, with varying degrees of substitution, could be incorporated onto the preformed nanoparticles. These synthesized particles, which are highly soluble in aqueous solution, were shown to have a spherical nanostructure with a diameter of approximately 15nm. The interactions of the sialoglyco-nanoparticles (Neu5Acα2,6LacNAc-GlcA-HBCDs) with human influenza virus strain A/Beijing/262/95 (H1N1) were investigated using a hemagglutination inhibition assay. The sialoglyco-nanoparticle, in which the number of sialic acid substitution is 30, acted as a powerful inhibitor of virus binding activity. We show that both distance and multiplicity of effective ligand-virus formation play important roles in enhancing viral inhibition. Our results indicate that the GlcA-HBCD backbone can be used as a novel spherical nanocluster material for preparing a variety of glyco-nanoparticles to facilitate molecular recognition.

Synthesis of tetravalent LacNAc-glycoclusters as high-affinity cross-linker against Erythrina cristagalli agglutinin

Four kinds of tetravalent double-headed glycoclusters [(LacNAc)4-DHGs] were designed with linkers of varying lengths consisting of alkanedioic carboxyamido groups (C6, C12, C18 and C24) between two bi-antennary LacNAc-glycosides. These glycoclusters served as high-affinity cross-linking ligands for the LacNAc-binding lectin Erythrina cristagalli agglutinin (ECA). The binding activity and cross-linking between each ligand and ECA were characterized by a hemagglutination inhibition (HI) assay, isothermal titration calorimetry (ITC), a quantitative precipitation assay and dynamic light scattering (DLS). For the precipitation assay and DLS measurement, the synthesized (LacNAc)4-DHGs were found to be capable of binding and precipitating the ECA as multivalent ligands. ITC analysis indicated the binding of (LacNAc)4-DHGs was driven by a favorable enthalpy change. Furthermore, the entropy penalty from binding (LacNAc)4-DHGs clearly decreased in a spacer length-dependent manner. The binding affinities of flexible (LacNAc)4-DHGs (C18 and C24) with long spacers were found to be more favorable than those of the clusters having short spacers (C6 and C12). These results were supported by molecular dynamics simulations with explicit water molecules for the tetravalent glycoclusters with ECA. We concluded that the subtle modification in the epitope-presenting scaffolds exerts the significant effect in the recognition efficiency involved in the LacNAc moieties by ECA.

Protecting-Group-Free Synthesis of Glycopolymers Bearing Sialyloligosaccharide and Their High Binding with the Influenza Virus

Glycopolymers having pendant triazole-linked sialyloligosaccharides were successfully synthesized from free saccharides without any protection of the hydroxy and carboxy groups on the saccharides. The glycomonomers were synthesized by the direct azidation of free saccharides using 2-chloro-1,3-dimethylimidazolinium chloride as a condensing agent followed by copper(I)-catalyzed azide-alkyne cycloaddition. The resultant glycomonomers were copolymerized with acrylamide by a reversible addition-fragmentation chain transfer technique. Each of the glycopolymers were obtained and then immobilized on a gold-coated sensor of quartz crystal microbalance to analyze their binding behavior with the lectin. The glycopolymers strongly bound with the corresponding lectin without nonspecific adsorption in aqueous solution. In addition, the glycopolymer bearing a complex-type sialyl N-linked oligosaccharide was found to strongly bind with both human and avian influenza A viruses. The strong binding, observed using the hemagglutination inhibition assay, was attributed to the glycocluster effect of the glycopolymer and the biantennary structure of the N-linked oligosaccharide.

Characteristics of human infection with avian influenza viruses and development of new antiviral agents

Since 1997, several epizootic avian influenza viruses (AIVs) have been transmitted to humans, causing diseases and even deaths. The recent emergence of severe human infections with AIV (H7N9) in China has raised concerns about efficient interpersonal viral transmission, polygenic traits in viral pathogenicity and the management of newly emerging strains. The symptoms associated with viral infection are different in various AI strains: H5N1 and newly emerged H7N9 induce severe pneumonia and related complications in patients, while some H7 and H9 subtypes cause only conjunctivitis or mild respiratory symptoms. The virulence and tissue tropism of viruses as well as the host responses contribute to the pathogenesis of human AIV infection. Several preventive and therapeutic approaches have been proposed to combat AIV infection, including antiviral drugs such as M2 inhibitors, neuraminidase inhibitors, RNA polymerase inhibitors, attachment inhibitors and signal-transduction inhibitors etc. In this article, we summarize the recent progress in researches on the epidemiology, clinical features, pathogenicity determinants, and available or potential antivirals of AIV.

Recent advances in glycotechnology for glycoconjugate synthesis using microbial endoglycosidases

Biotechnology associated with synthesis of glycopeptides and glycoproteins has recently advanced as glycotechnology. Studies toward glycotechonology include the artificial modification of sugar chains in glycoconjugates to improve their function because the physiological importance of sugar chains in living organisms is well recognized. Methods involving addition of oligosaccharides to peptides and proteins have attracted attention as efficient techniques in glycotechnology, especially those involving the transglycosylation activities of microbial endoglycosidases. The exploration of oligosaccharide oxazolines as donor substrates for the transglycosylation of endoglycosidases has significantly enhanced the efficiency of these processes. Moreover, discovery of novel endoglycosidase mutants with glycosynthase-like activity has made it possible to effectively synthesize large quantities of glycopeptides, as well as homogeneous glycoprotein. The use of mutant enzymes and oligosaccharide oxazolines has led to development of practical applications for the synthesis of bioactive glycopeptides and therapeutic glycoproteins as bio-medicines.

Unique gangliosides synthesized in vitro by sialyltransferases from marine bacteria and their characterization: ganglioside synthesis by bacterial sialyltransferases

On the basis of the results outlined in our previous report, bacterial sialyltransferases (ST) from marine sources were further characterized using glycosphingolipids (GSL), especially ganglio-series GSLs, based on the enzymatic characteristics and kinetic parameters obtained by Line weaver-Burk plots. Among them, GA1 and GA2 were found to be good substrates for these unique STs. Thus, new gangliosides synthesized by α2-3 and α2-6STs were structurally characterized by several analytical procedures. The ganglioside generated by the catalytic activity of α2-3ST was identified as GM1b. On the other hand, when enzyme reactions by α2-6STs were performed using substrates GA2 and GA1, very unique gangliosides were generated. The structures were identified as NeuAcα2-6GalNAcβ1-4Galβ1-4Glcβ-Cer and NeuAcα2-6Galβ1-3GalNAcβ1-4Galβ1-4Glcβ-Cer, respectively. The synthesized ganglioside NeuAcα2-6GalNAcβ1-4Galβ1-4Glcβ-Cer showed binding activity to the influenza A virus {A/Panama/2007/99 (H3N2)} at a similar level to purified sialyl(α2-3)paragloboside (S2-3PG) and sialyl(α2-6)paragloboside (S2-6PG) from mammalian sources. The evidence suggests that these STs have unique features, including substrate specificities restricted not only to lacto-series but also to ganglio-series GSLs, as well as catalytic potentials for ganglioside synthesis. This evidence demonstrates that effective in vitro ganglioside synthesis could be a valuable tool for selectively synthesizing sialic acid (Sia) modifications, thereby preparing large-scale gangliosides and permitting the exploration of unknown functions.

Biological analysis of the microbial metabolism of hetero-oligosaccharides in application to glycotechnology

This review describes the relationship between hetero-oligosaccharides and microorganisms. It is possible to prepare aminosugar nucleotides as donors for hetero-oligosaccharide synthesis with a combination of yeast fermentation and bacterial enzymes, and to use the product to test for a rare human blood group. We have isolated various glycosidases produced by microorganisms, mainly from soil, to elucidate the structure and function of hetero-oligosaccharides. Among them, a mold endoglycosidase was found to have specific transglycosylation activity in addition to hydrolysis activity, and we have used it to synthesize chemo-enzymatically various bioactive glycopeptides by the attachment of a hetero-oligosaccharide to a peptide. We found that lactic acid bacteria bound to a hetero-oligosaccharide on the intestinal tract cell surface in animals. We also analyzed the bifidobacterial hetero-oligosaccharide-hydrolyzing enzymes involved in the degradation of mucin glycoprotein in the host intestinal tract and human milk oligosaccharides, and identified a specific saccharide that acted as a bifidobacteria growth factor.

Capture of influenza viruses and prevention of their infection by coral mineral powder (sango mineral powder)

The anti-influenza virus activity of fossilized marine coral powder (sango mineral powder, SMP) was studied. SMP is composed in terms of mass of around 25 % of calcium and 10 % of magnesium, respectively, principally as dolomite (CaMg(CO(3))(2)) but not as calcium oxide (CaO) or magnesium oxide (MgO). By mixing the influenza virus with SMP, the infectivity of the virus substantially decreased and there was more than a 10(4) reduction on the 3rd d of infection. The antiviral effect was observed against all the type A and B strains of the influenza virus examined including the H1N1 2009 pandemic and H5N1 avian viruses. The surface structure of SMP was highly porous and the anti-influenza activity was explained by the adsorption of the viral particles onto its surface. The binding of viruses to SMP was strong and stable in the physiological condition, and the attached viruses detached only in the presence of a high concentration of phosphate. This was similar to the binding of protein to hydroxyapatite, suggesting an ionic interaction between SMP and the viral proteins. SMP maintained its activity to capture influenza viruses even after being immobilized on a non-woven textile. SMP would be useful as a practical anti-influenza tool especially in preparation for the next pandemic virus.

Synthesis of galabiose-chitosan conjugate as potent inhibitor of Streptococcus suis adhesion

The aim of this work is to construct a safe and effective drug candidate against Streptococcus suis infection. A panel of chitosan-based polymer conjugates with branched galabiose (Galalpha1-4Gal) side chains was synthesized as inhibitors of S. suis adhesion. The synthesis was achieved by using an aldehyde-functionalized galabiose derivative to graft it onto chitosan amino groups. Structural compositions of the conjugates were verified by 1H NMR spectroscopy and CHN elemental analyses. Potent inhibitory activities of the conjugates against S. suis adhesion to human erythrocytes were determined at low nanomolar concentration by HAI assay. An SPR study revealed a high affinity binding (Kd=39.6 nM) of the conjugate with BSI-B4 lectin. By using biocompatible chitosan as the scaffold for presenting S. suis -specific galabiose units, as well as the concise route tailored for the conjugate syntheses, the present study provides a practical way for explorations of new anti- S. suis therapies.

Marine bacterial sialyltransferases

Sialyltransferases transfer N-acetylneuraminic acid (Neu5Ac) from the common donor substrate of these enzymes, cytidine 5′-monophospho-N-acetylneuraminic acid (CMP-Neu5Ac), to acceptor substrates. The enzymatic reaction products including sialyl-glycoproteins, sialyl-glycolipids and sialyl-oligosaccharides are important molecules in various biological and physiological processes, such as cell-cell recognition, cancer metastasis, and virus infection. Thus, sialyltransferases are thought to be important enzymes in the field of glycobiology. To date, many sialyltransferases and the genes encoding them have been obtained from various sources including mammalian, bacterial and viral sources. During the course of our research, we have detected over 20 bacteria that produce sialyltransferases. Many of the bacteria we isolated from marine environments are classified in the genus Photobacterium or the closely related genus Vibrio. The paper reviews the sialyltransferases obtained mainly from marine bacteria.

Efficient glycosynthase mutant derived from Mucor hiemalis endo-beta-N-acetylglucosaminidase capable of transferring oligosaccharide from both sugar oxazoline and natural N-glycan

Endo-M, an endo-beta-N-acetylglucosaminidase from Mucor hiemalis, is a family 85 glycoside hydrolase. This enzyme is unique in that it can transfer en bloc the oligosaccharide of various types of N-glycans onto different acceptors, and thereby it enzymatically generates diverse glycoconjugates. In this study, we performed mutational and kinetic studies focusing on a key catalytic asparagine 175 of Endo-M. We have shown that most of the Asn-175 mutants had significantly diminished hydrolysis activity but acted as glycosynthases capable of using synthetic sugar oxazoline for transglycosylation. Our results confirm the critical role of this asparagine residue in promoting the formation of an oxazolinium ion intermediate in the first step of the substrate-assisted catalysis. Interestingly, the N175Q mutant was found to possess dramatically enhanced glycosynthase-like activity with sugar oxazoline in comparison with N175A and a transglycosidase-like activity with "natural" N-glycan as well. These results also implicated the significance of amide side chain in the asparagine 175 of Endo-M for promoting oxazoline transglycosylation in the second step of the catalysis. The highly efficient syntheses of glycopeptides/glycoproteins by N175Q combined with synthetic sugar oxazolines or natural N-glycan substrates were exemplified. In addition, we also identified several previously unknown residues that seem to play a role in the catalysis of Endo-M.

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.