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 Neu5Acα2,6Galß1,4GlcNAc 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.

A novel analytical procedure for assaying lysozyme activity using an end-blocked chitotetraose derivative as substrate.

An end-modified ß-d-galactosyl chitotetraose derivative [44-O-ß-d-galactosyl-ß-tri-N-acetylchitotriosyl 2-acetamide-2,3-dideoxy-glucopyranose; Gal(GlcN)3D] was designed and synthesized from chitin tetrasaccharide. The derivative was chemically modified by dehydration of the reducing end GlcN and enzymatic addition of a Gal group to the non-reducing end GlcN. Hydrolysis of Gal(GlcN)3D and related compounds using hen egg-white lysozyme was then examined. Gal(GlcN)3D was specifically cleaved to Gal(GlcN)2 and GlcND. Kinetic studies and docking simulations were further conducted to elucidate its mode of binding to lysozyme. These analyses revealed the binding of Gal(GlcN)3D to lysozyme is more favorable than that of (GlcN)4D. We conclude the 4-O-substituted Gal group at the non-reducing end of Gal(GlcN)3D does not prohibit the action of lysozyme, but gives some affinity to the subsite (i.e. equivalent to GlcN). From these results, a new assay method for quantifying lysozyme was established by utilizing the Morgan-Elson reaction based on the generation of product D (2-acetamide-2,3-dideoxy-glucopyranose), which serves as a chromophore, formed from Gal(GlcN)3D by lysozyme through a conjugated reaction involving ß-N-acetylhexosaminidase. The assay system gave a linear dose-response curve in the range of 2-31 µg of lysozyme during a 15 min incubation. This novel assay method for the quantification of lysozyme is highly specific, sensitive, accurate and reproducible.

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.

Novel enzymatic synthesis of spacer-linked P(k) trisaccharide targeting for neutralization of Shiga toxin.

A novel alkyl spacer-conjugated derivative of P(k) trisaccharide (P(k)), one of the active receptors of Shiga toxins (Stxs; Stx1 and Stx2) produced by pathogenic Escherichia coli (STEC), was designed and synthesized by a combination of cellulase-mediated condensation from Trichoderma reesei and α1,4-galactosyltransferase (LgtC) from Neisseria gonorrhoeae. The specific activity of N. gonorrhoeae LgtC was 66U/mg, which was 13-fold higher than that from N. meningitidis expressed in E. coli. 5-trifluoroacetamidopentyl-ß-P(k) (TFAP-P(k)) was synthesized (yield of 86%, based on the amount of TFAP-lactose added) and its binding to Stx1a-B and Stx2a-B was evaluated. The dissociation constants (KDs) of Stx1a-B and Stx2a-B to the spacer-linked P(k), immobilized on a CM5 sensor chip, were 6.8×10(-6) M (kon=4.1×10(1)M(-1)S(-1), koff=2.8×10(-4)S(-1)) and 2.2×10(-5)M (kon=3.9×10(2)M(-1)S(-1), koff=8.6×10(-3)S(-1)), respectively. This result suggests that the monovalent P(k)-derivative, conjugated to a pentylamino group, represents a promising Stx-neutralizing agent. This cellulase-mediated condensation using cellulase and glycosyltransferase is a valuable tool for the synthesis of spacer-linked oligosaccharide.

The structure of the proteinaceous inhibitor PliI from Aeromonas hydrophila in complex with its target lysozyme.

Recent microbiological data have revealed that Gram-negative bacteria are able to protect themselves against the lytic action of host lysozymes by secreting proteinaceous inhibitors. Four distinct classes of such inhibitors have been discovered that specifically act against c-type, g-type and i-type lysozymes. Here, the 1.24 Šresolution crystal structure of the periplasmic i-type lysozyme inhibitor from Aeromonas hydrophila (PliI-Ah) in complex with the i-type lysozyme from Meretrix lusoria is reported. The structure is the first to explain the inhibitory mechanism of the PliI family at the atomic level. A distinct `ridge' formed by three exposed PliI loops inserts into the substrate-binding groove of the lysozyme, resulting in a complementary `key-lock' interface. The interface is principally stabilized by the interactions made by the PliI-Ah residues Ser104 and Tyr107 belonging to the conserved SGxY motif, as well as by the other conserved residues Ser46 and Asp76. The functional importance of these residues is confirmed by inhibition assays with the corresponding point mutants of PliI-Ah. The accumulated structural data on lysozyme-inhibitor complexes from several classes indicate that in all cases an extensive interface of either a single or a double `key-lock' type is formed, resulting in highly efficient inhibition. These data provide a basis for the rational development of a new class of antibacterial drugs.

Interaction of di-N-acetylchitobiosyl moranoline with a family GH19 chitinase from moss, Bryum coronatum.

Tri-N-acetylchitotriosyl moranoline, (GlcNAc)3-M, was previously shown to strongly inhibit lysozyme (Ogata M, Umemoto N, Ohnuma T, Numata T, Suzuki A, Usui T, Fukamizo T. 2013. A novel transition-state analogue for lysozyme, 4-O-ß-tri-Nacetylchitotriosyl moranoline, provided evidence supporting the covalent glycosyl-enzyme intermediate. J Biol Chem. 288:6072-6082). The findings prompted us to examine the interaction of di-N-acetylchitobiosyl moranoline, (GlcNAc)2-M, with a family GH19 chitinase from moss, Bryum coronatum (BcChi19A). Thermal unfolding experiments using BcChi19A and the catalytic acid-deficient mutant (BcChi19A-E61A) revealed that the transition temperature (Tm) was elevated by 4.3 and 5.8°C, respectively, upon the addition of (GlcNAc)2-M, while the chitin dimer, (GlcNAc)2, elevated Tm only by 1.0 and 1.4°C, respectively. By means of isothermal titration calorimetry, binding free energy changes for the interactions of (GlcNAc)3 and (GlcNAc)2-M with BcChi19A-E61A were determined to be -5.2 and -6.6 kcal/mol, respectively, while (GlcNAc)2 was found to interact with BcChi19A-E61A with markedly lower affinity. nuclear magnetic resonance titration experiments using (15)N-labeled BcChi19A and BcChi19A-E61A revealed that both (GlcNAc)2 and (GlcNAc)2-M interact with the region surrounding the catalytic center of the enzyme and that the interaction of (GlcNAc)2-M is markedly stronger than that of (GlcNAc)2 for both enzymes. However, (GlcNAc)2-M was found to moderately inhibit the hydrolytic reaction of chitin oligosaccharides catalyzed by BcChi19A (IC50 = 130-620 µM). A molecular dynamics simulation of BcChi19A in complex with (GlcNAc)2-M revealed that the complex is quite stable and the binding mode does not significantly change during the simulation. The moranoline moiety of (GlcNAc)2-M did not fit into the catalytic cleft (subsite -1) but was rather in contact with subsite +1. This situation may result in the moderate inhibition toward the BcChi19A-catalyzed hydrolysis.

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.

Expression and purification of bioactive hemagglutinin protein of highly pathogenic avian influenza A (H5N1) in silkworm larvae.

The hemagglutinin (HA) of avian influenza viruses plays a very important role in the infection of host cells. In this study, the HA gene of the highly pathogenic avian influenza H5N1 virus was cloned and expressed in silkworm larvae. The expressed recombinant HA (rHA) was purified using fetuin-agarose chromatography and Superdex 200 10/300 GL gel filtration chromatography, and the identity of purified rHA was confirmed by SDS-PAGE and Western blot. Approximately 500 µg of purified rHA was obtained from a total of 30 silkworm larvae, suggesting the high efficiency of the silkworm expression system. The purified rHA bound to a rabbit polyclonal antibody against influenza A virus H5N1 (avian flu) HA, suggesting its antigenicity and potential application in vaccine development. Gel filtration chromatography showed that purified HA was present in the void volume fractions, indicating that rHA may form an oligomer. The rHA bound to poly{Neu5Acα2,3LacNAcß-O[(CH2)5NHCO]2(CH2)5NH-/γ-PGA}, which mimics an avian type receptor, but did not bind to γ-polyglutamic acid or human type receptor mimic, poly{Neu5Acα2,6LacNAcß-O[(CH2)5NHCO]2(CH2)5NH-/γ-PGA}, suggesting that it could be utilized as a blocking agent against infection by highly pathogenic influenza viruses.

A novel transition-state analogue for lysozyme, 4-O-ß-tri-N-acetylchitotriosyl moranoline, provided evidence supporting the covalent glycosyl-enzyme intermediate.

4-O-ß-Di-N-acetylchitobiosyl moranoline (2) and 4-O-ß-tri-N-acetylchitotriosyl moranoline (3) were produced by lysozyme-mediated transglycosylation from the substrates tetra-N-acetylchitotetraose, (GlcNAc)4, and moranoline, and the binding modes of 2 and 3 to hen egg white lysozyme (HEWL) was examined by inhibition kinetics, isothermal titration calorimetry (ITC), and x-ray crystallography. Compounds 2 and 3 specifically bound to HEWL, acting as competitive inhibitors with Ki values of 2.01 × 10(-5) and 1.84 × 10(-6) m, respectively. From ITC analysis, the binding of 3 was found to be driven by favorable enthalpy change (ΔHr°), which is similar to those obtained for 2 and (GlcNAc)4. However, the entropy loss (-TΔSr°) for the binding of 3 was smaller than those of 2 and (GlcNAc)4. Thus the binding of 3 was found to be more favorable than those of the others. Judging from the Kd value of 3 (760 nm), the compound appears to have the highest affinity among the lysozyme inhibitors identified to date. X-ray crystal structure of HEWL in a complex with 3 showed that compound 3 binds to subsites -4 to -1 and the moranoline moiety adopts an undistorted (4)C1 chair conformation almost overlapping with the -1 sugar covalently bound to Asp-52 of HEWL (Vocadlo, Davies, G. J., Laine, R., and Withers, S. G. (2001) Nature 412, 835-838). From these results, we concluded that compound 3 serves as a transition-state analogue for lysozyme providing additional evidence supporting the covalent glycosyl-enzyme intermediate in the catalytic reaction.

Mode of action of a ß-(1→6)-glucanase from Penicillium multicolor.

ß-(1→6)-Glucanase from the culture filtrate of Penicillium multicolor LAM7153 was purified by ammonium sulfate precipitation, followed by cation-exchange and affinity chromatography using gentiotetraose (Gen4) as ligand. The hydrolytic mode of action of the purified protein on ß-(1→6)-glucan (pustulan) was elucidated in real time during the reaction by HPAEC-PAD analysis. Gentiooligosaccharides (DP 2-9, Gen2₋9), methyl ß-gentiooligosides (DP 2-6, Gen2₋6 ß-OMe), and p-nitrophenyl ß-gentiooligosides (DP 2-6, Gen2₋6 ß-pNP) were used as substrates to provide analytical insight into how the cleavage of pustulan (DP¯ 320) is actually achieved by the enzyme. The enzyme was shown to completely hydrolyze pustulan in three steps as follows. In the initial stage, the enzyme quickly cleaved the glucan with a pattern resembling an endo-hydrolase to produce a short-chain glucan (DP¯ 45) as an intermediate. In the midterm stage, the resulting short-chain glucan was further cleaved into two fractions corresponding to DP 15-7 and DP 2-4 with great regularity. In the final stage, the lower oligomers corresponding to DP 3 and DP 4 were very slowly hydrolyzed into glucose and gentiobiose (Gen2). As a result, the hydrolytic cooperation of both an endo-type and saccharifying-type reaction by a single enzyme, which plays a bifunctional role, led to complete hydrolysis of the glucan. Thus, ß-(1→6)-glucanase varies its mode of action depending on the chain length derived from the glucan.

Facile synthesis of 4-O-ß-N-acetylchitooligosyl 2-acetamido-2,3-dideoxydidehydro-gluconolactone based on the transformation of chitooligosaccharide and its suppressive effects against the furylfuramide-induced SOS response.

A facile synthesis method is described for transforming the reducing-end residue of chitooligosaccharides (DP 2-4) into lactone. The desired 4-O-ß-N-acetylchitooligosyl lactones (GN(n)L) were conveniently prepared from chitooligosaccharides by consecutive dehydration and oxidation reactions to afford 4-O-ß-tri-N-acetylchitotriosyl 2-acetamido-2,3-dideoxydidehydro-gluconolactone (GN(3)L), 4-O-ß-di-N-acetylchitobiosyl 2-acetamido-2,3-dideoxydidehydro-gluconolactone (GN(2)L), and 4-O-ß-2-acetamido-2-deoxy-D-glucopyranosyl 2-acetamido-2,3-dideoxydidehydro-gluconolactone (GNL). The resulting lactone derivatives exhibited considerable suppression (42.6-54.3% at a concentration of 400 µM) in umu gene expression of the SOS response in Salmonella typhimurium TA1535/pSK1002 against the mutagen, 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamido (AF-2). Lactonization of the chitooligosaccharides was found to be essential for their suppression of the SOS-inducing activity.

Enzymatic synthesis of cellulose II-like substance via cellulolytic enzyme-mediated transglycosylation in an aqueous medium.

The enzymatic synthesis of cellulose-like substance via a non-biosynthetic pathway has been achieved by transglycosylation in an aqueous system of the corresponding substrate, cellotriose for cellulolytic enzyme endo-acting endoglucanase I (EG I) from Hypocrea jecorina. A significant amount of water-insoluble product precipitated out from the reaction system. MALDI-TOF mass analysis showed that the resulting precipitate had a degree of polymerization (DP) of up to 16 from cellotriose. Solid-state (13)C NMR spectrum of the resulting water-insoluble product revealed that all carbon resonance lines were assigned to two kinds of anhydroglucose residues in the corresponding structure of cellulose II. X-ray diffraction (XRD) measurement as well as (13)C NMR analysis showed that the crystal structure corresponds to cellulose II with a high degree of crystallinity. We propose the multiple oligomers form highly crystalline cellulose II as a result of self-assembly via oligomer-oligomer interaction when they precipitate.

Enzymatic synthesis of an α-chitin-like substance via lysozyme-mediated transglycosylation.

The enzymatic synthesis of an α-chitin-like substance via a non-biosynthetic pathway has been achieved by transglycosylation in an aqueous system of the corresponding substrate, tri-N-acetylchitotriose [(GlcNAc)(3)] for lysozyme. A significant amount of water-insoluble product precipitated out from the reaction system. MALDI-TOFMS analysis showed that the resulting precipitate had a degree of polymerization (DP) of up to 15 from (GlcNAc)(3). Solid-state (13)C NMR analysis revealed that the resulting water-insoluble product is a chitin-like substance consisting of N-acetylglucosamine (GlcNAc) residues joined exclusively in a ß-(1→4)-linked chain with stringent regio-/stereoselection. X-ray diffraction (XRD) measurement as well as (13)C NMR analysis showed that the crystal structure of synthetic product corresponds to α-chitin with a high degree of crystallinity. We propose that the multiple oligomers form an α-chitin-like substance as a result of self-assembly via oligomer-oligomer interaction when they precipitate.

Design and synthesis of high-avidity tetravalent glycoclusters as probes for Sambucus sieboldiana agglutinin and characterization of their binding properties.

We designed and synthesized three tetravalent sialo-glycoclusters that had different separations between the terminal sialic acids and the linking carboxy groups of the ethylene glycol bis(ß-aminoethyl ether)-N,N,N',N'-tetraacetate scaffold to serve as ligands for the sialic acid-binding lectin Sambucus sieboldiana agglutinin (SSA). The interaction between each glycocluster and SSA was characterized by hemagglutination inhibition, quantitative precipitation, and double-diffusion assays. For the precipitation assays, the precipitin curves indicated that the ligands and SSA bound in either a 1:1 or a 1:2 ratio, i.e., stoichiometrically. The strong interactions of these sialo-glycoclusters with SSA could be ascribed to a combination of multivalency and spacer effects. We also assessed the nature of the ligand-SSA complexes by isothermal titration calorimetry and dynamic light scattering. The results of those experiments indicated that formation of intermolecular complexes occurred at less than stoichiometric ratios of ligand to SSA concentrations and that, as the concentrations of the ligands increased, larger cross-linked aggregates formed. Large aggregates that were present concurrently with visible precipitation and with a particle size centered at ~600 to 800 nm were identified by dynamic light scattering.

Mannose-specific lectin from the mushroom Hygrophorus russula.

A lectin was purified from the mushroom Hygrophorus russula by affinity chromatography on a Sephadex G-50 column and BioAssist S cation exchange chromatography and designated H. russula lectin (HRL). The results of sodium dodecyl sulfate-polyaclylamidegel electrophoresis, gel filtration and matrix-assisted laser desorption ionization time-of-flight mass spectrometry of HRL indicated that it was composed of four identical 18.5 kDa subunits with no S-S linkage. Isoelectric focusing of the lectin showed bands near pI 6.40. The complete sequence of 175 amino acid residues was determined by amino acid sequencing of intact or enzyme-digested HRL. The sequence showed homology with Grifola frondosa lectin. The cDNA of HRL was cloned from RNA extracted from the mushroom. The open reading frame of the cDNA consisted of 528 bp encoding 176 amino acids. In hemagglutination inhibition assay, α1-6 mannobiose was the strongest inhibitor and isomaltose, Glcα1-6Glc, was the second strongest one, among mono- and oligosaccharides tested. Frontal affinity chromatography indicated that HRL had the highest affinity for Manα1-6(Manα1-3)Manß1-4GlcNAcß1-4GlcNAc, and non-reducing terminal Manα1-6 was essential for the binding of HRL to carbohydrate chains. The sugar-binding specificity of HRL was also analyzed by using BIAcore. The result from the analysis exhibited positive correlations with that of the hemagglutination inhibition assay. All the results suggested that HRL recognized the α1-6 linkage of mannose and glucose, especially the Manα1-6 bond. HRL showed a mitogenic activity against spleen lymph cells of an F344 rat. Furthermore, an enzyme-linked immunosorbent assay showed strong binding of HRL to human immunodeficiency virus type-1 gp120.

Lactosylamidine-based affinity purification for cellulolytic enzymes EG I and CBH I from Hypocrea jecorina and their properties.

Selective adsorption and separation of ß-glucosidase, endo-acting endo-ß-(1→4)-glucanase I (EG I), and exo-acting cellobiohydrolase I (CBH I) were achieved by affinity chromatography with ß-lactosylamidine as ligand. A crude cellulase preparation from Hypocrea jecorina served as the source of enzyme. When crude cellulase was applied to the lactosylamidine-based affinity column, ß-glucosidase appeared in the unbound fraction. By contrast, EG I and CBH I were retained on the column and then separated from each other by appropriately adjusting the elution conditions. The relative affinities of the enzymes, based on their column elution conditions, were strongly dependent on the ligand. The highly purified EG I and CBH I, obtained by affinity chromatography, were further purified by Mono P and DEAE chromatography, respectively. EG I and CBH I cleave only at the phenolic bond in p-nitrophenyl glycosides with lactose and N-acetyllactosamine (LacNAc). By contrast, both scissile bonds in p-nitrophenyl glycosides with cellobiose were subject to hydrolysis although with important differences in their kinetic parameters.

Molecular design of fluorescent labeled glycosides as acceptor substrates for sialyltransferases.

A series of dansyl-labeled glycosides with di-, tetra-, and hexasaccharides carrying the terminal N-acetyllactosamine (LacNAc) sequence were synthesized as acceptor substrates for α2,6- and α2,3-sialyltransferases. As an alternative design, dansyl-labeled LacNAc glycoside carrying a long-spacer linked glycan was engineered by replacement of the LacNAc or lactose units with an alkyl chain. In addition, we designed a dansyl-labeled bi-antennary LacNAc glycoside as an N-linked oligosaccharide mimetic, such as asialo-α(1)-acid glycoprotein. The kinetic parameters for the transfer reaction of synthesized dansyl-labeled glycosides by sialyltransferases were determined by the fluorescent HPLC method. The catalytic efficiencies (V(max)/K(m)) of acceptor substrates carrying the terminal LacNAc sequence with various length glycans in the array for α2,6- and α2,3-sialyltransferases decreased in a glycan length-dependent manner. Furthermore, of the acceptor substrates tested, dansyl-labeled bi-antennary LacNAc glycoside displayed the most favorable K(m) value for α2,6- and α2,3-sialyltransferases.

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.

Toxic isolectins from the mushroom Boletus venenatus.

Ingestion of the toxic mushroom Boletus venenatus causes a severe gastrointestinal syndrome, such as nausea, repetitive vomiting, diarrhea, and stomachache. A family of isolectins (B. venenatus lectins, BVLs) was isolated as the toxic principles from the mushroom by successive 80% ammonium sulfate-precipitation, Super Q anion-exchange chromatography, and TSK-gel G3000SW gel filtration. Although BVLs showed a single band on SDS-PAGE, they were further divided into eight isolectins (BVL-1 to -8) by BioAssist Q anion-exchange chromatography. All the isolectins showed lectin activity and had very similar molecular weights as detected by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analysis. Among them, BVL-1 and -3 were further characterized with their complete amino acid sequences of 99 amino acids determined and found to be identical to each other. In the hemagglutination inhibition assay, both proteins failed to bind to any mono- or oligo-saccharides tested and showed the same sugar-binding specificity to glycoproteins. Among the glycoproteins examined, asialo-fetuin was the strongest inhibitor. The sugar-binding specificity of each isolectin was also analyzed by using frontal affinity chromatography and surface plasmon resonance analysis, indicating that they recognized N-linked sugar chains, especially Galbeta1-->4GlcNAcbeta1-->4Manbeta1-->4GlcNAcbeta1-->4GlcNAc (Type II) residues in N-linked sugar chains. BVLs ingestion resulted in fatal toxicity in mice upon intraperitoneal administration and caused diarrhea upon oral administration in rats.