The fluorescence of wheat germ agglutinin and of its complexes with saccharides

Preparation of N-Linked-Type GlcNAc Monomers for Glycopolymers and Binding Specificity for Lectin

Glycomonomers having N-glycosidic linkages were prepared from a known glycosyl amine, N-acetyl-d-glucosamine (GlcNAc). Radical polymerization of the glycomonomers gave a series of glycopolymers displaying various sugar densities, which were models of the core structure of Asn-linked-type glycoproteins. In addition, fluorometric analyses of wheat germ agglutinin (WGA) against the glycopolymers were carried out, and the results showed unique binding specificities on the basis of flexibility of sugar moieties.

Synthetic assembly of a series of glycopolymers having sialyl α2-3 lactose moieties connected with longer spacer arms

Glycopolymers having sialyl α2-3 lactose moieties via longer spacer arms were systematically prepared from the corresponding glycomonomers. Radical polymerization of glycomonomers gave a series of glycopolymers displaying various sugar densities. Fluorometric analyses of wheat germ agglutinin (WGA) against the glycopolymers were conducted and the results showed unique binding specificities on the basis of sugar densities.

AFM dendritips functionalized with molecular probes specific to cell wall polysaccharides as a tool to investigate cell surface structure and organization

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Functionalisation of AFM dendritips with conA, WGA and anti-β-1,3/β-1, 6-glucan antibodies.

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Cell wall polysaccharides were immobilized on epoxy-activated glass slides.

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Specific binding of immobilized polysaccharides to functionalized dendritips.

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Functionalized dendritips used as a new tool to probe yeast cell surface.

The yeast cell wall is composed of mannoproteins, β-1,3/β-1, 6-glucans and chitin. Each of these components has technological properties that are relevant for industrial and medical applications. To address issues related to cell wall structure and alteration in response to stress or conditioning processes, AFM dendritips were functionalized with biomolecules that are specific for each of the wall components, which was wheat germ agglutinin (WGA) for chitin, concanavalin A (ConA) for mannans and anti-β-1,3/anti-β-1,6-glucan antibodies for β-1,3/β-1,6-glucans. Binding specificity of these biomolecules were validated using penta-N-acetylchitopentaose, α-mannans, laminarin (short β-1,3-glucan chain) and gentiobiose (2 glucose units linked in β 1→6) immobilized on epoxy glass slides. Dynamic force spectroscopy was employed to obtain kinetic and thermodynamic information on the intermolecular interaction of the binary complexes using the model of Friddle-Noy-de Yoreo. Using this model, transition state distance x_t, dissociate rate k_off and the lowest force (f_eq) required to break the intermolecular bond of the complexes were approximated. These functionalized dendritips were then used to probe the yeast cell surface treated with a bacterial protease. As expected, this treatment, which removed the outer layer of the cell wall, gave accessibility to the inner layer composed of β-glucans. Likewise, bud scars were nicely localized using AFM dendritip bearing the WGA probe. To conclude, these functionalized AFM dendritips constitute a new toolbox that can be used to investigate cell surface structure and organization in response to a wide arrays of cultures and process conditions.

Fluorogenic glycopolymers available for determining the affinity of lectins by intermolecular FRET

A convenient assembly of fluorogenic glycopolymers having various polymer compositions was accomplished from the corresponding glycomonomer and dansyl monomer by means of radical polymerization, and the water-soluble glycopolymers gave typical fluorescence spectroscopic profiles due to the dansyl moieties on the glycopolymer in aqueous media. Biological evaluation of the polymer against wheat germ agglutinin (WGA) was accomplished on the basis of fluorescence changes due to tryptophan residues on WGA, and the affinities between the glycopolymers and WGA were estimated to be 4.7 × 10⁵ to 9.3 × 10⁵ M^-1. In order to apply the fluorogenic glycopolymers for further biological measurements, efficient resonance energy transfer from tryptophan moieties on WGA to dansyl moieties on the fluorogenic glycopolymers was examined. FRET profiles of both fluorophores were similar compared to the binding profiles on the basis of fluorescence changes of tryptophan residues. This approach is applicable for the determination of an affinity constant between a carbohydrate and a lectin in which no fluorophore exists near the binding site.

Preparation of Functional Monomers as Precursors of Bioprobes from a Common Styrene Derivative and Polymer Synthesis

CM-Str (4-(Chloromethyl)styrene) was used as a useful starting material for the construction of a series of functional monomers. Substitution of the chlorine to the corresponding azide was performed, and the reduction of the azide proceeded smoothly to afford an aminostyrene, which was used as a common precursor for the preparation of functional monomers. Condensation of the amine with a fluorophore, biotin and carbohydrate was accomplished. Among the monomers, a carbohydrate monomer was polymerized with or without acrylamide as a model polymerization to yield the corresponding water-soluble glycopolymers, and biological evaluations of the glycopolymers for a lectin, and wheat germ agglutinin (WGA), were carried out on the basis of the fluorescence change of tryptophan in the WGA.

Lactotriaose-containing carbosilane dendrimers: Syntheses and lectin-binding activities

Carbosilane dendrimers periphery-functionalized with lactotriaose (GlcNAcbeta1-3Galbeta1-4Glc) with valencies of three, four, six, and twelve were prepared for use in a lectin-binding assay. A lactotriaose derivative was prepared from D-glucosamine and D-lactose derivatives. The N-Troc-protected glucosamine glycosyl donor and 3'-O-unprotected lactose glycosyl acceptor were condensed in the presence of silver trifluoromethanesulfonate and methylsulfenyl bromide to provide corresponding trisaccharide with new beta-1-3 linkages in 92% yield. The protection group of the trisaccharide was transformed into an acetyl group. The 4-pentenyl glycoside was prepared from the acetate via glycosyl bromide. The alkene was converted into acetyl sulfide by addition of thioacetic acid under radical conditions. The lactotriaose unit was linked with carbosilane dendrimers to afford acetyl-protected glycodendrimers. De-O-acetylation of the dendrimers was carried out in the presence of sodium methoxide and then aq NaOH to give the desired lactotriaose clusters using a carbosilane dendrimer backbone. Their biological activities toward WGA were evaluated by fluorescence methods. The binding constants of free lactotriaose and trivalent, tetravalent, hexavalent, and dodecavalent glycodendrimers to WGA were determined to be 1.1x10(3), 4.4x10(4), 5.1x10(4), 2.8x10(6), and 1.3x10(6) M-1, respectively. The hexavalent glycodendrimer showed a 2500-fold larger binding effect than that of free lactotriaose.

Plant-derived antifungal proteins and peptides

Plants produce potent constitutive and induced antifungal compounds to complement the structural barriers to microbial infection. Approximately 250 000 – 500 000 plant species exist, but only a few of these have been investigated for antimicrobial activity. Nevertheless, a wide spectrum of compound classes have been purified and found to have antifungal properties. The commercial potential of effective plant-produced antifungal compounds remains largely unexplored. This review article presents examples of these compounds and discusses their properties.Key words: antifungal, peptides, phytopathogenic, plants, proteins.

Three-Dimensional Arrangement of Sugar Residues along Helical Polypeptide Backbone. 2. Synthesis of Periodic N-Glycosylated Peptides by Polymerization of Tripeptide Active Esters Containing α,α-Disubstituted Amino Acid

New type of N-glycosylated peptides having periodic sequence of -[X-Gln(beta-D-GlcNAc)-Aib]- [X = L-Glu(OMe), L-Lys(Ac), L-Ala; Aib = alpha-aminoisobutyric acid] were synthesized by polymerization of glycosylated tripeptides with an active ester methods using Cl(-+)H(3)N-L-Glu(OMe)-Gln[beta-D-GlcNAc(Ac)(3)]-Aib-ONp (Np=p-nitrophenyl) (13a), Cl(-+)H(3)N-L-Lys(Ac)-Gln[beta-D-GlcNAc(Ac)(3)]-Aib-ONp (13b), and Cl(-+)H(3)N-L-Ala-Gln[beta-D-GlcNAc(Ac)(3)]-Aib-ONp (13c) as the monomers. Polymerizable glycosylated tripeptides were prepared by stepwise N,N-dicyclohexylcarbodiimide (DCC)/1-hydroxybenzotriazole (HOBt) method. Polymerizations of 13a-c were initiated by triethylamine and proceeded in DMSO at 50 degrees C for 5 days in the presence of 1-hydroxy-7-azabenzotriazole (HOAt) as the activator (conversions were 25-75%). The glycopeptides were deacetylated by hydrazine monohydrate in methanol to afford periodic glycopeptides 14 (12-27 residues) without racemization (yield, 35-89%). CD spectra in methanol, trifluoroethanol, and water of deacetylated glycopolymers 14a, 14b, and 14c showed double minima (206 and 222 nm) of negative Cotton effect indicating that N-glycoside (N-acetyl-d-glucosamine) was arranged three-dimensionally along the alpha-helical peptides in water as well as in organic protic solvents. The helix content depends on the solvent, peptide sequence, and spacer between peptide backbone and sugar. Interaction of the glycopeptides with wheat germ agglutinin (WGA) lectin was investigated by fluorescence measurement.

A novel family of chitin-binding proteins from insect type 2 peritrophic matrix. cDNA sequences, chitin binding activity, and cellular localization

The peritrophic matrix is a prominent feature of the digestive tract of most insects, but its function, formation, and even its composition remain contentious. This matrix is a molecular sieve whose toughness and elasticity are generated by glycoproteins, proteoglycans, and chitin fibrils. We now describe a small, highly conserved protein, peritrophin-15, which is an abundant component of the larval peritrophic matrices of the Old World screwworm fly, Chrysomya bezziana, and sheep blowfly, Lucilia cuprina. Their deduced amino acid sequences code for a 8-kDa secreted protein characterized by a highly conserved and novel register of six cysteines. Two Drosophila homologues have also been identified from unannotated genomic sequences. Recombinant peritrophin-15 binds strongly and specifically to chitin; however, the stoichiometry of binding is low (1:10,000 N-acetyl glucosamine). We propose that peritrophin-15 caps the ends of the chitin polymer. Immunogold studies localized peritrophin-15 to the peritrophic matrix and specific vesicles in cells of the cardia, the small organ of the foregut responsible for peritrophic matrix synthesis. The vesicular contents are disgorged at the base of microvilli underlying the newly formed peritrophic matrix. This is the first time that the process of synthesis and integration of a peritrophic matrix protein into the nascent peritrophic matrix has been observed.

Horseshoe crab hemocyte-derived antimicrobial polypeptides, tachystatins, with sequence similarity to spider neurotoxins

Antimicrobial peptides, named tachystatins A, B, and C, were identified from hemocytes of the horseshoe crab Tachypleus tridentatus. Tachystatins exhibited a broad spectrum of antimicrobial activity against Gram-negative and Gram-positive bacteria and fungi. Of these tachystatins, tachystatin C was most effective. Tachystatin A is homologous to tachystatin B, but tachystatin C has no significant sequence similarity to tachystatins A and B. Tachystatins A and B showed sequence similarity to omega-agatoxin-IVA of funnel web spider venom, a potent blocker of voltage-dependent calcium channels. However, they exhibited no blocking activity of the P-type calcium channel in rat Purkinje cells. Tachystatin C also showed sequence similarity to several insecticidal neurotoxins of spider venoms. Tachystatins A, B, and C bound significantly to chitin. A causal relationship was observed between chitin binding activity and antifungal activity. Tachystatins caused morphological changes against a budding yeast, and tachystatin C had a strong cell lysis activity. The septum between mother cell and bud, a chitin-rich region, was stained by fluorescence-labeled tachystatin C, suggesting that the primary recognizing substance on the cell wall is chitin. As horseshoe crab is a close relative of the spider, tachystatins and spider neurotoxins may have evolved from a common ancestral peptide, with adaptive functions.

A FTIR spectroscopy evidence of the interactions between wheat germ agglutinin and N-acetylglucosamine residues

Wheat germ agglutinin (WGA), a lectin binding a N-acetyl-D-neuraminic acid (NeuNAc) and/or N-acetyl-D-glucosamine (GlcNAc) group, was studied by Fourier transform infrared (FTIR) spectroscopy. Deconvolution of the FTIR spectrum of WGA alone indicated the presence of few alpha-helices and beta-sheets, in contrast to many other lectins. These results agree with previous WGA crystal data. The WGA conformational changes, induced by GlcNAc-bearing liposomes or GlcNAc oligomers, were studied by infrared differential spectroscopy. The GlcNAc binding to WGA resulted in a decrease of turns and alpha-helices and a concomitant appearance of beta-sheets, inducing more or less peptidic N-H deuteration.

Fusarium sp. growth inhibition by wheat germ agglutinin

The antifungal role of wheat germ agglutinin (WGA) isolated from a Romanian dihaploid variety of wheat against two pathogenic fungal species of Fusarium, F. graminearum and F. oxysporum, is demonstrated. WGA was prepared from unprocessed wheat germs by a new purification procedure using chitin and fetuin-Sepharose as affinity chromatography supports. SDS-PAGE and chitinase assay showed that the WGA preparation migrated as a single protein band and was devoid of any contaminating enzyme chitinase, well known for its antifungal effects. Based on its affinity for N-acetylglucosamine residues, WGA binding to the chitin-containing walls of the fungi was detected by fluorescence microscopy using WGA coupled with fluorescein isothiocyanate (FITC). In vitro testing of WGA action on early developmental stages of both fungal strains resulted in various modifications of the germ tubes, visualised by light microscopy: swelling, vacuolation of the cellular content and lysis of cell walls. Viability tests performed on potato tuber slices showed that the microbial infection was prevented from spreading by pretreatment of the fungal suspension with WGA.

Differences in hydropathic properties of ligand binding at four independent sites in wheat germ agglutinin-oligosaccharide crystal complexes

The binding interactions of N-acetyl-D-neuraminic acid and N,N' diacetyl-chitobiose (GlcNAc-beta-1,4-GlcNAc), observed in crystal complexes of wheat germ agglutinin (WGA) at four independent sites/monomer, were analyzed and compared with the modeling program HINT (Hydropathic INTeractions). This empirical method allows assessment of relative ligand binding strength and is particularly applicable to cases of weak binding where experimental data is absent. Although the four WGA binding sites are interrelated by a fourfold sequence repeat (eight sites/dimer), similarity extends only to the presence of an aromatic amino acid-rich pocket and a conserved serine. Strong binding requires additional interactions from a contacting domain in the second subunit. Ligand positions were either derived from crystal structures and further optimized by modeling and molecular mechanics, or from comparative modeling. Analysis of the overall HINT binding scores for the two types of ligands are consistent with the presence of two high-affinity and two low-affinity sites per monomer. Identity of these sites correlates well with crystal structure occupancies. The high-affinity sites are roughly equivalent, as predicted from solution binding studies. Binding scores for the low-affinity sites are weaker by at least a factor of two. Quantitative estimates for polar, nonpolar, and ionic interactions revealed that H-bonding makes the largest contribution to complex stabilization in the seven bound configurations, consistent with published thermodynamic data. Although the observed nonpolar interactions are small, they may play a critical role in orienting the ligand optimally.

Site-directed mutagenesis and sugar-binding properties of the wheat germ agglutinin mutants Tyr73Phe and Phe116Tyr

Wheat germ agglutinin is a dimeric lectin composed of two identical subunits. Each subunit consists of four homologous hevein-like domains of 42 or 43 amino acids each. Amino acid residues at the same position in each domain involved in sugar binding are thought to play a similar role in sugar binding. In order to clarify the role of the amino acid residue at domain position 30 of wheat germ agglutinin isolectin 2 (WGA2) in sugar binding, two WGA2 variants each containing a mutation, either Tyr73-->Phe (domain B) or Phe116-->Tyr (domain C), were produced. The binding activity for (GlcNAc)3 and the three-dimensional structure of these mutants were characterized by comparing with the properties of wild-type WGA2. Equilibrium dialysis experiments using (GlcNAc)3 indicated that the mutation Tyr73-->Phe reduced the overall sugar-binding activity at both pH 5.9 and pH 4.7. In addition, positive cooperativity toward (GlcNAc)3 binding was observed at pH 4.7. In contrast, the mutation of Phe116-->Tyr increased the overall sugar-binding activity at pH 5.9, but reduced this activity at pH 4.7 without changing the number of sugar-binding sites. Positive cooperativity was not observed at pH 5.9 or pH 4.7. X-ray crystallographic analysis of mutant WGA2 revealed that the mutation of Tyr73-->Phe caused a side chain movement of the Glu115 residue of the opposite subunit that formed a hydrogen bond with Tyr73 in wild-type WGA2. No changes were observed in the backbone structure and the disposition of the benzene ring of Phe73. The mutation Phe116-->Tyr caused the formation of a new hydrogen bond between Tyr116 and Glu72 of the opposite subunit. The changes in the sugar-binding properties in WGA2 mutants are discussed in relation to the structural change at the binding site.

Purification of rat liver plasma membranes by wheat-germ-agglutinin affinity partitioning

Rat liver plasma membranes were separated from other cellular membranes by affinity partitioning in an aqueous polymer two-phase system by using the lectin wheat-germ agglutinin covalently bound to dextran as the affinity ligand. In borate buffer the bulk of membranes partitioned in the poly(ethylene glycol)-rich top phase, whereas plasma membranes were pulled selectively into the dextran-rich bottom phase in the presence of ligand. The purity and yield of plasma membranes prepared by lectin affinity partitioning and by conventional sucrose-density-gradient centrifugation was similar, as judged from marker-enzyme activities. The affinity procedure, not dependent on lengthy centrifugations, is fast and gentle and will be advantageous when studying labile components.

The binding of N-trifluoroacetyl chito-oligosaccharides to wheat-germ agglutinin: a fluorescence investigation

We describe the synthesis of N-trifluoroacetyl chito-oligosaccharides and their use as ligands to probe the binding sites of wheat-germ agglutinin, a lectin specific for N-acetylglucosamine. The binding is monitored using intrinsic protein fluorescence, which is due to tryptophan side-chains. We present arguments purporting to show the presence of a fluorophore close to each of the four sites. The binding of chito-oligosaccharides to wheat-germ agglutinin is complex and can only be approximately described by an independent and equivalent sites model. This model applies when the ligand concentration range is restricted to higher values. The possible role of ligand-mediated protein aggregation and of site inequivalence is discussed. We find that the affinity of trifluoroacetylated chito-oligosaccharides for wheat-germ agglutinin is higher than that of the N-acetylated parent compounds, the difference increasing with chain length. Our results are in agreement with a model of the binding site previously proposed by Clegg et al. (Biochemistry 22 (1983) 4797-4804).

Studies on tryptophan residues of Abrus agglutinin. Stopped-flow kinetics of modification and fluorescence-quenching studies

The presence of two essential tryptophan residues/molecule was implicated in the binding site of Abrus agglutinin [Patanjali, Swamy, Anantharam, Khan & Surolia (1984) Biochem. J. 217, 773-781]. A detailed study of the stopped-flow kinetics of the oxidation of tryptophan residues revealed three classes of tryptophan residues in the native protein. A discrete reorganization of tryptophan residues revealed three classes of tryptophan residues in the native protein. A discrete reorganization of tryptophan residues into two phases was observed upon ligand binding. The heterogeneity of tryptophan exposure was substantiated by quenching studies with acrylamide, succinimide and Cs+. Our study revealed the microenvironment of tryptophan residues to be hydrophobic, and also the presence of acidic amino acid residues in the vicinity of surface-localized tryptophan residues.

Comparative binding of wheat germ agglutinin and its succinylated form on lymphocytes

We have compared the binding parameters of native wheat germ agglutinin (WGA) and its succinylated form (SWGA) to rat lymphocytes. Scatchard plots were obtained with the fluoresceinated lectins in a concentration range of 10 nM to 0.1 mM. Association and dissociation rate parameters were also measured. The following differences were observed: at low concentration of WGA, binding is positively cooperative with a Hill coefficient of 1.75, whereas binding of SWGA is not. The numbers of high-affinity sites are respectively (2.5 +/- 0.8) X 10(6) and (6.4 +/- 1.3) X 10(5) for WGA and SWGA. Association constants were found to be (4.7 +/- 1.7) X 10(6) l mol-1 for WGA and (1.42 +/- 0.36) X 10(7) l mol-1 for SWGA, which is 35 times higher than for native WGA. Neuraminidase treatment decreases the Hill coefficient as well as the number of sites involved in the cooperative binding of native WGA. Equilibrium data were obtained at three temperatures to determine the thermodynamic parameters (delta H degree and delta S degree). These results are indicative of an oligomerization process dynamically formed at the membrane level before tight binding of the lectin to its receptors could occur.

Interaction of rice (Oryza sativa) lectin with N-acetylglucosaminides. Fluorescence studies

The interaction of lectin isolated from rice (Oryza sativa) embryos with N-acetylglucosaminides was studied by equilibrium dialysis and fluorescence. Equilibrium dialysis with 4-methylumbelliferyl-(GlcNac)2 showed that rice lectin (Mr 38000) contains four equivalent saccharide-binding sites. Addition of the N-acetylglucosaminides GlcNac, (GlcNac)2 and (GlcNac)3 enhanced the intrinsic fluorescence of rice lectin and this was accompanied by a 10nm blue-shift of its maximum fluorescence with (GlcNac)2 and (GlcNac)3. These changes in intensity allowed determination of the association constants, which increased with the number of saccharide units: at 20 degrees C, Ka = (1.3 +/- 0.1) X 10(3), (5.1 +/- 0.4) X 10(4) and (2.6 +/- 0.1) X 10(5) M-1 for GlcNac, (GlcNac)2 and (GlcNac)3 respectively. The binding enthalpy, delta H0, for the three glucosaminides were very low and ranged from -12.1 to -20.6 kJ X mol-1. The results are compared with those obtained with wheat-germ agglutinin, another GlcNac-specific gramineaous lectin.

Wheat germ agglutinin dimers bind sialyloligosaccharides at four sites in solution: proton nuclear magnetic resonance temperature studies at 360 MHz

Equilibrium binding studies have been performed over a range of temperatures from 25.4 to 47.3 degrees C between wheat germ agglutinin isolectin I (WGA I) and the alpha 2-3 isomer of (N-acetylneuraminyl)lactose (NeuNAc alpha 2-3Gal beta 1-4G1c). Proton nuclear magnetic resonance spectroscopy at 360 MHz has been used to monitor titrations in this system under conditions where the fraction of total ligand which is bound is small, yet the fractional occupation of sites covers a wide range. Several of the ligand resonances, including the N-acetyl methyl and the axial and equatorial hydrogens at carbon 3 of the NeuNAc residue, are shifted and broadened in the presence of WGA due to chemical exchange between the free and bound environments. The lifetime broadening of the N-acetyl resonance at room temperature of a series of related sialyloligosaccharides has been previously used by us to measure binding affinities to two WGA isolectins [Kronis, K.A., & Carver, J.P. (1982) Biochemistry 21, 3050-3057]. In this paper we report the temperature dependence of the apparent bound shifts and the apparent bound line widths of the N-acetyl, H3a, and H3e peaks. The true bound shifts for the three resonances have been obtained from these data by using the equations derived by Swift and Connick [Swift, T.J., & Connick, R.E. (1962) J. Chem. Phys. 37, 307-320]. The total bound shifts, per monomer, were found to be -1.98, -4.0, and -0.8 ppm for the N-acetyl, the H3a, and the H3e resonances, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of human lymphocyte activation by wheat germ agglutinin: a model for saccharide-specific suppressor factors

The suppressive effect of wheat germ agglutinin (WGA) on lectin-stimulated blastogenesis and immunoglobulin production was studied. Addition of WGA at 10 micrograms/ml inhibited phytohemagglutinin (PHA)-, concanavalin-A (Con-A)-, and pokeweed mitogen (PWM)-induced mitogenic responses by 70-80%. PWM-driven immunoglobulin synthesis was suppressed by 45% with WGA. The inhibitory effects of WGA were not due to cell death or to interference with lectin binding at the cell surface. Inhibition was dependent on the presence of WGA in the cell culture during the first 24 hr of mitogen exposure and was observed in cultures of both monocyte-depleted peripheral blood mononuclear cells as well as T-cell-enriched populations. WGA-induced inhibition of blastogenesis was blocked by the addition of N-acetylglucosamine (GluNAc) which prevents WGA binding to the cell surface. WGA was found to mimic the suppressive effect of a soluble immune suppressor supernatant (SISS) derived from Con-A-activated mononuclear cell cultures. PHA responses were inhibited by 80 and 95% with SISS and WGA, respectively. The inhibition by both WGA and SISS was totally reversed with addition of GluNAc. Furthermore, WGA and SISS demonstrated competition for the same cell surface receptor site. WGA may therefore be useful as an in vitro model of a saccharide-specific, biologically relevant, soluble mediator for the investigation of mechanisms of immunologic suppression.

The chemical modification of tryptophan residues of alpha-mannosidase from Phaseolus vulgaris

Reaction of alpha-mannosidase (alpha-D-mannoside mannohydrolase, EC 3.2.1.24) from Phaseolus vulgaris with N-bromosuccinimide or 2-hydroxy-5-nitrobenzyl bromide- resulted in loss of enzyme activity. Spectral absorption and fluorescence studies, as well as amino acid analysis, suggested that only tryptophan residues had been modified. No change in conformation could be detected by density gradient ultracentrifugation or circular dichroism of alpha-mannosidase modified by N-bromosuccinimide to virtually zero enzyme activity. The inhibition was partly offset by the substrate analogue alpha-methyl-D-mannoside and the competitive inhibitor mannono-1,4-lactone. Concomitantly, two tryptophan residues fewer were oxidized per molecule. After modification V was reduced, while Km seemed unchanged. Further, there was found evidence for the enzyme having a secondary structure dominated by beta-pleated sheets.