Improved procedures for purification of the Bandeiraea simplicifolia I isolectins and Bandeiraea simplicifolia II lectin by affinity chromatography

Identification of novel plasma glycosylation-associated markers of aging

The pro- or anti-inflammatory activities of immunoglobulins G (IgGs) are controlled by the structure of the glycan N-linked to Asn₂₉₇ of their heavy chain. The age-associated low grade inflammation (inflammaging) is associated with increased plasmatic levels of agalactosylated IgGs terminating with N-acetylglucosamine (IgG-G0) whose biogenesis has not been fully explained. Although the biosynthesis of glycans is in general mediated by glycosyltransferases associated with internal cell membranes, the extracellular glycosylation of circulating glycoproteins mediated by plasmatic glycosyltransferases has been recently demonstrated. In this study we have investigated the relationship between plasmatic glycosyltransferases, IgG glycosylation and inflammatory and aging markers. In cohorts of individuals ranging from infancy to centenarians we determined the activity of plasmatic β4 galactosyltransferase(s) (B4GALTs) and of α2,6-sialyltransferase ST6GAL1, the glycosylation of IgG, the GlycoAge test (a glycosylation-based marker of aging) and the plasma level of inflammatory and liver damage markers. Our results show that: 1) plasmatic B4GALTs activity is a new marker of aging, showing a linear increase throughout the whole age range. 2) plasmatic ST6GAL1 was high only in children and in people above 80, showing a quadratic relationship with age. 3) Neither plasmatic glycosyltransferase correlated with markers of liver damage. 4) plasmatic ST6GAL1 showed a positive association with acute phase proteins in offspring of short lived parents, but not in centenarians or in their offspring. 5) Although the glycosylation of IgGs was not correlated with the level of the two plasmatic glycosyltransferases, it showed progressive age-associated changes consistent with a shift toward a pro-inflammatory glycotype.

Dual modes of membrane binding direct pore formation by Streptolysin O

Effector translocation is central to the virulence of many bacterial pathogens, including Streptococcus pyogenes, which utilizes the cholesterol-dependent cytolysin Streptolysin O (SLO) to translocate the NAD(+) glycohydrolase SPN into host cells during infection. SLO's translocation activity does not require host cell membrane cholesterol or pore formation by SLO, yet SLO does form pores during infection via a cholesterol-dependent mechanism. Although cholesterol was considered the primary receptor for SLO, SLO's membrane-binding domain also encodes a putative carbohydrate-binding site, implicating a potential glycan receptor in binding and pore formation. Analysis of carbohydrate-binding site SLO mutants and carbohydrate-defective cell lines revealed that glycan recognition is involved in SLO's pore formation pathway and is an essential step when SLO is secreted by non-adherent bacteria, as occurs during lysis of erythrocytes. However, SLO also recognizes host cell membranes via a second mechanism when secreted from adherent bacteria, which requires co-secretion of SPN but not glycan binding by SLO. This SPN-mediated membrane binding of SLO correlates with SPN translocation, and requires SPN's non-enzymatic domain, which is predicted to adopt the structure of a carbohydrate-binding module. SPN-dependent membrane binding also promotes pore formation by SLO, demonstrating that pore formation can occur by distinct pathways during infection.

Facile preparation of the alpha-Gal-recognizing Griffonia simplicifolia I-B4 isolectin

The B4 isolectin from Griffonia simplicifolia is of great utility as a reagent for the identification of alpha-D-galactopyranosyl end groups. Its separation from isolectins containing A subunits has been greatly improved by a simple, rapid procedure using a column of N-acetylgalactosamine coupled to vinyl sulfone-activated Sepharose 4B to selectively retain the A subunit-containing isolectins. The procedure has the advantages over previous affinity procedures of speed (the isolation of B4 isolectin can be achieved in one day), simplicity, and high degree of resolution of the B4 isolectin.

The role of valence on the high-affinity binding of Griffonia simplicifolia isolectins to type A human erythrocytes

The Griffonia simplicifolia-I (GS-I) isolectins have been used to probe the effect of lectin valence on their high-affinity binding to human erythrocytes. These tetrameric lectins are composed of A and B subunits and constitute a series of five isolectins (A4, A3B, A2B2, AB3, B4). The A subunit is specific for alpha-D-GalNAc end groups and binds to the blood type A determinant GalNAcalpha1, as well as to terminal alpha-D-Gal groups found on type B cells. The B subunit is specific for alpha-D-Gal end groups, and binds very specifically to type B erythrocytes. This series of isolectins is tetravalent (A4), trivalent (A3B), divalent (A2B2), and monovalent (AB3) for type A erythrocytes; thus, this system provides the opportunity to examine the effect of lectin valency on the association constants of these GS-I isolectins binding to cells. Cell binding experiments carried out using 125I-labeled GS-I isolectins and type A human erythrocytes allowed us to demonstrate that (1) the association constant of the isolectin monovalent for alpha-D-GalNAc (AB3) is virtually identical to its association constant for the haptenic sugar methyl-N-acetyl-alpha-D-galactosaminide, reported previously, and (2) the association constant of the GS-I isolectins for human type A erythrocytes increases with increasing valency of the isolectin. These results indicate that the increased affinity displayed by the GS-I isolectins for human type A erythrocytes is dependent on their multivalency, and not on an extended binding site nor on nonspecific, or noncarbohydrate, interactions of the lectin with the cell surface. These findings should be of general relevance to understanding the high-affinity interactions observed between other multivalent proteins and multivalent ligands (e.g., cell surfaces).

Purification of a protein from Agrobacterium tumefaciens strain A348 that binds phenolic compounds

In order to induce tumours on dicotyledonous plants, the bacterium Agrobacterium tumefaciens needs to be able to sense signal molecules, i.e. phenolic compounds. In order to identify putative chemoreceptors or environmental sensors involved in vir gene induction, we undertook the purification of a phenol-binding protein by affinity chromatography on a syringamide Ultrogel A4 column equilibrated at pH 5.6. A mild extraction of bacterial proteins with a Tris/HCl buffer at pH 9.0 led to the purification of a 39 kDa protein (Pbp39) with a pl of 4.3 after specific elution of the affinity matrix with sodium syringate. When the affinity chromatography was performed at neutral pH, barely any protein was isolated, indicating the importance of an acidic pH for optimal affinity. A microplate binding experiment revealed that both syringlyl biotinylated-BSA and sinapyl-biotinylated-BSA bound at pH 5.6 to the plate coated with Pbp39.

The lectin Griffonia simplicifolia I-A4 (GS I-A4) specifically recognizes terminal alpha-linked N-acetylgalactosaminyl groups and is cytotoxic to the human colon cancer cell lines LS174t and SW1116

The lectin GS I-A4 binds to terminal alpha-N-acetylgalactosaminyl (GalNAc) groups (which include the Tn antigen), but not to the closely related tumor-associated epitope, sialylated Tn antigen. The lectin also precipitates asialo OSM, but not its native sialylated form. Lectin histochemistry with human colonic tissues showed that GS I-A4 specifically stained specimens of colon cancer and colonic tissues from individuals with FAP; however, normal colonic tissues from patients without colonic disease were rarely stained with this lectin. Glycoconjugates bound by GS I-A4 were observed on the surface membranes of 2 human colon cancer cell lines, LS174t and SW1116, when fluorescein isothiocyanate (FITC)-conjugated GS I-A4 was used. GS I-A4 was toxic to these 2 human colon cancer cell lines in monolayer culture. A dose-response study conducted using 10-160 micrograms/ml, of GS I-A4 demonstrated significant dose-related toxicity against LS174t and SW1116 cells. At concentrations > 80 micrograms/ml, > 99% of LS174t and > 90% of SW1116 cells were killed. Four mM GalNAc specifically inhibited the cytotoxic effect of GS I-A4 (p < 0.001), whereas 4mM N-acetylglucosamine (GlcNAc) had no effect. Two other lectins that recognize terminal alpha-GalNAc residues, DBA and LBL, were significantly less cytotoxic to the colon cancer cells than GS I-A4. In the light of these findings, we speculate that GS I-A4 may have potential use as a diagnostic agent against colorectal cancer.

alpha-D-galactose-bearing glycoproteins on the surface of stimulated murine peritoneal macrophages. Biochemical and immunochemical characterization of purified glycoproteins

Two glycoproteins were isolated from lysates of thioglycollate-stimulated, murine peritoneal macrophages by affinity chromatography on immobilized Griffonia simplicifolia I lectin and by preparative SDS/PAGE. The glycoproteins were readily labeled on the surface of intact macrophages with 3H and 125I. The labeled glycoproteins migrated as broad bands of molecular mass 92-109 kDa and 115-125 kDa. The mobility of the glycoproteins decreased only slightly after reduction with dithiothreitol, indicating the absence of intersubunit disulfide bridges. The 92-kDa and 115-kDa glycoproteins had pI 5.2-5.4 and pI less than or equal to 4, respectively. Digestion of both glycoproteins with alpha-galactosidase released 23% of their 3H content and abolished their ability to bind to the G. simplicifolia I lectin, showing that they contain terminal alpha-D-galactosyl groups. After reduction with 2-mercaptoethanol, each glycoprotein fraction was sensitive to N-glycanase; the 115-kDa glycoproteins produced a smear with the front at approximately 67 kDa, whereas the 92-kDa glycoprotein gave two bands of 61 kDa and 75 kDa. Unreduced glycoproteins were insensitive to N-glycanase, suggesting the presence of intramolecular disulfide bonds. Although each glycoprotein fraction was sensitive to endoglycosidase H, this enzyme produced only slight changes in molecular mass when compared with N-glycanase. From these results as well as from the specificity of the enzymes involved, it is concluded that each glycoprotein fraction contains complex-type oligosaccharides and a small amount of high-mannose and/or hybrid-type oligosaccharides. While each glycoprotein fraction was bound to Datura stramonium lectin, they failed to react with anti-[i-(Den)] serum and their digestion with endo-beta-galactosidase did not cause a band shift in SDS/PAGE. Taken together, these results suggest the presence of N-acetyllactosamine units which are not arrayed in linear form but occur as single units, bound either to C2 and C6, or to C2 and C4, or both, of outer mannosyl residues on complex-type oligosaccharides. The glycoprotein(s) fraction precipitated with anti-[I (Step)] serum, suggesting the presence of branched lactosaminoglycans. Digestion of both glycoprotein fractions with a mixture of sialidase and O-glycanase did not alter their mobility in SDS/PAGE, suggesting a lack or low content of O-linked trisaccharides and tetrasaccharides. Each glycoprotein fraction was bound specifically to Sambucus nigra and Maackia amurensis immobilized lectins, indicating the presence of sialic acid linked alpha 2,6 to subterminal D-galactose or N-acetylgalactosamine residues, and alpha 2,3 to N-acetyllactosamine residues, respectively.

Alpha-D-galactosylation of surface fucoglycoconjugate(s) upon stimulation/activation of murine peritoneal macrophages

Murine resident macrophages express, on their surface, carbohydrate epitopes which undergo changes during their stimulation/activation as monitored by binding of 125I labelled Evonymus europaea and Griffonia simplicifolia I-B4 lectins. Treatment of the stimulated macrophages with coffee bean alpha-galactosidase abolished binding of the GS I-B4 isolectin and changed the binding pattern of the Evonymus lectin. The affinity (Ka) of Evonymus lectin for alpha-galactosidase-treated macrophages decreased approximately 23-fold, from 1.25 x 10(8) M-1 to 5.5 x 10(6) M-1. Subsequent digestion of alpha-galactosidase-treated macrophages with alpha-L-fucosidase from Trichomonas foetus, further reduced binding of Evonymus lectin. Resident macrophages showed the same pattern of Evonymus lectin binding, with the same affinity, as alpha-galactosidase-treated, stimulated macrophages. These results, together with a consideration of the carbohydrate binding specificity of the Evonymus lectin which, in the absence of alpha-D-galactosyl groups, requires alpha-L-fucosyl groups for binding, indicate the presence, on resident macrophages, of glycoconjugates with terminal alpha-L-fucosyl residues. It is also concluded that during macrophage stimulation/activation alpha-D-galactosyl residues are added to this glycoconjugate and that they form part of the receptor for Evonymus lectin. The same glycoconjugate(s) is/are also expressed on the activated macrophage IC-21 cell line which exhibits the same characteristics as that of stimulated peritoneal macrophages, i.e., it contains alpha-D-galactosyl end groups and is resistant to the action of trypsin. Both lectins were also specifically bound to Corynaebacterium parvum activated macrophages.

Differential expression of glycoproteins containing alpha-D-galactosyl groups on normal human breast epithelial cells and MCF-7 human breast carcinoma cells

Cell surface glycoproteins were isolated from the lysates of 125I-labeled normal human mammary epithelial cells (NHMEC) and from the human breast carcinoma cell line MCF-7, of blood-group O phenotype, by affinity chromatography on Griffonia simplicifolia I lectin-Sepharose. Specific elution of glycoproteins from the column with methyl alpha-D-galactoside suggests the presence of alpha-D-galactosyl groups on these moieties. SDS-PAGE analysis of isolated glycoproteins revealed both quantitative and qualitative differences between glycoproteins from normal and malignant cells. Three major glycoproteins of Mr 180 kDa, 85 kDa and the 44 kDa were obtained from MCF-7 cells. The 180-kDa glycoprotein was absent in NHMEC and the 44-kDa glycoprotein was very weakly expressed in these cells. The only glycoprotein which was found in almost equal amount in the lysate from both normal and malignant cells was the 85-kDa glycoprotein. These results indicate differences between normal human mammary epithelial cells and one kind of malignant human mammary epithelial cells, in the expression of glycoproteins containing alpha-D-galactosyl groups, irrespective of blood-group phenotype; they also demonstrate that alpha-D-galactosyl group are expressed in a very restrictive manner on the surface of this tumor cell line.

Erythrocyte-binding studies on an acidic lectin from winged bean (Psophocarpus tetragonolobus)

An acidic lectin (WBA II) was isolated to homogeneity from the crude seed extract of the winged bean (Psophocarpus tetragonolobus) by affinity chromatography on lactosylaminoethyl-Bio-Gel. Binding of WBA II to human erythrocytes of type-A, -B and -O blood groups showed the presence of 10(5) receptors/cell, with high association constants (10(6)-10(8) M-1). Competitive binding studies with blood-group-specific lectins reveal that WBA II binds to H- and T-antigenic determinants on human erythrocytes. Affinity-chromatographic studies using A-, B-, H- and T-antigenic determinants coupled to an insoluble matrix confirm the specificity of WBA II towards H- and T-antigenic determinants. Inhibition of the binding of WBA II by various sugars show that N-acetylgalactosamine and T-antigenic disaccharide (Thomsen-Friedenreich antigen, Gal beta 1-3GalNAc) are the most potent mono- and di-saccharide inhibitors respectively. In addition, inhibition of the binding of WBA II to erythrocytes by dog intestine H-fucolipid prove that the lectin binds to H-antigenic determinant.

Griffonia simplicifolia I isolectin as a functionally monovalent probe for use in flow cytometry

The inherent tendency of lectins to agglutinate cells has limited their use as reagents for the detection of carbohydrate groups on cell surfaces by flow cytometry. In the current study, we demonstrate a method for the use of a fluoresceinated tetrameric isolectin (Griffonia simplicifolia I-A3B, FITC-GS I-A3B) as a functionally monovalent, nonagglutinating probe in flow cytometry. This isolectin contains three A subunits and one B subunit. Both types of subunits bind alpha-D-galactopyranosyl (alpha-D-galp-) end groups with similar affinities; however, the A subunits have a 1,000-fold greater affinity for N-Acetyl-D-galactosamine (GalNAc) than does the B subunit. The addition of low (1-2 mM) concentrations of GalNAc to the FITC-GS I-A3B isolectin results in blockage of the three A subunits without significantly affecting the B subunit; this yields a functionally monovalent probe for the detection of cell surface alpha-D-Galp end groups. This approach has been used to examine two types of cells: Ehrlich ascites tumor cells and rat alveolar macrophages, both of which are known to express cell surface alpha-D-Galp end groups. Lectin binding, as determined by number of positive cells and fluorescence intensity, was dependent upon concentration of the lectin and haptenic sugar. Specificity of the staining was demonstrated by the ability of methyl alpha-D-galactopyranoside (Met alpha-D-Galp) to abolish the binding of the lectin to the cells. Elimination of both GalNAc and Met alpha-D-Galp from the staining solution resulted in agglutination of the cells, indicating that the A subunits were active in the absence of GalNAc.

Purification and saccharide-binding characteristics of a rice lectin

A lectin was purified from rice flour by aqueous extraction followed by precipitation by ammonium sulfate and affinity chromatography on p-aminobenzyl 2-acetamido-2-deoxy-1-thio-beta-D-glucoside-succinyl-aminohexylaminyl -Sepharose 4B. The molecular weight of the lectin is approximately 36,000, as determined by sedimentation-equilibrium analysis. It is a tetramer consisting of two different subunits (Mr = 12,000 +/- 1,000 and 9,000 +/- 1,000). Amino acid analysis indicated that the lectin contains very high proportions of half-cystine, glycine, and glutamic acid. All of the half-cystines are present as -S-S- bridges. The lectin agglutinates human A, B, AB, and O erythrocytes, rabbit erythrocytes, human leukocytes, and is mitogenic to human lymphocytes. The hemagglutinating activity of rice lectin is inhibited by 2-acetamido-2-deoxy-D-glucose, methyl 2-acetamido-2-deoxy-beta-D-glucoside, chitobiose, and chitotriose. N-Acetylneuraminic acid was a noninhibitor, but N-acetylneuramin-(2----3)-lactose showed weak inhibition. The agglutinating activity was also inhibited by various sialoglycoproteins. The immobilized rice-lectin bound glycophorin, alpha 1-acid glycoprotein, and fetuin. Asialoglycophorin, asialofetuin, ovomucoid, and human chorionic gonadotropin were bound only partially to the column.

Binding of Griffonia simplicifolia I lectin to rat pulmonary alveolar macrophages and its use in purifying type II alveolar epithelial cells

We report that the isolectin Griffonia simplicifolia I-B4 isolated from G. simplicifolia seeds binds to rat alveolar macrophages present in frozen sections of lung tissue or bronchoalveolar lavage fluid. G. simplicifolia I-B4 does not bind to alveolar epithelial cells. We established that G. simplicifolia I-B4 binds to the macrophages via interaction with terminal alpha-D-galactopyranosyl residues present on these cells. This was substantiated by demonstrating that binding is inhibited either by the haptenic sugar alpha-D-galactopyranoside or by treating the cells with coffee bean alpha-galactosidase. Because murine laminin is known to contain terminal alpha-D-galactopyranosyl end-groups, and because we found that an anti-laminin antiserum binds to rat alveolar macrophages, we suspect that G. simplicifolia I-B4 may be binding to laminin present on the macrophages. To isolate alveolar type II epithelial cells from rat lungs, we developed a method that utilizes the lectin G. simplicifolia I. When proteinase-derived suspensions of pulmonary cells are incubated with G. simplicifolia I, the macrophages agglutinate and can be removed by filtration through nylon mesh. After incubating the resulting cellular suspension in tissue culture, the adherent cells are 94 +/- 2% (S.D.) type II cells. When compared to cells isolated by repeated differential adherence, the lectin-prepared type II cells have similar morphology and staining characteristics, form domes in monolayers and incorporate similar amounts of palmitate into disaturated phosphatidylcholine. We believe that the procedure outlined in this report provides a simple and effective method to isolate type II alveolar epithelial cells from rat lungs.

Lectin binding studies on murine peritoneal cells: physicochemical characterization of the binding of lectins from Datura stramonium, Evonymus europaea, and Griffonia simplicifolia to murine peritoneal cells

Purified 125I-labeled lectins from Datura stramonium, Evonymus europaea, and Griffonia simplicifolia (I-B4 isolectin) were used to analyze changes in the expression of carbohydrates on the surface of resident (PC) and thioglycollate-stimulated murine (C57B/6J) peritoneal exudate cells (PEC). The lectins from D. stramonium, E. europaea, and G. simplicifolia I-B4 bind specifically to PEC with relatively high affinity (Kd = 5.65 +/- 1.08 X 10(-7) M, 1.08 +/- 0.12 X 10(-8) M, and 1.33 +/- 0.15 X 10(-7) M, respectively). Assuming a single lectin molecule binds to each cell surface saccharide, the number of receptor sites per cell ranged for different cell samples from 22.3 to 50.0 X 10(6), from 3.8 to 4.8 X 10(6), and from 2.0 to 16.8 X 10(6) for D. stramonium, E. europaea, and G. simplicifolia I-B4 lectins, respectively. There were approximately 3- to 7-fold, 16- to 20-fold, and 2- to 20-fold increases in binding capacity for D. stramonium, E. europaea and G. simplicifolia I-B4, respectively, compared to the binding to resident, peritoneal cells. Scatchard plots of the binding of all three lectins to PEC were linear, suggesting that the receptor sites for these lectins are homogeneous and noninteracting. The binding capacity of these lectins to PEC was unchanged after trypsin digestion of cells. The expression of carbohydrates on the surface of PEC was also monitored by an agglutination assay. PEC were agglutinated by all three lectins whereas PC either were not agglutinated or were agglutinated only at high lectin concentrations. On the basis of our knowledge of the carbohydrate binding specificity of the D. stramonium and G. simplicifolia I-B4 lectins, we postulate that, parallel with thioglycolate stimulation, there is an increase in the number of N-acetyllactosamine residues and terminal alpha-D-galactosyl end groups. The blood group B, and H type 1 determinants--DGa1 alpha 1,3[LFuc alpha 1,2]DGa1 beta 1,3(or 4)DGlcNAc and LFuc alpha 1,2DGa1 beta 1,3DG1cNAc, respectively, as well as DGa1 alpha 1,3DGa1 beta 1,3(or 4)DGlcNAc--may be considered to be possible receptors for the E. europaea lectin. These glycoconjugates, present on the surface of peritoneal exudate cells, provide new chemical markers for studying the differentiation of resident peritoneal cells.

2-Substituted methyl alpha-D-galactopyranosides: synthesis and binding affinity for the A and B subunits of the Griffonia simplicifolia I isolectins

The binding affinities of the N-acetyl, N-trifluoroacetyl, N-propionyl, N-formyl, N-benzoyl, N-p-nitrobenzoyl, N-p-aminobenzoyl, and N-methyl derivatives of methyl 2-amino-2-deoxy-alpha-D-galactopyranoside and the 2-O-acetyl, -benzoyl, -benzyl, and -methyl derivatives of methyl alpha-D-galactopyranoside for the A and B subunits of the Griffonia simplicifolia I isolectins have been determined by hapten inhibition analysis of a galactomannan-isolectin precipitation system. Models for these carbohydrate-protein interactions are presented together with an interpretation of the results on the basis of electronic and steric effects.

Laminin distribution in human decidua and immature placenta. An immunoelectron microscopic study (avidin-biotin-peroxidase complex method)

An immunoelectron microscopic study was carried out on human placenta and decidua with the use of preembedding, the avidin-biotin-peroxidase complex technique, and rabbit anti-murine laminin antibody. Laminin was detected in the lamina lucida of basement membrane of placental villi, amniotic membranes, umbilical cord, endometrial glands, and blood vessels. No positive laminin immunostaining was observed in intracytoplasmic organelles. However, positive immunostaining surrounded decidual cells as a more or less continuous linear membrane. It is suggested that laminin, as a component of this basement membrane-like material that has already been reported in decidual cells, may be related to the hormonal stimulation occurring during pregnancy and trophoblastic attachment.

Probing the topography of lectins with site-specific spin-labeled glycosides

Three new spin-labeled glycosides, spin-label I [1-[4-(beta-D-galactopyranosyloxy)phenyl]-3-(2,2,6,6-tetramethyl-1 -oxypiperidin-4-yl)-2-thiourea], spin-label II (2,2,6,6-tetramethyl-1-oxypiperidin-4-yl alpha-D-galactopyranoside), and spin-label III [1-(methyl 2-deoxy-alpha-D-galactopyranosid-2-yl)-3-(2,2,6,6- tetramethyl-1-oxypiperidin-4-yl)-2-thiourea], were investigated as structural probes of Griffonia simplicifolia I isolectins (GS I) A4 and B4, respectively, by electron spin resonance (ESR) and inhibition of guaran isolectin precipitation. The p-aminophenyl beta-galactoside spin-label I was strongly immobilized by the B4 isolectin (Kd = 0.42 mM; 2T parallel = 54.0 +/- 0.3 G), while binding to the A4 isolectin was so weak (KI congruent to 2 mM) that binding was undetectable by ESR. The preference for the B4 isolectin was indicative of a more extended hydrophobic binding locus adjacent to the carbohydrate-specific binding site. The alpha-galactosyl spin-label II bound slightly more strongly to the A4 than to the B4 isolectin, as evidenced in both Kd values and particularly by differences in the degree of immobilization (2T parallel = 53.5 vs. 51.5 G, respectively). The 2-N-substituted methyl galactoside spin-label III was so poor an inhibitor of both isolectins (KI congruent to 1-2 mM) that ESR detection of the bound complex was not feasible. In all cases above, the spin-labels were displaced by specific monosaccharide haptens.

Reexamination of the carbohydrate binding stoichiometry of lima bean lectin

The carbohydrate binding stoichiometry of lima bean lectin component III was reexamined using equilibrium dialysis and quantitative affinity chromatography following limited chemical modification. Equilibrium dialysis employing methyl[2-14C]benzamido-2-deoxy-alpha-D-galactopyranoside as ligand demonstrated that the lectin tetramer bound 4 mol of sugar with Kassoc = 1.44 +/- 0.13 X 10(3) M-1 (T = 5 degrees C, pH 7.0, ionic strength 0.1). The previous report of two sites/tetramer [Bessler, W. and Goldstein, I. J. (1974) Arch. Biochem. Biophys. 165, 444] appears to be the result of partial inactivation of the lectin due to oxidation of essential thiol groups. Following limited chemical modification of the thiol groups by methyl methanethiosulfonate, multiple intermediate forms with reduced affinity for Synsorb A were obtained. The number and hemagglutinating activities of these intermediates provided further support for the presence of four carbohydrate binding sites on lima bean lectin component III.

A structural comparison of the A and B subunits of Griffonia simplicifolia I isolectins

A structural comparison between the A and B subunits of the five tetrameric Griffonia simplicifolia I isolectins (A4, A3B, A2B2, AB3, B4) was undertaken to determine the extent of homology between the subunits. The first 25 N-terminal amino acids of both A and B subunits were determined following the enzymatic removal of N-terminal pyroglutamate blocking groups with pyroglutamate aminopeptidase. Although 21 amino acids were common to both subunits, there were four unique amino acids in the N-terminal sequence of A and B. Residues 8, 9, 17, and 19 were asparagine, leucine, lysine, and asparagine in subunit A and threonine, phenylalanine, glutamic acid, and serine in subunit B. The last six C-terminal amino acids, released by digestion with carboxypeptidase Y, were the same for both subunits: Arg-(Phe, Val)-Leu-Thr-Ser-COOH. Subunit B, which contains one methionyl residue, was cleaved by cyanogen bromide into two fragments, a large (Mr = 31,000) and a small (Mr = 2700) polypeptide. Failure of the small fragment to undergo manual Edman degradation indicated an N-terminal blocking group, presumably pyroglutamate. Both subunits were digested with trypsin and the tryptic peptides were analyzed using reverse-phase HPLC. Tryptic glycopeptides were identified by labeling the carbohydrate moiety of the A and B subunit using sodium [3H] borohydride. Cysteine-containing tryptic peptides were similarly identified by using [1-14C]iodoacetamide. Approximately 30% of the tryptic peptides were common to both subunits. Thus, although the N- and C-terminal regions of A and B are similar, the subunits each possess unique sequences.

Lectin-binding domains on laminin

The nature and location of carbohydrate moieties on the laminin molecule were identified by studying the binding affinity of a series of lectins for purified, protease-derived fragments of laminin. Laminin is a cross-shaped molecule containing three short arms (36 nm) and one long arm (76 nm). All arms contain globular end regions by electron microscopy. Purified fragments of laminin were obtained which (a) lacked the long arm of the molecule but retained the intact short arms, or (b) lacked both the long arm and the globular end regions of the short arms. These two types of fragments differed markedly in lectin-binding capacity. Using the known sugar specificities of the lectins and hapten sugar competition for lectin-binding to laminin fragments, the following conclusions were reached: (a) alpha-D-Galactopyranosyl end groups are markedly enriched in the globular end regions of the short arms compared to the rod-shaped portions of the molecule. (b) alpha-D-Mannopyranosyl residues are present on both the globular end regions and the rod-shaped portions of the molecule. (c) Exposed N-acetyl-D-galactosaminyl end groups are absent or present in low amounts on laminin. (d) (NANA)-(2 leads to 6)-beta-D-Gal-(1 leads to 4)-beta-D-GlcNAc-(1 leads to 2)-D-Man-terminated oligosaccharide units are enriched on the rod-shaped regions of the short arms compared to the globular end regions.

Enzyme-linked lectin assay (ELLA): use of alkaline phosphatase-conjugated Griffonia simplicifolia B4 isolectin for the detection of alpha-D-galactopyranosyl end groups

Alkaline phosphatase has been coupled to Griffonia simplicifolia I B4 isolectin using a one-step glutaraldehyde conjugation procedure. This enzyme-lectin conjugate (AP-GS I-B4) has been used to specifically detect plastic-bound natural and synthetic glycoproteins bearing alpha-D-galactopyranosyl end groups. The extent of reactivity of the AP-GS I-B4 with the glycoproteins appears to be proportional to the number of terminal galactosyl residues present. Furthermore, this assay, termed ELLA (enzyme-linked lectin assay), is specifically inhibitable by low-molecular-weight sugars containing terminal alpha-D-galactosyl groups. The ELLA reactions may be assayed rapidly and objectively by the use of commercially available ELISA-plate using standard filters.

Stimulated macrophages express a new glycoprotein receptor reactive with Griffonia simplicifolia I-B4 isolectin

This paper presents data on reactions of murine macrophages with a variety of lectins, with special focus on Griffonia simplicifolia I-B4 isolectin, the only lectin we tried that distinguishes stimulated macrophages from resident populations. Specificity of Griffonia simplicifolia I reaction with carbohydrate determinants at the cell surface is shown by (i) ability of alpha-galactosidase treatment of intact cells to abolish all lectin binding whereas beta-galactosidase has no effect on lectin binding, (ii) ability of methyl alpha-D-galactopyranoside to completely inhibit lectin binding with methyl alpha-D-galactopyranoside having no effect on lectin binding, (iii) ability of brief treatment of intact cells with trypsin to liberate a glycopeptide but reacts with G. simplicifolia I to form a precipitate that is dissolved by addition of methyl-alpha-D-galactopyranoside or alpha-galactosidase, (iv) ability of methyl alpha-D-galactopyranoside (but no other monosaccharide) to completely inhibit avid binding of macrophages to G. simplicifolia I lectin immobilized on an insoluble support, and (v) ability of immobilized lectin to separate macrophages into highly pure subpopulations of lectin-reactive and lectin-unreactive cells, as shown by examination of fluorescein-labeled lectin-treated cells with phase-contrast/fluorescence microscopy.