Large scale preparation of wheat germ agglutinin

Oligosaccharides on living human neuroblastoma cells of dissimilar degrees of differentiation. A flow-cytometric study with sugar-specific lectins and glycosidases

The present study is an attempt to correlate cell-surface saccharide composition and/or disposition with malignant behavior and differentiation of two established human neuroblastoma sublines. The methodology applied was quantitative flow-cytometric evaluation of binding data for sugar-specific lectins in conjunction with cell-surface modification by specific glycosidases. The relevant parameters were both the number of binding sites and their apparent affinity constants for the respective lectins on native cells as well as the expected shift of those values after sequential treatment with specific glycosidases. The main conclusions from the findings may be summarized as follows: 1. There appears to exist a correlation between differentiation and/or maturation of neural cells and their cell-surface oligosaccharide patterns, as deduced indirectly by the biophysical approach of quantitative evaluation of lectin-binding data. More specifically, our findings support the hypothesis of a strong correlation between the degree of sialylation of terminal saccharide structures and the relative immaturity and/or lack of differentiation of the respective cells by morphological and biochemical criteria. 2. The combined application of specific lectins and glycosidases should be further exploited for similar purposes since it yields unequivocal information, provided that all biochemical and biophysical methods are scrutinized for their specificity. 3. Flow cytometry with fluorescence-labeled lectins is especially suited for the purposes mentioned since it allows quantitative binding studies to be conducted in a quick and uncomplicated manner. Most importantly, these data can be derived from intact living cells.

Alterations in cell surface carbohydrate composition of a human colon carcinoma cell line affect adhesion to extracellular matrix components

The adhesion of HT29 human colon adenocarcinoma cells to different extracellular matrix components was studied. While treatment of the cells with sialidase had no detectable effect on binding to laminin and fibronectin, attachment to collagen IV was decreased. However, additional removal of beta-(1-4)-bound galactose led to significantly reduced binding to all of the substrates, including fibronectin and laminin. Tunicamycin treatment, monitored by lectin-induced aggregation, drastically diminished cell adhesion to laminin and fibronectin, whereas cell binding to collagen IV was not affected. Arg-Gly-Asp (RGD)-related peptides were used to study the adhesion to collagen IV. The results show that a serine-containing RGD-related peptide GRGDSP has virtually no effect on colon carcinoma cell adhesion to type IV collagen. In contrast, when serine was substituted for threonine (GRGDTP) adhesion to collagen IV was strongly inhibited. After incubation of sialidase-treated cells with the threonine-containing peptide adhesion was almost totally blocked. These results demonstrate the existence of both RGD-dependent and carbohydrate-based mechanisms for metastatic human HT29 cell binding to collagen IV.

Sialic acid dependent cell adhesion to collagen IV correlates with in vivo tumorigenicity of the human colon carcinoma sublines HCT116, HCT116a and HCT116b

Cell surface sialylation of three metastasizing sublines HCT116, HCT116a and HCT116b of a human colon carcinoma was shown to correlate with their in vivo tumorigenicity. Lectin binding studies revealed further differences in cell surface glycosylation between HCT116a and HCT116 sublines. Binding to collagen IV correlated with the in vivo aggressiveness of the cells, whereas binding to fibronectin did not. On a laminin substrate the most tumorigenic line adhered best, but binding of the other lines was similar. Sialidase treatment of the cells had no effect on cell binding to laminin and fibronectin, but resulted in a decrease of cell binding to collagen IV.

Comparison of the refined crystal structures of two wheat germ isolectins

The crystal structures of two closely related members of the multigene family of wheat lectins (isolectins 1 and 2) have been compared. These isolectins differ at five sequence positions, one being located in the saccharide binding site modulating ligand affinity. Crystals of the two isolectins are closely isomorphous (space group C2). The atomic models are based on structure refinement at 1.8 A resolution in the case of isolectin 2 (WGA2) and 2.0 A resolution in the case of isolectin 1 (WGA1). Refinement results for WGA1, recently completed with a crystallographic R-factor of 16.5% (Fo greater than 3 sigma (Fo)), are presented. Examination of a difference Fourier map, [FWGA2-FWGA1], at 2.0 A resolution and direct superposition of the two models indicated an overall close match of the two structures. Local differences are observed in the region of residues 44 to 69, where three sequence differences occur, and at highly mobile external residues on the surface. The average positional discrepancy (root-mean-square delta r) for corresponding protein atoms in the two crystal structures is 0.64 A for independent protomer I and 0.61 A for protomer II (0.29 A and 0.30 A for main-chain atoms). The mean atomic temperature factors are very similar 20.9 versus 22.0 A2). Regions of high flexibility coincide in the two isolectin structures. Of the 210 water sites identified in WGA1, 144 have corresponding positions in WGA2. A set of 51 well-ordered sites was found to be identical in the two independent environments in both structures, and was considered to be important for structure stabilization. Both of the unique sugar binding sites superimpose very closely, exhibiting root-mean-square positional differences ranging from 0.29 A to 0.42 A. The side-chains of the critical tyrosine residues, Tyr73 (P-site) and Tyr159 (S-site), superimpose best, while other highly flexible aromatic groups (Tyr64 and Trp150) and several water sites display large differences in position (0.5 to 1.0 A) and high temperature factors. The aromatic side-chains of Tyr66 in WGA1 and His66 in WGA2 are oriented similarly.

Refinement of the crystal structure of wheat germ agglutinin isolectin 2 at 1.8 A resolution

The crystal structure of wheat germ agglutinin isolectin 2 has been refined by the restrained least-squares method of Hendrickson & Konnert (1980). The asymmetric unit of the C2 crystals contains two chemically identical promoters related by a non-crystallographic 2-fold screw operation. A total of 2290 protein atoms and 186 ordered water sites refined to a final R-factor of 0.179 and an average B-value of 21.6 A2, using 54% (15,601) of the total possible number of reflections in the resolution range 8 to 1.8 A with Fo greater than 3 sigma (Fo). The final model conforms to stereochemically correct bond distances and angles with root-mean-square (r.m.s.) values of 0.018 A and 3.3 degrees, respectively. Accuracy of this model is estimated to be 0.20 A on the basis of a Luzzati plot. Main-chain atomic positions in the two independent promoters, designated I and II, agree with an r.m.s. deviation of 0.30 A (0.58 A for all atoms), indicating identical backbone conformation. The largest discrepancies are seen at flexible surface residues. One error was detected in the amino acid sequence at position 41 (Ser), which refined satisfactorily as a Trp. Loss of electron density for residue A171 during the course of refinement suggests either disorder or absence of this C-terminal residue. The conformation of the polypeptide chain, which is folded into four homologous 43-residue domains (A, B, C and D), was analyzed in terms of dihedral angles, backbone hydrogen bond lengths and CA-atom positions. The four domains were found to be very similar according to all these criteria and superposition of their CA-atoms yielded r.m.s. distances ranging from 0.36 to 0.72 A for the six possible comparisons [corrected]. Large deviations (greater than 1.0 A) are only seen in the five-residue segments that link adjacent domains and at the N and C termini. Refinement has also allowed critical examination of each of the two unique sugar binding sites, referred to as "primary" and "secondary" sites, in different lattice environments. While the essential tyrosyl side-chain in each of these sites (Y73, Y159) assumes precise orientation for optimum hydrophobic contact with the N-acetyl methyl group of the sugar ligand, side-chains involved in hydrogen bonds (S62, E115; and S148, D29) were found to be relatively flexible and able to adapt their conformation to changes in environment. Ordered water structure present in these binding sites is not completely analogous in the different environments.(ABSTRACT TRUNCATED AT 400 WORDS)

Preliminary X-ray diffraction results on co-crystals of wheat germ agglutinin with a sialoglycopeptide from the red cell receptor glycophorin A

Diffraction-quality crystals have been obtained for complexes of each of the major wheat germ agglutinin (WGA) isolectins with the tryptic sialoglycopeptide T-5 from the WGA red cell receptor glycophorin A. This octa-glycopeptide possesses a Thr-linked carbohydrate moiety (GalNAc(NeuNAc)-Gal-NeuNAc) with specificity for the WGA binding site. The crystals belong to the orthorhombic space group P2(1)2(1)2 and have unit cell dimensions: a = 112.2 A, b = 51.0 A, c = 63.5 A (isolectin 1); a = 109.0 A, b = 52.3 A, c = 62.4 A (isolectin 2). There are two monomer complexes in each asymmetric unit.

Molecular dynamics of sugars bound to wheat germ agglutinin, as studied by deuterium nuclear magnetic resonance

Deuterium nuclear magnetic resonance is used to delineate the molecular dynamics of sugars bound to a lectin. 2H spin-spin relaxation times (from linewidth measurements) and reorientational correlation times are determined for N-acetylglucosamine specifically-labeled with 2H in the N-acetyl group and at carbon-3 of the pyranoside ring, in the presence and absence of wheat germ agglutinin. The correlation time for the 2H-label of N-acetylglucosamine-3-2H in the bound state is the same as that of the protein (3 X 10(-8)S), indicating that the six-membered ring has negligible motional freedom relative to the protein. The correlation time for the C2H3 group of N-acetyl-2H3-glucosamine (1.7 X 10(-9)S) shows that the N-acetyl side chain is also immobilized in the binding site, the only motion available being rotation of the C2H3 group about its threefold axis.