Fine sugar specificity of the mistletoe (Viscum album) lectin I.

The behaviour of N-acetyllactosamine-type oligosaccharides and glycopeptides on a column of mistletoe lectin I (MLI) immobilized on Sepharose 4B was examined. The immobilized lectin does not show any affinity for asialo-N-glycosylpeptides and related oligosaccharides, which possess one to four unmasked N-acetyllactosamine sequences. However, substitution of at least one of the N-acetyllactosamine sequences by sialic acid residues, either at O-3 or O-6 of galactose, slightly enhances the affinity of the lectin. Such sialylated N-glycosylpeptides or oligosaccharides are eluted from the lectin column by the starting buffer as retarded fractions. Surprisingly, the affinity of the immobilized MLI is higher for P1 antigen-containing glycopeptide isolated from turtle-dove ovomucoid and for glycopeptides from bovine thyroglobulin containing terminal non-reducing Gal alpha 1-3Gal sequences. These structures are strongly bound on the lectin column and their elution is obtained with 0.15 M galactose in the starting buffer.

Structural analysis of the carbohydrate chains isolated from mistletoe (Viscum album) lectin I.

Two glycopeptide fractions prepared from mistletoe (Viscum album) lectin I by Pronase digestion were fractioned by affinity chromatography on a concanavalin A-Sepharose column. With 400-MHz 1H NMR spectroscopy, in conjunction with sugar analysis, the following oligosaccharide structures could be determined: two oligomannose-type glycans in the ratio 4:1, one containing six mannose and the other containing five mannose units, both with two 2-acetamido-2-deoxyglucose units. In addition, a mannotriosyl-->N,N'-diacetylchitobiose glycan containing a xylosyl group and an alpha-fucosyl group (1-->3)-linked to the 2-acetamido-2-deoxyglycosyl-1 residue, a common core element of many plant glycoproteins, was also observed.

Affinity of four immobilized Erythrina lectins toward various N-linked glycopeptides and related oligosaccharides.

The behavior of N-acetyllactosamine-type oligosaccharides and glycopeptides on columns of four different Erythrina agglutinins immobilized on Sepharose was examined. The sugar-binding specificity of the four lectins is very similar and is directed toward unmasked N-acetyllactosamine sequences, the main difference between the four lectins being the relative strength of interaction of the lectins with a given glycan. Substitution of the N-acetyllactosamine sequences by sialic acid residues, either at O-3 or O-6 of galactose completely abolishes the affinity of the lectins for the saccharides. The presence of one or several alpha-Fuc-(1----3)-GlcNAc groups decreases or completely inhibits the interaction between the glycopeptides and the Erythrina lectins. Substitution of the beta-mannose residue by an additional bisecting beta-(1----4)-N-acetylglucosamine residue decreases the affinity of the lectins for these structures as compared to the unsubstituted ones. Surprisingly, the affinity of the lectins for the oligosaccharides tested is higher than for the corresponding glycopeptides. Our findings show that, after careful calibration with well-defined oligosaccharides and glycopeptides, the immobilized Erythrina agglutinin-Sepharose columns provide valuable tools for the fractionation of N-acetyllactosamine-containing oligosaccharides and glycopeptides.