The beta1 2-d-xylose and alpha1 3-l-fucose substituted N-linked oligosaccharides from Erythrina cristagalli lectin. Isolation, characterisation and comparison with other legume lectins

Abstract

The carbohydrate moieties of Erythrina cristagalli lectin were released as oligosaccharides by hydrazinolysis, followed by N‐acetylation and reduction with NaB³H₄. Fractionation of the tritium‐labelled oligosaccharide mixture by Bio‐Gel P‐4 column chromatography and high‐voltage borate electrophoresis revealed that it is composed of five neutral oligosaccharides. Structural studies by sequential exoglycosidase digestion in combination with methylation analysis and two‐dimensional ¹H‐NMR showed that the major component was the fucosecontaining heptasaccharide Manα3(Manα6)(Xylβ2)Manβ4GlcNAcβ4(Fucα3)GlcNAcol. This is the first report of such a structure in plant lectins. Small amounts of the corresponding afucosyl hexasaccharide were also identified, as well as three other minor components. The structure of the heptasaccharide shows the twin characteristics of a newly established family of N‐linked glycans, found to date only in plants. The characteristics are substitution of the common pentasaccharide core [Manα3(Manα6)Manβ4GlcNAcβ4GlcNAc] by (1) a d‐xylose residue linked β1 → 2 to the β‐mannosyl residue and (2) an l‐fucose residue linked α1 → 3 to the reducing terminal N‐acetylglucosamine residue. The oligosaccharide heterogeneity pattern for Erythrina cristagalli lectin was also found for the lectins from four other Erythrina species and the lectins of two other legumes, Sophora japonica and Lonchocarpus capassa.