Lectin structure-activity: the story is never over.

Advances in plant lectin biochemistry have made great strides during the past decade. Technical advances in biophysical techniques and molecular biology, the availability of synthetic oligosaccharides, and characterization of lectins with unique carbohydrate-binding properties are responsible for these advances. Studies in this laboratory support the view that interesting new discoveries are yet to be made. A new lectin was recently isolated from a fungus (Polyporous squamosus) that recognizes the Neu5Ac alpha2,6 Gal beta1,4 GlcNAc/Glc trisaccharide epitope with high affinity. The lectin does not interact with alpha2,3-linked Neu5Ac or Neu5Ac alpha2,6 GalNAc groups as occur in ovine submaxillary mucin. An unusual lectin with two distinctly different carbohydrate-binding sites is present in tubers of Xanthosoma sagittifolium (L). One species of sites recognizes clusters of oligomannosyl residues. The other type of binding site best accommodates a nonsialylated, triantennary oligosaccharide having LacNAc or Lacto-N-biose (Gal beta1,3GlcNAc) groups at its three nonreducing termini. The banana lectin has also been studied. It recognizes both alpha and beta1,3-linked glucosyl oligosaccharides, generates a precipitin curve with the branched trisaccharide Man alpha1,6[Man alpha1,3]Man, and binds to beta-glucans containing beta1,6-glucosyl end groups.