Studies on the binding of wheat germ agglutinin (Triticum vulgaris) to O-glycans

The binding profile of Triticum vulgaris (WGA, wheat germ) agglutinin to 23 O-glycans (GalNAc alpha 1-->Ser/Thr containing glycoproteins, GPs) was quantitated by the precipitin assay and its specific interactions with O-glycans were confirmed by the precipitin inhibition assay. Of the 28 glycoforms tested, six complex O-glycans (hog gastric mucins, one human blood group A active and two precursor cyst GPs) reacted strongly with WGA and completely precipitated the lectin added. All of the other human blood group A active O-glycans and human blood group precursor GPs also reacted well with the lectin and precipitated over two-thirds of the agglutinin used, They reacted 4-50 times stronger than N-glycans (asialo-fetuin and asialo-human al acid GP), The binding of WCA to O-glycans was inhibited by either p-NO2-phenyl alpha,beta GlcNAc or GalNAc. From these results, it is highly possible that cluster (multivalent) effects through the high density of weak inhibitory determinants on glycans, such as GalNAc alpha 1 --> Ser/Thr (Tn), GalNAc at the nonreducing terminal, GlcNAc beta 1 --> at the non-reducing end and/or as an internal residue, play important roles in precipitation, while the GlcNAc beta 1 --> 4GlcNAc disaccharide may play a minor role in the precipitation of mammalian glycan-WGA complexes, (C) 1998 Federation of European Biochemical Societies.