Carbohydrate binding specificity of the B-cell maturation mitogen from Artocarpus integrifolia seeds

Artocarpin, a mannose-specific lectin, is a homotetrameric protein (Mr 65,000) devoid of covalently attached carbohydrates and consists of four isolectins with pI in the range 5-6.5. Investigations of its carbohydrate binding specificity reveal that among monosaccharides, mannose is preferred over glucose. Among mannooligosaccharides, mannotriose (Manα1-3[Manα1-6]Man) and mannopentaose are the strongest ligands followed by Manα1-3Man. Extension of these ligands by GlcNAc at the reducing ends of mannooligosaccharides tested remarkably improves their inhibitory potencies, while substitution of both the α1-3 and α1-6 mannosyl residues of mannotriose and the core pentasaccharide of N-linked glycans (Manα1-3[Manα1-6]Manβ1-4GlcNAcβ1-4GlcNAc) by GlcNAc or N-acetyllactosamine in β1-2 linkage diminishes their inhibitory potencies. Sialylated oligosaccharides are non-inhibitory. Moreover, the substitution of either α1-3 or α1-6 linked mannosyl residues of M5Gn or both by mannose in α1-2 linkage leads to a considerable reduction of their inhibitory power. Addition of a xylose residue in β1-2 linkage to the core pentasaccharide improves the inhibitory activity. Considering the fact that artocarpin has the strongest affinity for the xylose containing hepasaccharide from horseradish peroxidase, which differs significantly from all the mannose/glucose-specific lectins, it should prove a useful tool for the isolation and characterization of glycoproteins displaying such structure