The B4 lectin from Vicia villosa seeds interacts with N-acetylgalactosamine residues alpha-linked to serine or threonine residues in cell surface glycoproteins.
We have examined the carbohydrate binding specificity of the B4 lectin from Vicia villosa seeds. The B4 lectin agglutinates Tn-exposed erythrocytes specifically and binds to these erythrocytes (1.4 X 10(6) sites/cell) with an association constant of 4.2 X 10(7) M-1. The concentrations of saccharides and glycopeptides of defined structure which cause 50% inhibition of B4 lectin binding to Tn-exposed erythrocytes were determined. N-Acetylgalactosamine is the best monosaccharide inhibitor, causing 50% inhibition of binding at a concentration of 0.04 mM. Other monosaccharides inhibit lectin binding in the following order of decreasing potency: N-acetylgalactosamine greater than methyl-alpha-galactopyranoside greater than p-nitrophenyl-alpha- or beta-galactopyranoside greater than methyl-beta-galactopyranoside, galactose greater than galactosamine greater than mannose, N-acetylglucosamine. The disaccharide Gal beta 1,3GalNAc causes 50% inhibition of binding at a concentration of 2.8 mM, a concentration similar to that of the p-nitrophenyl-alpha- or beta-galactopyranosides. Glycopeptides containing O-glycosidically linked oligosaccharide units are significantly more potent inhibitors of lectin binding than the oligosaccharide units alone. The most potent glycopeptide inhibitor is a fetuin glycopeptide containing two alpha-linked N-acetylgalactosamine units. This glycopeptide causes 50% inhibition of lectin binding at a concentration of 0.00034 mM and probably closely resembles the B4 lectin binding site on Tn-exposed erythrocytes.
D000116:Acetylgalactosamine / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D004912:Erythrocytes / Q000378:metabolism; D005688:Galactosamine / Q000031:analogs & derivatives*; D006023:Glycoproteins / Q000378:metabolism*; D006801:Humans; D037102:Lectins / Q000378:metabolism*; D008223:Lymphoma / Q000378:metabolism; D051379:Mice; D037121:Plant Lectins; D012639:Seeds / Q000032:analysis*; D012694:Serine / Q000378:metabolism; D013499:Surface Properties; D013912:Threonine / Q000378:metabolism
D006023:Glycoproteins; D037102:Lectins; D037121:Plant Lectins; D013912:Threonine; D012694:Serine; D005688:Galactosamine; D000116:Acetylgalactosamine