The interaction of wheat germ agglutinin with sialoglycoproteins. The role of sialic acid.

The role of sialic acid in the interaction of sialoglycoproteins with wheat germ agglutinin was investigated by using several well characterized saccharides and sialoglycoconjugates. N-Acetylneuraminic acid and neuramin 2 + 3 lactose, in addition to N-acetyl-Dglucosamine and its fil-+ 4 oligomers were found to be inhibitors of wheat germ agglutinin-induced hemagglutination. Neuraminic acid-/?-methyl ketoside, N-glycolylneuraminic acid and several other acidic sugars were noninhibitors. Both glycophorin and al-acid glycoprotein were excellent inhibitors, whereas the corresponding asialo compounds were either very poor or noninhibitors. Among the mucins tested, all except porcine submaxillary mucin, which has N-glycolylneuraminic acid, were potent inhibitors. The results of double diffusion experiments, in which the ability of the glycoconjugates to form precipitin line with wheat germ agglutinin was tested, were in agreement with the agglutination inhibition data. Affinity chromatography of labeled glycoconjugates on wheat germ agglutinin-Sepharose 4B columns confirmed that N-acetylneuraminyl residues play an important role in the binding of sialoglycoconjugates to this lectin. The results suggest that the binding of a glycoprotein to a wheat germ agglutinin-Sepharose 4B column may be influenced both by the density of the binding sugar residues (N-acetyl-D-glucosamine and Nacetylneuraminic acid) on the glycoprotein and by the density of the lectin molecules on the gel beads. In cell affinity chromatography, the cells interacted irreversibly with wheat germ agglutinin-Sepharose 6MB beads; this binding was partially lost on treatment of the cells with neuraminidase. Models for the interaction of wheat germ agglutinin with N-acetylneuraminic acid and polysialoglycoconjugates are presented. Wheat germ agglutinin is also able to interact with glycoproteins containing multiple nonreducing terminals of N-acetylgalactosamine as are present, for example, in asialo ovine and bovine submaxillary mucins.