STUDIES ON LECTINS .75. INTERACTION OF EGG-WHITE GLYCOPROTEINS AND THEIR OLIGOSACCHARIDES WITH THE MONOMER AND THE HEXAMER OF CHICKEN LIVER LECTIN - A MULTIVALENT OLIGOSACCHARIDE-COMBINING SITE EXISTS WITHIN THE CARBOHYDRATE-RECOGNITION DOMAIN

Binding of egg-white glycoproteins and their oligosaccharides to hexameric solubilized form of the chicken hepatic lectin and the monomeric soluble fragment containing the carbohydrate-recognition domain has been investigated by several techniques. Ligand blotting revealed significant differences in binding to two forms of the lectin only for glycoproteins bearing multiple N-linked oligosaccharide moieties in their molecule (riboflavin-binding glycoprotein, avidin or ovomucoid). Inhibition studies indicated that inhibitory potency in a series of linear and branched N-acetyl-D-glucosamine-terminated oligosaccharides is critically dependent on the number and spatial arrangement of the terminal monosaccharide residues for both forms of the lectin. Direct binding of 4-hydroxyphenyl-derivatized radioiodinated oligosaccharides measured by equilibrium dialysis and frontal affinity chromatography points to the existence of two N-acetyl-D-glucosamine-combining sites per one subunit of the lectin, as has been recently reported for the rabbit and rat liver lectin [Lee & Lee (1988) Biochem. Biophys. Res. Commun. 155, 1444-1452]. Highly branch (penta-antennary) oligosaccharides interact with more than one subunit of the hexameric form of the lectin and thus resemble the more complex interaction of the whole glycoprotein.