Binding characteristics of N-acetylglucosamine-specific lectin of the isolated chicken hepatocytes: similarities to mammalian hepatic galactose/N-acetylgalactosamine-specific lectin

Abstract

Binding characteristics of N-acetylglucosamine-(GlcNAc) specific lectin on the chicken hepatocyte surface were probed by an inhibition assay using various sugars and glycosides as inhibitors. Results indicated that the binding area of the lectin is small, interacting only with GlcNAc residues whose 3-and 4-OH''s are open. The combining site is probably of through-type, since substitution with as large a group as monosaccharide is permitted on the C-6 side of GlcNAc, and on the C-1 side, the aglycon of GlcNAc can be very large (e.g., a glycoprotein). These binding characteristics are shared with the homologous mammalian lectin specific for galactose/N-acetylgalactosamine, suggesting that tertiary structure of the combining area of these two lectins is similar. This is understandable, since there is .apprx. 40% amino acid sequence identitity in the carbohydrate recognition domain of these two lectins [Drickamer, K., Mannon, J. F., Binns, G., and Leung, J. O. (1984) J. Biol. Chem. 259, 770-778]. A series of glycosides, each containing two GlcNAc residues separated by different distances (from 0.8 to 4.7 nm), were synthesized. Inhibition assay with these and other cluster glycosides indicated that clustering of two or more GlcNAc residues increased the affinity toward the chicken lectin tremendously. Among the ligands containing two GlcNAc1 resisues, the structure which allows a maximal inter-GlcNAc distance of 3.3 nm had the stronges affinity, its affinity increase over GlcNAc (monosaccharide) amounting to 100-fold. Longer distances slightly diminished the affinity, while shortening the distance caused substantial decrease in the affinity. Inhibition studies with reduced oligosaccharides and glycopeptides with multiterminal GlcNAc residues indicated that there is a no increase in affinity at all when two GlcNAc residues are separated in space only by 0.8 nm. These results suggest that spatial arrangements of combining sites of the chicken and mammalian lectins are also quite similar.