Binding of synthetic oligosaccharides to the hepatic Gal/GalNAc lectin. Dependence on fine structural features.

Y C Lee,M R Hardy,R R Townsend,H Lönn,J Lönngren,M Haraldsson,J Arnarp

doi:10.1016/s0021-9258(18)33240-x

Abstract

A series of synthetic oligosaccharides, resembling natural N-acetyllactosamine type glycans, were tested for their ability to inhibit the binding of labeled ligand to the mammalian hepatic lectin on rabbit hepatocytes at 2 degrees C. A dramatic hierarchy of inhibitory potency (tetraantennary greater than triantennary much greater than biantennary much greater than monoantennary) could be demonstrated. The range of concentration required for 50% inhibition of labeled ligand binding extended from approximately 1 mM, for the monoantennary oligosaccharides, to approximately 1 nM for triantennary oligosaccharides, even though the absolute Gal concentration increased only 3-fold. It was found that the number of Gal residues/cluster and their branching mode are major determinants of binding affinity of ligands to the hepatic lectin on the surface of hepatocytes.

Highlights

From the +Departmentof Biology and The McCoZZum-Pratt Institute, The Johns HopkinsUniversity, Baltimore, Maryland 21218, the IDepartmentof Medicine, Division of Hematology, The Johns HopkinsUniversity, School ofMedicine, Baltimore, Maryland21205, and the #Department of Organic Chemistry, Arrhenius Laboratory, Lrniuersity of Stockholm, S-106 91 Stockholm, Sweden
A series of synthetic oligosaccharides, resembling Since the “cluster effecotf”Gal residues was demonstrated natural N-acetyllactosamine type glycans, were tested more distinctly with intact hepatic parenchymal cells [1, 2], for their ability to inhibit the binding of labeled ligand inhibition of ligand bindingto isolated rabbit hepatocyteswas to the mammalian hepatic lectin on rabbit hepatocytes studied
Timated from the concentration of ligand required for 50% inhibition of binding ([I~Ro,f)“‘I-Tyr-asialotriantennary glycopeptide to rabbit hepatocytesat 2 “C. Inhibitory potencyof the oligosaccharides was in the expected order of tetraantennary > triantennary > biantennary > monoantennary, and the effect of “clustering” was clearly demonstrated

Summary

DEPENDENCE ON FINE STRUCTURAL FEATURES*

A dramatic hierarchy of inhibitory potency (tetraantennary> triantennary >> biantennary >> monoantennary) could be demonstrated. The range of concentration required for 50%inhibition of labeled ligand binding extended from -1 m,for the monoantennary oligosaccharides, to -1 n~ for triantennary oligosaccharides, even though the absolute Gal concentration increased only 3-fold. Itwas found that the number of Gal residues/cluster and their branching modeare major determinants of binding affinity of ligands to the hepatic lectin on the surface of hepatocytes. Inhibitory potencyof the oligosaccharides was in the expected order of tetraantennary > triantennary > biantennary > monoantennary, and the effect of “clustering” was clearly demonstrated. Ln addition, within each group of the oligosaccharides, subtle changes in structural features (such as positions of branching) exerted great influence on the relative binding affinity. It has been shown that the hepaticlectin on the surfaceof mammalian hepatocytes caneffectively discriminate between clusters of 1, 2, and 3 galactose‘residues. Thishasbeen

EXPERIMENTAL PROCEDURES

Gal Gal

RESULTS AND DISCUSSION

The monoantennary ligand used was