Pathogenesis of Shigella Diarrhea: Evidence for an N-Linked Glycoprotein Shigella Toxin Receptor and Receptor Modulation by -Galactosidase

Abstract

Pathogenic mechanisms in infectious diseases often involve specific receptor-ligand interactions of cells and soluble molecules. To further elucidate structure-function relations for shigella toxin receptors, we studied binding of purified ¹²⁵I-labeled toxin and biologic response under various conditions in an experimental model using HeLa cells. Response to toxin was reversibly inhibited by treatment of cells with trypsin or tunicamycin, an inhibitor of glycoprotein synthesis that also significantly inhibited toxin binding, a result indicating that the receptor is an N-linked glycoprotein. Removal of terminal β-linked galactose from the HeLa cell surface with β-galactosidase increased toxin binding and activity, and it also potentiated the effects of lysozyme and wheat-germ agglutinin, which recognize oligomeric β1→-linked N-acetyl-d-glucosamine and inhibit toxin activity as well. Incubation of cells with β-N-acetylglucosaminidase, which cleaves terminal β-linked N-acetyl-d-glucosamine, inhibited toxin activity. Effects of β-galactosidase were reversed by readdition of galactose to cell-surface oligosaccharide acceptors. The data demonstrate that alterations of a single sugar on cell-surface glycoproteins may have a dramatic effect on receptor activity and indicate that shigella toxin is a sugar-binding protein with specificity for β1→4-linked N-acetyl-d-glucosamine.