Chemical synthesis of globotriose and galabiose: relative stabilities of their complexes with Escherichia coli Shiga-like toxin-1 as determined by denaturation-titration with guanidinium chloride

Abstract

Globotriose [α-D-Gal-(1→4)-β-D-Gal-(1→4)-D-Glc] is the carbohydrate moiety of the globotriosyl ceramide (Gb₃), also known as the germinal centre B-cell differentiation antigen CD77, a glycolipid present on the plasma membrane of certain mammalian cells. In Gb₃, globotriose functions as the cell-surface receptor for Shiga toxin and for the Shiga-like toxins (verocytotoxins). Here we report the chemical synthesis of globotriose and the corresponding terminal disaccharide, galabiose [α-D-Gal-(1→4)-β-D-Gal]. Globotriose and galabiose are attached via a linker to CNBr-activated Sepharose to generate affinity matrices that permit the one-step purification of recombinant Shiga-like toxin-1 from crude E. coli homogenates. Toxin is released from either of the immobilised saccharides by elution with 6 M guanidinium chloride. After dilution of the denaturant, the released toxin had full catalytic activity. Denaturation-titration experiments show that the bound toxin is released from galabiose-Sepharose at 2.3 M guanidinium chloride, while its release from globotriose-Sepharose requires a higher concentration of 4.8 M. These results indicate that the glucose component of globotriose contributes ≈2.6 kcal mol^–1 to the binding energy relative to galabiose.