The N-terminal carbohydrate recognition domain of galectin-8 recognizes specific glycosphingolipids with high affinity

Abstract

Galectin-8 is a member of the galectin family and has two tandem repeated carbohydrate recognition domains (CRDs). We determined the binding specificities of galectin-8 and its two CRDs for oligosaccharides and glycosphingolipids using ELISA and surface plasmon resonance assays. Galectin-8 had much higher affinity for 3′-O-sulfated or 3′-O-sialylated lactose and a Lewis x–containing glycan than for oligosaccharides terminating in Galβ1→3/4GlcNAc. This specificity was mainly attributed to the N-terminal CRD (N-domain), whereas the C-terminal CRD (C-domain) had only weak affinity for a blood group A glycan. The N-domain bound not only to oligosaccharides but also to glycosphingolipids including sulfatide (SM4 s), SM3, sialyl Lc4Cer, SB1a, GD1a, GM3, and sialyl nLc4Cer, suggesting that the N-domain recognizes a 3-O-sulfated or 3-O-sialylated Gal residue. The substitution of the C-3 of the Gal residue in lactose or N-acetyllactosamine with sulfate increased the degree of recognition by galectin-8 more potently than substitution with sialic acid. This is the first demonstration that galectin-8 binds to specific sulfated or sialylated glycosphingolipids with high affinity (K_D∼10⁻⁸–10⁻⁹ M). When the Gln⁴⁷ residue of the N-domain was converted to Ala⁴⁷, the specific affinity for sulfated or sialylated glycans was selectively lost, indicating that this Gln⁴⁷ plays important roles for binding to Neu5Acα2→3Gal or SO₃⁻→3Gal residues. The binding ability of galectin-8 to membrane-associated GM3 was confirmed using CHO cells, which predominantly express GM3. Binding of CHO cells to the mutein was significantly lower than to the N-domain.