Further characterization of the saccharide specificity of snake gourd (Trichosanthes anguina) seed lectin

Abstract

The galactose-specific lectin present in the seeds of Trichosanthes anguina (snake gourd) has been further characterized by isoelectrofocusing experiments to identify the number of isolections. Its carbohydrate-binding specificity has also been characterized in greater detail by the haemagglutination-inhibition technique using several mono-, di- and oligosaccharides. The results suggest that affinity purified snake gourd seed lectin (SGSL) is made up of a single isolectin with a pI of 5.0. The lectin exhibits a strong preference for the β-anomer of galactose over the α-anomer and ligands with a hydrophobic moiety attached to the β-anomer of galactose such as p-nitrophenyl-β-D-galactopyranoside and 4-methylumbelliferyl-β-D-galactopyranoside, inhibit the lectin activity better than the simple methyl glycosides of galactose, suggesting that additional hydrophobic interactions stabilize the binding of these ligands bearing nonpolar moieties. The disaccharides lactulose and thiodigalactoside exhibit considerably higher affinity than lactose and MeβGal, indicating that their reducing sugar moieties may have additional favourable interactions with the lectin combining site.