Five alpha-D-galactopyranosyl-binding isolectins from Bandeiraea simplicifolia seeds

The role of lectins in blood group serology

Many lectins display blood group activity, and extracts from Dolichos biflorus (anti-A1), Ulex europaeus (anti-H), and Vicia graminea (anti-N) seeds provide an alternative to human sera as a source of blood-typing reagents. However, the major application of lectins in blood group serology undoubtedly lies in the recognition and elucidation of red celll polyagglutination. In this respect, lectins from Arachis hypogaea (anti-T/Tk), Salvia sclarea (anti-Tn). Salvia horminum (anti-Tn + Cad). Dolichos biflorus (anti-Tn/Cad) Glycine max, and the N-acetyl-D-glucosminyl-binding lectin, BS II (anti-Tk) from Bandeiraea simplicifolia seeds, provide an invaluable source of reagents for use in investigative immunohemotology. Because of their specific carbohydrate-binding properties, lectins have also been used as probes in studies on the topography of the red cell surface. This latter appliction has provided much information on the structure of the MN, T, and Tn red cell surface receptors and has aided in defining the red cell membrane abnormalities associated with certain uncommon phenotypes within the MN blood group system.

A study of the specificity of Bandeiraea simplicifolia lectin I by competitive-binding assay with blood-group substances and with blood-group A and B active and other oligosaccharides

The specificity of Bandeiraea simplicifolia lectin I (BS I) has been studied by competitive-binding assays (CBA) using tritium-labeled human B and hog A substances. Blood-group B substances isolated from horse gastric mucosae and from human ovarian-cyst fluids were much better inhibitors of binding of tritiated blood-group B substance to insoluble BS I-Sepharose 2B than were human blood-group A substances from saliva and ovarian-cyst fluid. A and B active blood-group substances showed the same range of potency in inhibiting binding of tritium-labeled hog A substance to BS I-Sepharose 2B. CBA with BS I-Sepharose 2B, labeled human blood-group B substance, and human blood-group A and B active aligosaccharides separated the haptens into two groups differing in slope. Group 1, containing methyl alpha-D-GalNAcp, D-GalNAcp, and an A active pentasaccharide ARL 0.52, with 3, 19, and 25 nmol respectively needed for 50% inhibition of binding, has a lower slope than group 2, which contains alpha-D-GalNAcp-(1 leads to 3)-2-acetamido-2-deoxy-D-galactitol and p-nitrophenyl alpha-D-GalNAcp, with 3 nmol of each required for 50% inhibition of binding, as well as ten glycosides with terminal, nonreducing, alpha-linked D-Galp. The most potent inhibitors of this group were p-nitrophenyl alpha-D-Galp, alpha-D-Galp-(1 leads to 3)-D-Galp, alpha-D-Galp-(1 leads to 6)-D-Glcp, and methyl alpha-D-Galp, with 5, 7.4, 9.6, and 11 nmol respectively needed to inhibit binding by 50%. The difference in slopes was explainable in terms of a recent finding that BS I exists as a mixture of five isolectins composed of two subunits having different specificities; subunit A is most specific for alpha-linked, terminal, nonreducing D-GalNAcp, but it also reacts with alpha-linked, terminal, nonreducing D-Galp, whereas subunit B tends to be more specific for terminal, nonreducing, alpha-linked D-Galp.