Recognition profile of Bauhinia purpurea agglutinin (BPA)

Bauhinia purpurea agglutinin (BPA) is a Galβ1-3GalNAc (T) specific leguminous lectin that has been widely used in multifarious cytochemical and immunological studies of cells and tissues under pathological or malignant conditions. Despite these diverse applications, knowledge of its carbohydrate specificity was mainly limited to molecular or submolecular T disaccharides. Thus, the requirement of high density polyvalent or multi-antennary carbohydrate structural units for BPA binding and an updated affinity profile were further evaluated by enzyme-linked lectinosorbent (ELLSA) and inhibition assays. Among the glycoproteins (gps) tested and expressed as 50% nanogram inhibition, the high density polyvalent GalNAcα1-Ser/Thr (Tn) and Galβ1-3/4GlcNAc (I/II) glycotopes present on macromolecules generated a great enhancement of binding affinity for BPA as compared to their monomers. The most potent inhibitors were a Tn-containing gp (asialo OSM) and a I/II containing gp (human blood group precursor gp), which were up to 1.7 × 10⁴ and 2.3 × 10³ times more potent than monovalent Gal and GalNAc, respectively. However, multi-antennary glycopeptides, such as tri-antennary Galβ1-4GlcNAc, which was slightly more active than II or Gal, gave only a minor contribution. Regarding the carbohydrate structural units studied by the inhibition assay, blood group GalNAcβ1-3/4Gal (P/S) active glycotopes were active ligands. The overall binding profile of BPA was: high density polyvalent T/Tn and II clusters ≫> Tn-glycopeptides (M.W. <3.0 × 10³)/Tα monomer > monovalent P/S > Tn monomer and GalNAc > tri-antennary II > Gal ≫ Man and Glc (inactive). These findings give evidence for the binding of this lectin to dense cell surface T, Tn and I/II glycoconjugates and should facilitate future usage of this lectin in biotechnological and medical applications.