Carbohydrate specificity of a toxic lectin, abrin A, from the seeds of Abrus precatorius (jequirity bean)

To elucidate of the mechanism of intoxication, the affinity of a toxic lectin, abrin A, from the seeds of Abrus precatorius for mammalian carbohydrate ligands, was studied by enzyme linked lectinosorbent assay and by inhibition of abrin A-glycan interaction. From the results, it is concluded that: (1) abrin A reacted well with Galβ1→4GlcNAc (II), Galα1→4Gal (E), and Galβ1→3GalNAc (T) containing glycoproteins. But it reacted weakly with sialylated gps and human blood group A,B,H active glycoproteins (gps); (2) the combining site of abrin A lectin should be of a shallow groove type as this lectin is able to recognize from monosaccharides with specific configuration at C-3, C-4, and deoxy C-6 of the _DFuc pyranose ring to penta-saccharides and probably internal Galα,β→; and (3) its binding affinity toward mammalian structural features can be ranked in decreasing order as follows: cluster forms of II, T, B/E (Galα1→3/4Gal) > monomeric T > monomeric II > monomeric B/E, Gal > GalNAc > monomeric I ≫ Man and Glc (inactive). These active glycotopes can be used to explain the possible structural requirements for abrin A toxin attachment.