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 lect in, abrin A, from the seeds of Abrus precatorius for mammalian carbohydrate ligands, was studied by enzyme linked lectinosorbent assay and by inhibiti on of abrin A-glycan interaction. From the results, it is concluded that: ( 1) abrin A reacted well with Gal beta1 --> 4GlcNAc (II), Gal alpha1 --> 4Ga l (E), and Gal beta1 --> 3GalNAc (T) containing glycoproteins. But it react ed weakly with sialylated gps and human blood group A,B,H active glycoprote ins (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 s pecific configuration at C-3, C-4, and deoxy C-6 of the (D)Fuc pyranose rin g to penta-saccharides and probably internal Gal alpha,beta -->; and (3) it s binding affinity toward mammalian structural features can be ranked in de creasing order as follows: cluster forms of II, T, B/E (Gal alpha1 -->3/4Ga l) > monomeric T > monomeric H > monomeric B/E, Gal > GalNAc > monomeric I much greater than Man and Glc (inactive). These active glycotopes can be us ed to explain the possible structural requirements for abrin A toxin attach ment. (C) 2001 Elsevier Science Inc. All rights reserved.