Forssman pentasaccharide and polyvalent Galβ1 → 4GlcNAc as major ligands with affinity for Caragana arborescens agglutinin

The binding properties of Caragana arborescens agglutinin (CAA, pea tree agglutinin) were studied by enzyme linked lectinosorbent assay (ELLSA) and by inhibition of CAA-glycan interaction. Among glycoproteins (gps) tested, CAA reacted strongly with asialo bird nest gp, asialo rat sublingual gp, human Tamm-Horsfall Sd(a⁺) urinary gp (THGP) and asialo THGP that are rich in GalNAcα1→, GalNAcβ1→ and/or Galβ1→4GlcNAc residues. CAA also bound tightly with multi-valent Galβ1→4GlcNAc (mII) containing glycoproteins (human blood group precursor gps, asialo fetuin) and asialo ovine salivary glycoprotein (Tn, GalNAcα1→Ser/Thr), but CAA reacted poorly or not at all with sialylated glycoproteins tested. Of the sugars tested for inhibition of binding, Forssman pentasaccharide (F(p), GalNAcα1→3GalNAcβ1→3Galα1→4Galβ1→4Glc) was the best. It was about 2.3, 9.5 and 52.6 times more active than Galβ1→4GlcNAc, GalNAc and Gal, respectively, and about 1.9 times more active than tri-antennary Galβ1→4GlcNAc (Tri-II). These results suggest that this agglutinin is mainly specific for F(p), mII and Tn clusters. This property can be used to detect human abnormal glycotopes related to F(p) and unmasked mII/Tn clusters and to study cell growth and differentiation given the lack of toxicity of this lectin toward mouse fibroblast cells.