Differential affinities of Erythrina cristagalli lectin (ECL) toward monosaccharides and polyvalent mammalian structural units

Previous studies on the carbohydrate specificities of Erythrina cristagalli lectin (ECL) were mainly limited to analyzing the binding of oligo-antennary Galβ1→4GlcNAc (II). In this report, a wider range of recognition factors of ECL toward known mammalian ligands and glycans were examined by enzyme-linked lectinosorbent and inhibition assays, using natural polyvalent glycotopes, and a glycan array assay. From the results, it is shown that GalNAc was an active ligand, but its polyvalent structural units, in contrast to those of Gal, were poor inhibitors. Among soluble natural glycans tested for 50% molecular mass inhibition, Streptococcus pneumoniae type 14 capsular polysaccharide of polyvalent II was the most potent inhibitor; it was 2.1×10⁴, 3.9×10³ and 2.4×10³ more active than Gal, tri-antennary II and monomeric II, respectively. Most type II-containing glycoproteins were also potent inhibitors, indicating that special polyvalent II and Galβ1-related structures play critically important roles in lectin binding. Mapping all information available, it can be concluded that: [a] Galβ1→4GlcNAc (II) and some Galβ1-related oligosaccharides, rather than GalNAc-related oligosaccharides, are the core structures for lectin binding; [b] their polyvalent II forms within macromolecules are a potent recognition force for ECL, while II monomer and oligo-antennary II forms play only a limited role in binding; [c] the shape of the lectin binding domains may correspond to a cavity type with Galβ1→4GlcNAc as the core binding site with additional one to four sugars subsites, and is most complementary to a linear trisaccharide, Galβ1→4GlcNAcβ1→6Gal. These analyses should facilitate the understanding of the binding function of ECL.