Background: Erythrina corallodendron lectin (ECorL) is one of the potent applied lectins. In previous studies, the carbohydrate specificities of this lectin were limited to monosaccharides, simple oligosaccharides and several clusters. However, the polyvalent factor has not been investigated.
Methods: The binding properties at the combining sites of ECorL were characterized by sensitive enzyme-linked lectinosorbent (ELLSA) and inhibition assays, using our collection of ligands and polyvalent natural glycans with known glycotopes.
Results: Results of both binding and inhibition assays revealed a very high affinity between ECorL and Galbeta1-4GlcNAc (II)-containing glycoproteins. Among soluble natural glycans tested for inhibition, the high-density polyvalent II glycotopes, such as Streptococcus pneumoniae type 14 capsular polysaccharide which is composed of repeating poly-II residues, resulted in 2.4 x 10(4), 1.4 x 10(3) and 8.6 x 10(2)-fold higher affinities to ECorL than the monomeric Gal, linear II and tri-antennary II, respectively, at the non-reducing end in N-linked glycopeptides (Tri-II). The ECorL-glycan interaction was also strongly inhibited by most of the other high-density II-containing glycoproteins. Although GalNAc was as potent an inhibitor as Gal, its polyvalent structural units were poor inhibitors.
Conclusions:  Galbeta1-4GlcNAc (II) and other Galbeta1 -related oligosaccharides are essential for binding.  Their polyvalent form in glycoproteins is the most important binding factor for ECorL, while II monomer and oligo-antennary II forms play only a limited role in binding.  Although GalNAc is more active than Gal for ECorL, its reactivity is not changed by polyvalent effects. This lectin may be used as a tool to study glycobiology in basic and medical sciences.