Effects of polyvalency of glycotopes and natural modifications of human blood group ABH/Lewis sugars at the Galβ1-terminated core saccharides on the binding of domain-I of recombinant tandem-repeat-type galectin-4 from rat gastrointestinal tract (G4-N)

In our recent publication, we defined core aspects of the carbohydrate specificity of domain-I of recombinant tandem-repeat-type galectin-4 from rat gastrointestinal tract (G4-N), especially its potent interaction with the linear tetrasaccharide Galβ1-3GlcNAcβ1-3Galβ1-4Glc (Iβ1-3L). The assumed role of galectin-4 as a microvillar raft stabilizer/organizer and as a malignancy-associated factor in hepatocellular and gastrointestinal carcinomas called for further refinement of its binding specificity. Thus, the effects of polyvalency of glycotopes and natural modifications of human blood group ABH/Lewis sugars at the terminal Galβ1-core saccharides were thoroughly examined by the enzyme-linked lectinosorbent and lectin-glycan inhibition assays. The results indicate that (a) a high-density of polyvalent Galβ1-3/4GlcNAc (I/II), Galβ1-3GalNAc (T) and/or GalNAcα1-Ser/ Thr (Tn) strongly favors G4-N/glycoform binding. These glycans were up to 2.3 × 10⁶, 1.4 × 10⁶, 8.8 × 10⁵, and 1.4 × 10⁵ more active than Gal, GalNAc, monomeric I/II and T, respectively; (b) while LFuc is a poor inhibitor, its presence as α1-2 linked to terminal Galβ1-containing oligosaccharides, such as H active Iβ1-3L, markedly enhances the reactivities of these ligands; (c) when blood group A (GalNAcα1-) or B (Galα1-) determinants are attached to terminal Galβ1-3/4GlcNAc (or Glc) oligosaccharides, the reactivities are also increased; (d) with LFucα1-3/4 linked to sub-terminal GlcNAc, the reactivities of these haptens are reduced; and (e) short chain Le ^a/Le^x/Le^y and the short chains of sialyl Le^a/Le^x are poor inhibitors. These distinct binding features of G4-N establish the important concept of affinity enhancement by high density polyvalencies of glycotopes (vs. multi-antennary I/II) and by introduction of an ABH key sugar to Galβ1-terminated core glycotopes. The polyvalent ligand binding properties of G4-N may help our understanding of its crucial role for cell membrane raft stability and provide salient information for the optimal design of blocking substances such as anti-tumoral glycodendrimers.