Comparison of the carbohydrate‐binding specificities of seven N‐acetyl‐D‐galactosamine‐recognizing lectins

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Abstract
Seven plant lectins, Dolichos biflorus agglutinin (DBA), Griffonia simplicifolia agglutinin (GSA, isolectin A4), Helix pomatia agglutinin (HPA), soybean (Glycine max) agglutinin (SBA), Salvia sclarea agglutinin (SSA), Vicia villosa agglutinin (VVA, isolectin B4) and Wistaria floribunda agglutinin (WFA), known to be specific for N‐acetyl‐D‐galactosamine‐(GalNAc) bearing glycoconjugates, have been compared by the binding of their radiolabelled derivatives, to eight well‐characterized synthetic oligosaccharides immobilized via a spacer on an inert silica matrix (Synsorb). The eight oligosaccharides included the Forssman, the blood group A and the T antigens, as well as αGalNAc coupled directly to the support (Tn antigen) and also structures with GalNAc linked α or β to positions 3 or 4 of an unsubstituted Gal. The binding studies clearly distinguished the lectins into αGalNAc‐specific agglutinins like DBA, GSA and SSA, and lectins which recognize α‐ as well as β‐linked GalNAc residues like HPA, VVA, WFA and SBA. HPA was the only lectin which bound to the βGall → 3αGalNAc‐Synsorb adsorbent (T antigen) indicating that it also recognizes internal GalNAc residues. Among the αGalNAc‐specific lectins, DBA strongly recognized blood group A structures while GSA displayed weaker recognition, and SSA bound only slightly to this affinity matrix. In addition, DBA and SSA were able to distinguish between GalNAc linked α1 → 3 and GalNAc linked α1 → 4, to the support, the latter being a much weaker ligand. These results were corroborated by the binding of the lectins to biological substrates as determined by their hemagglutination titers with native and enzyme‐treated red blood cells carrying known GalNAc determinants, e.g. blood group A, and the Cad and Tn antigens. For SSA, the binding to the αGalNAc matrix was inhibited by a number of glycopeptides and glycoproteins confirming the strong preference of this lectin for αGalNAc‐Ser/ Thr‐bearing glycoproteins.