Novel interactions of complex carbohydrates with peanut (PNA), Ricinus communis (RCA-I), Sambucus nigra (SNA-I) and wheat germ (WGA) agglutinins as revealed by the binding specificities of these lectins towards mucin core-2 O-linked and N-linked glycans and related structures

Plant lectins through their multivalent quaternary structures bind intrinsically flexible oligosaccharides. They recognize fine structural differences in carbohydrates and interact with different sequences in mucin core 2 or complex-type N-glycan chain and also in healthy and malignant tissues. They are used in characterizing cellular and extracellular glycoconjugates modified in pathological processes. We study here, the complex carbohydrate-lectin interactions by determining the effects of substituents in mucin core 2 tetrasaccharide Gal beta 1-4GlcNAc beta 1-6(Gal beta 1-3) GalNAc alpha-O-R and fetuin glycopeptides on their binding to agarose-immobilized lectins PNA, RCA-I, SNA-I and WGA. Briefly, in mucin core 2 tetrasaccharide (i) structures modified by alpha 2-3/6-Sialyl LacNAc, LewisX and alpha 1-3-Galactosyl LacNAc resulted in regular binding to PNA whereas compounds with 6-sulfo LacNAc displayed no-binding; (ii) strucures bearing alpha 2-6-sialyl 6-sulfo LacNAc, or 6-sialyl LacdiNAc carbohydrates displayed strong binding to SNA-I; (iii) structures with alpha 2-3/6-sialyl, alpha 1-3Gal LacNAc or LewisX were non-binder to RCA-I and compounds with 6sulfo LacNAc only displayed weak binding; (iv) structures containing LewisX, 6-Sulfo LewisX, alpha 2-3/6-sialyl LacNAc, alpha 2-3/6-sialyl 6-sulfo LacNAc and GalNAc Lewis-a were non-binding to WGA, those with alpha 1-2Fucosyl, alpha 1-3-Galactosyl LacNAc, alpha 2-3-sialyl T-hapten plus 3'/6' sulfo LacNAc displayed weak binding, and compounds with alpha 2-3-sialyl T-hapten, alpha 2.6-Sialyl LacdiNAc, alpha 2-3-sialyl D-Fuc beta 1-3 GalNAc and Fuca-1-2 D-Fuc beta-1-3GalNAc displaying regular binding and GalNAc LewisX and LacdiNAc plus D-Fuc beta-1-3 GalNAc alpha resulting in tight binding. RCA-I binds Fetuin triantennary asialoglycopeptide 100 % after alpha-2-3 and 25% after alpha-2-6 sialylation, 30% after alpha-1-2 and 100% after alpha-1-3 fucosylation, and 50% after alpha-1-3 galactosylation. WGA binds 3-but not 6-Fucosyl chitobiose core. Thus, information on the influence of complex carbohydrate chain constituents on lectin binding is apparently essential for the potential application of lectins in glycoconjugate research.