Further characterization of the binding properties of a GalNAc specific lectin from Codium fragile subspecies tomentosoides

Previous study on the binding properties of a lectin isolated from Codium fragile subspecies tomentosoides (CFT) indicates that this lectin recognizes the GalNAcα1→ sequence at both reducing and nonreducing ends. In this study, the carbohydrate specificity of CFT was further characterized by quantitative precipitin (QPA) and inhibition of lectin-enzyme binding assays. Of the glycoforms tested for QPA, all asialo-GalNAcα 1/2 [ containing glycoproteins reacted well with the lectin. Asialo hamster and ovine submandibular glycoproteins, which contain almost exclusively Tn (GalNAcα12[Ser/Thr) residues as carbohydrate side chains, and Streptococcus type C polysaccharide completely precipitated the lectin added, while the GalNAcβ1→containing Tamm-Horsfall Sd(a⁺) glycoprotein and its asialo product were inactive. Among the oligosaccharides tested for inhibiting lectin-glycoprotein interaction, GalNAcα1→3GalNAcβ1→3Galα1→4Galβ1→ 4Glc(Fp) and Galβ1→3GalNAcα1→benzyl (Tα) were the best, and about 125- fold more active than GalNAc. They were about 3.3, 6.6, and 43 times more active than Tn containing glycopeptides, GalNAcα1→3(LFucα1→ 2)Gal(A(h)) and Galβ1→3GalNAc(T), respectively. From the present and previous results, it is concluded that the combining site of CFT is probably of a groove type that recognizes from GalNAcα1→ to pentasaccharide(Fp). The carbohydrate specificity of this lectin can be constructed and summarized in decreasing order by lectin determinants as follows: Fp and Tα > Tn cluster > A(h)>> I/II.