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

Abstract

Previous study on the binding properties of a lectin isolated from Codium fragile subspecies tomentosoides (CFT) indicates that this lectin recognizes the GalNAc alpha1--> 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-GalNAc alpha1--> containing glycoproteins reacted well with the lectin. Asialo hamster and ovine submandibular glycoproteins, which contain almost exclusively Tn (GalNAc alpha1-->Ser/Thr) residues as carbohydrate side chains, and Streptococcus type C polysaccharide completely precipitated the lectin added, while the GalNAc beta1-->containing Tamm-Horsfall Sd(a+) glycoprotein and its asialo product were inactive. Among the oligosaccharides tested for inhibiting lectin-glycoprotein interaction, GalNAc alpha1-->3GalNAc beta1-->3Gal alpha1-->4Gal beta1--> 4Glc(Fp) and Gal beta1-->3GalNAc alpha1-->benzyl (T alpha) 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, GalNAc alpha1-->3(LFuc alpha1--> 2)Gal(Ah) and Gal beta1-->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 GalNAc alpha1--> to pentasaccharide(Fp). The carbohydrate specificity of this lectin can be constructed and summarized in decreasing order by lectin determinants as follows: Fp and T alpha > Tn cluster > Ah >> I/II.