The specificity of the binding site of Achatinin_H, a sialic acid-binding lectin from Achatina fulica

Abstract

A sialic acid-binding lectin, Achatinin_H (ATN_H), having unique specificity towards 9-O-acetylneuraminic acid, has been purified and characterized. The specificity of this lectin for O-acetylsialic acids was studied in detail, using various sialic acid derivatives and sialoglycoproteins. The potent inhibition of hemagglutination by bovine submaxillary mucin (BSM), which contains 9(7,8)-O-acetylsialic acid and by free 9-O-acetylneuraminic acid confirms the preferential affinity towards this sugar. Further support for the role of O-acetylsialic acid was obtained by sialidase treatment of BSM. O-Deacetylation of the sialic acid residue abolished its inhibitory potency. Moreover, when the trihydroxypropyl side chain of the sialic acid molecule was modified by periodate-borohydride treatment, the truncated C₇-sialic acid was unable to bind ATN_H. This result suggests that the glycerol side chain of Neu5Ac, especially the C-8 and/or C-9 portion is an important determinant for ATN_H. The hemagglutination-inhibition results using several mono-, di-, and tri-saccharides containing terminal sialic acid and various sialoglycoproteins reveals that ATN_H preferentially binds the α-(2 → 6)-linked sialic acid. Furthermore, β-D-GlcNAc-(1 → 3)-[α-NeuGc-(2 → 6)]-GalNAc-ol was found to be the best ligand for ATN_H.