THE SPECIFICITY OF THE BINDING-SITE OF ACHATININ(H), A SIALIC ACID-BINDING LECTIN FROM ACHATINA-FULICA

A sialic acid-binding lectin, Achatinin(H) (ATN(H)), having unique spe cificity towards 9-O-acetylneuraminic acid, has been purified and char acterized. The specificity of this lectin for O-acetylsialic acids was studied in detail, using various sialic acid derivatives and sialogly coproteins. The potent inhibition of hemagglutination by bovine submax illary mucin (BSM), which contains 9(7,8)-O-acetylsialic acid and by f ree 9-O-acetylneuraminic acid confirms the preferential affinity towar ds 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 tri hydroxypropyl side chain of the sialic acid molecule was modified by p eriodate-borohydride treatment, the truncated C-7-sialic acid was unab le to bind ATN(H). This result suggests that the glycerol side chain o f Neu5Ac, especially the C-8 and/or C-9 portion is an important determ inant for ATN(H). The hemagglutination-inhibition results using severa l mono-, di-, and tri-saccharides containing terminal sialic acid and various sialoglycoproteins reveals that ATN(H) preferentially binds th e (alpha-(2 --> 6)-linked sialic acid. Furthermore, beta-D-GlcNAc-(1 - -> 3)-[alpha-NeuGc-(2 --> 6)]-GalNAc-ol was found to be the best ligan d for ATN(H).