We examined the specificity of
limulin,
Limax flavus agglutinin (LFA) and
Sambucus nigra agglutinin I (SNA I) at the submolecular level of
sialic acid, and characterized their interactions with a panel of structurally distinct
sialoglycoproteins. In haemagglutination inhibition assays NeuAc-alpha-
glycosides were stronger inhibitors for
limulin and LFA than native
N-acetylneuraminic acid (NeuAc). The N-acetyl of NeuAc was crucial for binding to both
lectins. N-thioacetylated NeuAc lost affinity for LFA, but still bound to
limulin. Thus, distinct intermolecular interactions are involved in binding of
sialic acid to the
lectins. The glyceryl side chain was required for interaction with LFA, but not with
limulin. SNA I specifically bound NeuAc alpha 2 --> 6Gal beta 1 --> 4Glc, but not monomeric
sialic acids.
Limulin and LFA strongly interacted with O-chain
glycoproteins, whereas SNA I preferred N-chain
proteins that carry NeuAc alpha 2 --> 6 residues. The
lectins were compared with those from Cepaea hortensis and Tachypleus tridentatus (TTA) and to
wheat-germ agglutinin, and were then used to probe tumour cell lines for cell surface sialylation. With the exception of TTA, all
lectins interacted with the tumour cells.
Limulin distinguished between the low (Eb) and highly (ESb) metastatic mouse
lymphoma lines by selectively agglutinating
sialidase-treated ESb cells.