Clostridium botulinum type A haemagglutinin-positive progenitor toxin (HA+-PTX) binds to oligosaccharides containing Galβ1-4GlcNAc through one subcomponent of haemagglutinin (HA1)

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Abstract
Haemagglutinin (HA) activity of Clostridium botulinum type A 19S and 16S toxins (HA-positive progenitor toxin; HA+-PTX) was characterized. HA titres against human erythrocytes of HA+-PTX were inhibited by the addition of lactose, D-galactose, N-acetyl-D-galactosamine and D-fucose to the reaction mixtures. A direct glycolipid binding test demonstrated that type A HA+-PTX strongly bound to paragloboside and some neutral glycolipids, but did not bind to gangliosides. Type A HA+-PTX also bound to asialoglycoproteins (asialofetuin, neuraminidase-treated transferrin), but not to sialoglycoproteins (fetuin, transferrin). Although glycopeptidase F treatment of asialofetuin abolished the binding of HA+-PTX, endo-α-N-acetylgalactosaminidase treatment did not. Thus these results can be interpreted as indicating that type A HA+-PTX detects and binds to Galβ1-4GlcNAc in paragloboside and the N-linked oligosaccharides of glycoproteins. Regardless of neuraminidase treatment, type A HA+-PTX bound to glycophorin A which is a major sialoglycoprotein on the surface of erythrocytes. Both native glycophorin A and neuraminidase-treated glycophorin A inhibited the binding of erythrocytes to type A HA+-PTX. Since the N-linked oligosaccharide of glycophorin A is di-branched and more than 50% of this sugar chain is monosialylated, type A HA+-PTX probably bound to the unsialylated branch of the N-linked oligosaccharide of glycophorin A and agglutinated erythrocytes. One subcomponent of HA, designated HA1, did not agglutinate native erythrocytes, although it did bind to erythrocytes, paragloboside and asialoglycoproteins in a manner quite similar to that of HA+-PTX. These results indicate that type A HA+-PTX binds to oligosaccharides through HA1.

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