Analysis of absorption of Clostridium botulinum toxins from the small infestine

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Clostridium botulinum strains produce seven immunologically distinct neurotoxins, from types A to G. The molecular mass (Mr) of all types of neurotoxins is approximately 150 kDa. The neurotoxins are associated with non-toxic component in cultures or in foods, and become large complexes designated progenitor toxins. Type, B, C, and D strains produce two forms of progenitor toxin, M (300 kDa, 12S toxin) and L (500 kDa, 16S toxin), and type A produces M, L, and LL toxins. The M toxin consists of a neurotoxin and a non-toxic component showing no haemagglutinin (HA) activity, which is described as non-toxic non-HA. The L toxin is formed by conjugation of M toxin with HA. The LL toxin is a dimer of L toxin. Recently we found that HA consists of four subcomponents designated HA1 (~33 kDa), HA2 (~17 kDa), HA3a (~23 kDa), and HA3b (~53 kDa), and that type C-L toxin is effectively absorbed from the small intestine than M toxin and neurotoxin. This time, binding of A-L and -LL toxins (designated HA^+-PT) and recombinant four HA subcomponents to erythrocytes or the epithelial cells of guinea pig-small intestine were analyzed. It became clear that HA^+-PTX bound epithelial cells and erythrocytes mainly via HA1, and its receptor was Galβ-1-4GlcNac. In case of type C, it seemed that L toxin bound to the cells via both HA1 and HA3b, and the receptor of HA1 and HA3b was sialyl lactose and sialic acid, respectively.The importance of C-HA1 for the binding of L toxin to the cells was further confirmed by analysing two mutant L toxins with low HA activity and by preparing monoclonal antibodies against HA1.