CHARACTERIZATION OF CLOSTRIDIUM-BOTULINUM TYPE-B NEUROTOXIN ASSOCIATED WITH INFANT BOTULISM IN JAPAN

The neurotoxin of strain 111 (111/NT) associated with type B infant bo tulism showed antigenic and biological properties different from that (Okra/NT) produced by a food-borne botulism-related strain, Okra, The specific toxicity of 111/NT was found to be about 10 times lower than that of Okra/NT, The monoclonal antibodies recognizing the light chain cross-reacted with both neurotoxins, whereas most of the antibodies r ecognizing the carboxyl-terminal half of the heavy chain of Okra/NT di d not react to 111/NT, Binding experiments with rat brain synaptosomes revealed that I-125-labeled 111/NT bound to a single binding site wit h a dissociation constant (K-d) of 2.5 nM; the value was rather lower than that (0.42 nM) of I-125-Okra/NT for the high-affinity binding sit e. In the lipid vesicles reconstituted with ganglioside GT1b, I-125-Ok ra/NT interacted with the amino-terminal domain of synaptotagmin 1 (St g1N) or synaptotagmin 2 (Stg2N), fused with the maltose-binding protei n, in the same manner as the respective full-length synaptotagmins, an d the K-d values accorded with those of the low- and high-affinity bin ding sites in synaptosomes. However, I-125-111/NT only exhibited a low capacity for binding to the lipid vesicles containing Stg2N, but not Stg1N, in the presence of ganglioside GT1b, Moreover, synaptobrevin-2, an intracellular target protein, was digested to the same extent by t he light chains of both neurotoxins in a concentration-dependent manne r. These findings indicate that the 111/NT molecule possesses the rece ptor-recognition site structurally different from Okra/NT, probably ca using a decreased specific toxicity.