Antigenic structure of Clostridium botulinum type B neurotoxin and its interaction with gangliosides, cerebroside, and free fatty acids

A fragment distinct from the heavy and light chains was obtained by treatment of Clostridium botulinum type B neurotoxin with chymotrypsin. Enzyme-linked immunosorbent assay and immunoblotting analysis with monoclonal antibodies showed that the fragment consisted of the light chain and part of the heavy chain (H-1 fragment) linked together by a disulfide bond. Monoclonal antibodies reacting to the heavy chain but not to the fragment were thought to recognize the epitopes on the remaining portion (H-2 fragment) of the heavy chain, being easily digested by chymotrypsin. Thus, the antigenic structure of type B neurotoxin resembles those of type A and E neurotoxins. The chymotrypsin-induced fragment bound to cerebroside and free fatty acids but not to gangliosides. The manner of binding of type B neurotoxin to gangliosides and free fatty acids was different from those of type A and E neurotoxins. Such differences in the reactivities to lipids may be related to the finding that each neurotoxin binds to a type-specific site on the neural membrane.