Clostridium botulinum produces seven neurotoxin (NTX) serotypes, classified from as A to G. In culture, NTX forms protein complexes by association with non-toxic components, such as nontoxic-nonhemagglutinin (NTNH) and hemagglutinins (HA1, HA2, HA3). C. botulinum serotype A produces three types of toxin complexes, M-toxin (NTX and NTNH), L-toxin (M-toxin and HAs) and LL-toxin (dimer of L-toxin). In this study, I found three HA complexes in the culture of a nontoxigenic mutant serotype A lacking ntx and ntnh expression. The HA complexes displayed similar banding patterns on SDS-PAGE, but the staining intensities of the HA1 and HA2 bands were different. In addition, their native-PAGE banding profiles exhibited different behaviors. The large-molecular-size HA complex showed the highest activity, similar to that of an L-toxin. Based on the combined results of the PAGE and gel-filtration profiles, the differences in molecular size among the three HA complexes were thought to be caused by different numbers of HA1 and HA2 molecules. This paper reports for the first time the purification and characterization of a native HA complex of serotype A, and suggests that the HA can form complex structures without NTX and NTNH. This may help in understanding the toxin complex assembly pathway.
タンパク質複合体構造（protein complex structure）