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Crystal structure of Clostridium botulinum neurotoxin type B in complex with the inhibitor reveals that during the course of enzyme inhibition, the active site rearranges and zinc ion is gradually removed from the active site causing loss of catalytic activity.

Results show that the endopeptidase botulinum neurotoxin type A occurs as a monomer in crystal structures and as a dimer in solution but dissociating into monomeric form under low concentration levels. Data further demonstrate that the catalytic activity of the monmer is about four-fold higher than dimer foms.

The role of the C-terminus of synaptosomal-associated protein of Mr = 25 kDa (SNAP-25) in exocytosis was analyzed in the large-core vesicles of intact and detergent-permeabilized bovine adrenochromaffin cells. The administration of type A botulinum neurotoxin (BoNTA) in bovine adrenochromaffin cells cleaved SNAP-25 and attenuated exocytotic responses to K+-depolarization. The effects of BoNTA on exocytosis indicated the functional role of specific regions in SNAP-25 during the various stages of the exocytotic process.

The action of BoNT-A and -E in neuronal cultures is examined, to understand how each serotype enters neurons. The uptake of BoNT-A and -E is enhanced with synaptic activity and the translocation of the toxin catalytic moiety into the cytosol occurs at different rates.