Endocytosis of Clostridium botulinum type B neurotoxin into rat brain synaptosomes

Clostridium botulinum type B neurotoxin cleaves VAMP (vesicle-associated me mbrane protein)/synaptobrevin into two fragments, which results in inhibiti on of neurotransmitter release. The induced fragment did not react to the a ntibody raised against the synthetic peptide of the amino-terminal 20 resid ues of VAMP-2, suggesting that the toxin treatment has caused antigenical a lteration in the amino-terminal region of VAMP-2. In rat brain synaptosomes , type B neurotoxin was reduced presumably with sulfhydryls in the membrane and detected in the synaptic vesicle fraction which involved the degradati on of VAMP-2 and the inhibition of neurotransmitter release. The light chai n in a free form was present in the cytosol fraction. These findings sugges t a possibility that type B neurotoxin endocytoses into synaptic vesicles b y the recycling pathway and the light chain is penetrable through synaptic vesicle membrane. However, the amount of type B neurotoxin entrapped into s ynaptic vesicles appears to be extremely small, which may be attributed to a lower sensitivity of the toxin to brain synaptosomes than to peripheral n erve endings.