DIRECT VISUALIZATION OF BOTULINUM NEUROTOXIN-INDUCED CHANNELS IN PHOSPHOLIPID-VESICLES

THE seven botulinum neurotoxin (NT) serotypes produced by strains of C lostridium botulinum inhibit neurotransmitter release from synaptic ve sicles. Neurotoxin is synthesized as a roughly 150K single-chain prote in. Proteolysis produces two fragments, the 50K L-chain and 100K H-cha in, that remain linked by a disulphide bond. Intoxication involves mem brane attachment by the C-terminal half of the H-chain, endocytotic/ly sosomal internalization, vesicle channel formation mediated by the 50K N-terminal half of the H-chain at low pH, and finally blockade of syn aptic vesicle fusion after the L-chain reaches the cytosol1-4 . We rep ort here the visualization of the neurotoxin-membrane complex by elect ron cryomicroscopy and image processing. Three-dimensional reconstruct ions show the neurotoxin bound to the exterior of ganglioside/PC lipid vesicles and show channels entirely perforating the vesicle wall. Eac h channel appears to arise from the interaction of four neurotoxin mol ecules.