FUSION COMPLEX-FORMATION PROTECTS SYNAPTOBREVIN AGAINST PROTEOLYSIS BY TETANUS TOXIN LIGHT-CHAIN

The clostridial neurotoxin, tetanus toxin, is a Zn2+-dependent proteas e which inhibits neurotransmitter exocytosis by selective cleavage of the synaptic vesicle protein, synaptobrevin. Synaptobrevin is thought to serve as a receptor for two neuronal plasma membrane proteins, synt axin and SNAP-25, which in the presence of non-hydrolyzable ATP analog s form a 20 S fusion complex with the soluble fusion proteins NSF and alpha-SNAP. Here we show that synaptobrevin, when in this 20 S complex , or its 7 S precursor, is protected against proteolysis by the enzyma tically active tetanus toxin light chain. Our data define distinct poo ls of synaptobrevin, which provide markers of different steps of vesic le/plasma membrane interaction.