Specific antibodies against the Zn(2+)-binding domain of clostridial neurotoxins restore exocytosis in chromaffin cells treated with tetanus or botulinum A neurotoxin.

Although tetanus and botulinum A neurotoxins are ineffective in cultured chromaffin cells, they will inhibit carbachol-induced release of noradrenaline provided they gain access to the cytosol either through artificial pores generated in the plasma membrane or by binding to incorporated exogenous gangliosides. The block of exocytosis persists for weeks followed by a slow recovery of cell function. When specific anti-botulinum A toxin antibodies are introduced into cells through pores after manifestation of the block by botulinum A neurotoxin, restoration of exocytotic function is accelerated and fully reestablished within 4 days. The same time course of restoration is seen with anti-tetanus toxin antibodies in cells poisoned by tetanus toxin. Since the light chains of the toxins are enzymatically active, we have introduced polyclonal and monoclonal anti-light chain antibodies into the cytosol. Of all light chain antibodies tested, only those directed against the peptide homologous to the zinc-binding sequence, which is present in both neurotoxins, restored exocytosis regardless of which toxin caused the block. These results indicate that the zinc-binding domain is directly involved in the interaction of the light chains with their substrates and that the toxins have to be present continuously to maintain the block.