ABSTRACT
A gene encoding the full-size botulinum neurotoxin serotype C was reconstructed in vector pQE-30 and expressed at high levels in Escherichia coli. Three amino acid mutations (H229-->G, E230-->T, and H233-->N) were generated in the zinc-binding motif, resulting in complete detoxification of the modified recombinant holotoxin. The PCR-amplified wild-type light chain of botulinum neurotoxin serotype C was also expressed in E. coli and used as a control in all experiments. Modified recombinant holotoxin and light chain contained a histidine affinity tag at the amino terminus, which was used for detection and purification. Recombinant proteins were purified on nickel affinity resin and analyzed by Western blotting with the anti-histidine tag and anti-neurotoxin C antibodies. The results indicated that the 150-kDa molecule of modified recombinant holotoxin and the 50-kDa recombinant light chain were synthesized without degradation; however, E. coli did not provide for efficient nicking of modified recombinant toxin. Modified recombinant holotoxin was not toxic to mice, had no effect on nerve-evoked muscle twitch in vitro, and was not able to cleave syntaxin in crude synaptosome preparations. The recombinant light chain was also nontoxic in vivo, had no effect on evoked muscle twitch, but was able to cleave syntaxin. Modified recombinant neurotoxin and light chain were administered to animals either orally or subcutaneously. Both oral administration and subcutaneous administration of modified recombinant neurotoxin evoked high levels of serum antibodies and protective immunity. Oral administration of recombinant light chain evoked no systemic response, whereas subcutaneous administration evoked antibody production and immunity.
