Binding activity and immunogenic characterization of recombinant C-terminal quarter and half of the heavy chain of botulinum neurotoxin serotype A.

In the present study, we explored and compared the binding activity and immunogenic characterization of the most effective part corresponding to C-terminal quarter of heavy chain of botulinum neurotoxin serotype A (AHc-C) with C-terminal half of heavy chain of botulinum neurotoxin serotype A (AHc). Firstly, the fully soluble AHc-C protein successfully expressed in Escherichia coli by co-expression with thioredoxin (Trx) was shown to bind with ganglioside as the AHc, indicating that the recombinant AHc-C protein retains a functionally active conformation. Furthermore, a solid-phase assay showed that the anti-AHc-C sera effectively inhibited the binding of AHc or AHc-C to the ganglioside GT1b, the first step in BoNT/A intoxication of neurons, as good as the anti-AHc sera. Finally, although the recombinant AHc-C protein still induced a high serum antibody titers and afforded protection level as the mice challenged with active botulinum neurotoxin serotype A, the immunization with AHc protein induced stronger protective potency than the AHc-C protein. The data presented in the report shows that there are the same ganglioside binding activity and different immunogenic characterization between the C-terminal quarter and half of heavy chain of botulinum neurotoxin serotype A. Therefore, the recombinant AHc-C protein can not only be developed into a minimal subunit candidate vaccine for prophylaxis against botulinum neurotoxin serotype A but also be used as a promising tool in the search for binding inhibitors and chimeric vaccines.