High resolution crystal structures of the receptor-binding domain of Clostridium botulinum neurotoxin serotypes A and FA.

The binding specificity of botulinum neurotoxins (BoNTs) is primarily a consequence of their ability to bind to multiple receptors at the same time. BoNTs consist of three distinct domains, a metalloprotease light chain (LC), a translocation domain (H(N)) and a receptor-binding domain (H(C)). Here we report the crystal structure of H(C)/FA, complementing an existing structure through the modelling of a previously unresolved loop which is important for receptor-binding. Our H(C)/FA structure also contains a previously unidentified disulphide bond, which we have also observed in one of two crystal forms of H(C)/A1. This may have implications for receptor-binding and future recombinant toxin production.