The Clostridium neurotoxin family is composed of tetanus neurotoxins and seven serotypes of botulinum neurotoxin. The structure of the botulinum neurotoxin reveals a four domain protein. The N-terminal catalytic domain (Pfam:PF01742), the central translocation domains and two receptor binding domains [1]. This domains is the C-terminal receptor binding domain, which adopts a modified beta-trefoil fold with a six stranded beta-barrel and a beta-hairpin triplet capping the domain [1]. The first step in the intoxication process is a binding event between this domains and the pre-synaptic nerve ending [1].

1: Crystal structure of botulinum neurotoxin type A and implications for toxicity. Lacy DB, Tepp W, Cohen AC, DasGupta BR, Stevens RC; Nat Struct Biol 1998;5:898-902. PMID:9783750