The Clostridium neurotoxin family is composed of tetanus neurotoxin 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 N-terminal receptor binding domain,which is comprised of two seven-stranded beta-sheets sandwiched together to form a jelly role motif [1]. The role of this domain in receptor binding appears to be indirect.

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