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 (pfam01742), the central translocation domains and two receptor binding domains. 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. The role of this domain in receptor binding appears to be indirect.