Botulinum neurotoxins comprise seven distinct serotypes (A-G) produced by
Clostridium botulinum. The crystal structure of the binding domain of the
botulinum neurotoxin type B (BBHc) has been determined to 2A resolution. The
overall structure of BBHc is well ordered and similar to that of the binding
domain of the holotoxin. However, significant structural changes occur at what
would be the interface of translocation and binding domains of the holotoxin.
The loop 911-924 shows a maximum displacement of 14.8A at the farthest point.
The N-terminal helix reorients and moves by 19.5A from its original position.
BBHc is compared with the binding domain of the holotoxin of botulinum type A
and B, and the tetanus C-fragment to characterize the heavy chain-carbohydrate
interactions. The probable reasons for different binding affinity of botulinum
and tetanus toxins are discussed.