Botulinum neurotoxin type B complex with zinc ion and inhibitor (bis(5-amidino-2-benzimidazolyl)methane)
Clostridium botulinum (bacteria)
A very popular recent cosmetic treatment for wrinkles is called botox. Botox can be injected into the skin and then weakens or paralyzes the nerves which control the muscles. Other than for such cosmetic uses, botox has also been successfully employed to treat involuntary rhythmic muscle contraction and twitching. While some bacterial toxins like diphtheria or cholera toxin cause cell death, other like C.botulinum neurotoxin (botox) or tetanus toxin, block release of neurotransmitters and thus disrupt the signaling system of nerves. Botulinum and tetanus toxins are highly potent poisons, more than one thousands times as deadly as for instance diphtheria toxin. While C. tetani produces only one type of neurotoxin, the bacterium C.botulinum produces seven different types of such toxins. Despite having a completely different mode of action from diphtheria toxin, they have a similar basic overall structure.
The toxin is built from two domains, a catalytic A domain and a binding B domain. The B domain, consisting of two subdomains, both of them mostly beta-sheet structure, contains a binding site for sugars that reside on the cell surface. The A domain is divided into two functional domains. Connecting to the B subunit is a long mainly alpha-helical translocation domain. This domain helps with transporting the catalytic domain through the cell membrane. The structure here shows the toxin with a zinc ion and a sulfate ion. A related structure of the toxin with no legand shows in PDB:1EPW. A related structure of the toxin complex with sialyllactose shows in PDB:1F31.
Protein Data Bank (PDB)
Eswaramoorthy, S. Kumaran, D. Swaminathan, S.; "A Novel Mechanism for Clostridium botulinum Neurotoxin Inhibition"; Biochemistry; (2002) 41:9795-9802 PubMed:12146945.
author: Arno Paehler