Which of the following produces a bacterial toxin that attaches to presynaptic nerves and blocks the release of acetylcholine?
1- Helicobactor pylori
2- Clostridium difficile
3- clostridium botulinum
4- staphylococcus aureus
5 - pseudomonas aeruginosa
choice 3
MODE OF ACTION OF BOTULINUM NEUROTOXINS
Botulism poisoning is evidenced by paralysis in which the toxin binds to receptors on the peripheral nerve endings, blocking synaptic transmission of signal to the muscle fibers. Synaptic transmission to nerves supplying muscle fibers requires the release of acetyl choline neurotransmitter from synaptic vesicles in the nerve endings. Botulinum toxin acts in a 3-step process:
a) binding to a receptor on the nerve ending
b) internalization of part of the molecule into the nerve cell
c) inhibition of release of neurotransmitter (acetylcholine).
Different toxin types recognize different receptors on the nerve cell and it is the C-terminus of the heavy chain (H) that is associated with binding to the nerve cell.
Recent studies have shown that type B neurotoxin (BoNT/B) binds to the amino terminal of a 58 kDa integral membrane protein (synaptotagmin II) of synaptic vesicles (Nishiki et al., 1996). Further studies with recombinant synaptotagmin II have indicated high affinity binding by BoNT/B and suggests that this may be the native receptor for BoNT/B. Synaptotagmin is also highly conserved among animal species. The significance is that synaptotagmin is suggested to be involved with Ca+2-dependent exocytosis of synaptic vesicles at the nerve ending.
