Structure
α-Bungarotoxin is a 74 amino acid, 8 kDa α-neurotoxin with five disulfide bridges that binds as a competitive antagonist to nicotinic acetylcholine receptors (nAChRs). As with other snake venom α-neurotoxins, it has a three-finger fold tertiary structure, which is a four disulfide globular core from which emerge three loops (fingers) and a C-terminal tail. The tips of fingers I and II form a mobile region that is essential for proper binding.
Hydrogen bonds allow for an anitparallel β-sheet, which keeps the second and third loops roughly parallel. The three-finger structure is preserved by four of the disulfide bridges: the fifth can be reduced without loss to toxicity. The fifth bridge is located on the tip of the second loop.
The multiple disulfide bonds and small amount of secondary structure seen in α-BTX is the cause of the extreme stability of this kind of neurotoxin. Since there are many entropically viable forms of the molecule, it does not denature easily, and has been shown to be resistant to boiling. and strong acids
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