Bungarotoxin

Bungarotoxins are a group of closely related neurotoxic proteins derived from the venom of kraits including Bungarus multicinctus. α-Bungarotoxin inhibits the binding of acetylcholine (ACh) to nicotinic acetylcholine receptors; β- and γ-bungarotoxins act presynaptically causing excessive acetylcholine release and subsequent depletion. Both α and β forms have been characterized, the α being similar to the long or Type II neurotoxins from other elapid venoms.

There are four types:

History

Banded Krait venom began to be studied by Chuan-Chiung Chang and Chen-Yuan Lee of the National Taiwan University in the 1950s; however, it was not until 1963 that its components were separated and isolated.

References

Kappa-bungarotoxin

Kappa-bungarotoxin (often written κ-Bgt; historically also called toxin F) is a protein neurotoxin of the bungarotoxin family that is found in the venom of the many-banded krait, a snake found in Taiwan. Kappa-bungarotoxin is a high affinity antagonist of nicotinic acetylcholine receptors (nAChRs), particularly of CHRNA3; it causes a post-synaptic blockade of neurotransmission. Although there is significant variability in the clinical effects of snake bites, neuromuscular paralysis and respiratory failure are associated with krait bites.

Discovery

Kappa-bungarotoxin was first reported in 1983 as a component of the venom of Bungarus multicinctus that differed in biological effect from the previously known alpha-bungarotoxin: Kappa, but not alpha, was capable of impeding nicotinic signaling in the chick ciliary ganglion. The newly discovered toxin was designated "kappa" as an allusion to the Latin word kiliaris ("from the eye"), also the root of "ciliary". Separately identified toxins designated "toxin F" and "bungarotoxin 3.1" were identified by protein sequencing as identical to kappa-bungarotoxin.

Alpha-bungarotoxin

α-Bungarotoxin (α-BTX) is one of the bungarotoxins, components of the venom of the elapid snake Taiwanese banded krait (Bungarus multicinctus). It is a type of α-neurotoxin, a neurotoxic protein that is known to bind competitively and in a relatively irreversible manner to the nicotinic acetylcholine receptor found at the neuromuscular junction, causing paralysis, respiratory failure and death in the victim. It has also been shown to play an antagonistic role in the binding of the α7 nicotinic acetylcholine receptor in the brain, and as such has numerous applications in neuroscience research.

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.