| κ-Bungarotoxin | |
| Organism: | Bungarus multicinctus |
| Taxid: | 8616 |
| Symbol: | N/A |
| Pdb: | 1KBA |
| Uniprot: | P01398 |
κ-Bungarotoxin (often written κ-Bgt; historically also called toxin F[1]) is a protein neurotoxin of the bungarotoxin family that is found in the venom of the many-banded krait, a snake found in Taiwan. κ-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.[2]
κ-Bungarotoxin was first reported in 1983 as a component of the venom of Bungarus multicinctus that differed in biological effect from the previously known α-bungarotoxin: κ-bungarotoxin, but not α-bungarotoxin, was capable of impeding nicotinic signaling in the chick ciliary ganglion.[3] Bungarotoxin toxin was designated "kappa" as an allusion to the Latin word kiliaris ("from the eye"), and to the root of "ciliary".[3] Separately identified toxins designated "toxin F" and "bungarotoxin 3.1" were identified by protein sequencing as identical to κ-bungarotoxin.
κ-Bungarotoxin binds to the nicotinic acetylcholine receptors of the autonomic ganglia, predominantly to the nicotinic receptor subunit alpha 3 (CHRNA3) and to a lesser extent alpha 4. Two distinct binding surfaces, both on the N-terminal extracellular face of the receptor subunit, have been identified.[4]
κ-Bungarotoxin is a receptor antagonist, meaning it blocks the normal response of the receptor to acetylcholine, which inhibits neurotransmission and therefore causes neuromuscular paralysis. Like the α-bungarotoxins, κ-bungarotoxin causes a post-synaptic blockade of signaling; this is in contrast to the β-bungarotoxins which induce a pre-synaptic block. The distinction between the effects of α-bungarotoxin and κ-bungarotoxin was first identified functionally, as differences in effects on specific neural structures.[5] The basis of this functional difference has been molecularly characterized as differences in receptor subtype specificity; the pentameric receptors are assembled from different distributions of subunits in neurons and in muscles.
The κ-bungarotoxin polypeptide is 66 amino acids long and folds into an antiparallel beta sheet structure stabilized by five conserved disulfide bonds, a structural feature shared by many peptide toxins. Unlike other members of the bungarotoxin family, κ-bungarotoxin is a dimer.[6]