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β-Bungarotoxin
β-Bungarotoxin
	Schematic diagram of the three-dimensional structure of β2-bungarotoxin (PDB: 1bun)
Identifiers
Organism	Bungarus multicinctus
Symbol	N/A
CAS number	12778-32-4 ; β1:65862-89-7; β2:82446-04-6

β-Bungarotoxin is a form of bungarotoxin that is fairly common in Krait (Bungarus multicinctus) venoms. It is the prototypic class of snake β-neurotoxins. There are at least five isoforms, coded β₁ to β₅, assembled from different combinations of A and Bchains.^[1]

The toxin is a heterodimer of two chains. The A chain confers phospholipase A2 (PLP A2) activity, and the B chain, like dendrotoxins, have a Kunitz domain. There are many isoforms of these chains: examples of A chains include A1 (P00617), A3 (P00619), and A4 (P17934), and examples of B chains include B2 (P00989) and B3 (Q75S50). The B chain plays a functional role in inducing apoptosis.^[2]

The target of this neurotoxin is at the presynaptic terminal, where it blocks release of acetylcholine. It seems to do so by blocking the phosphorylation of MARCKS.^[3] It is thought that the dendrotoxin-like B chain acts first by inhibition of ion channels, causing cessation of twitches followed by a prolonged facilitatory phase. The A chain (bearing phospholipase activity) then induces a blocking phase by destruction of phospholipids.^[4]

Binding sites

Neurobiological research from the late 1980s has found that beta-bungarotoxin selectively binds to (125)I-DTX-I receptor.

References

^ Kondo, K; Toda, H; Narita, K; Lee, CY (May 1982). "Amino acid sequences of three beta-bungarotoxins (beta 3-, beta 4-, and beta 5- bungarotoxins) from Bungarus multicinctus venom. Amino acid substitutions in the A chains". Journal of Biochemistry. 91 (5): 1531–48. doi:10.1093/oxfordjournals.jbchem.a133844. PMID 7096305.
^ Cheng YC, Wang JJ, Chang LS (February 2008). "B chain is a functional subunit of beta-bungarotoxin for inducing apoptotic death of human neuroblastoma SK-N-SH cells". Toxicon. 51 (2): 304–15. Bibcode:2008Txcn...51..304C. doi:10.1016/j.toxicon.2007.10.006. PMID 18037462.
^ Ueno, E; Rosenberg, P (1996). "Mechanism of action of beta-bungarotoxin, a presynaptically acting phospholipase A2 neurotoxin: its effect on protein phosphorylation in rat brain synaptosomes". Toxicon. 34 (11–12): 1219–27. doi:10.1016/S0041-0101(96)00113-4. PMID 9027977.
^ Rowan, EG (January 2001). "What does beta-bungarotoxin do at the neuromuscular junction?". Toxicon. 39 (1): 107–18. Bibcode:2001Txcn...39..107R. doi:10.1016/S0041-0101(00)00159-8. PMID 10936627.