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]
^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. PMID7096305.
^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. doi:10.1016/j.toxicon.2007.10.006. PMID18037462.
^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. PMID9027977.
