β-Bungarotoxin is a form ofbungarotoxin that is fairly common inKrait (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 confersphospholipase A2 (PLP A2) activity, and the B chain, likedendrotoxins, have aKunitz 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 thepresynaptic terminal, where it blocks release ofacetylcholine. It seems to do so by blocking the phosphorylation ofMARCKS.[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.
^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.
