Amino Acid Sequence of β2-Bungarotoxin from Bungarus multicinctus Venom. The Amino Acid Substitutions in the B Chains

Abstract

beta 2-Bungarotoxin (beta 2-toxin) was isolated from the venom of Bungarus multicinctus by means of CM-Sephadex C-25 column chromatography, Sephadex G-75 gel filtration and CM-Sephadex C-25 column rechromatography. beta 2-Toxin consisted of two dissimilar polypeptides, a (120 amino acid residues) and B (60 amino acid residues) chains, crosslinked by an interchain disulfide bond. The neurotoxicity (LD50) and phospholipase activity of beta 2-toxin were 0.029 micrograms/g of mouse and 48.9 units/mg of toxin, respectively, and both the activities were slightly weaker than those (0.019 micrograms/g and 60.9 units/mg) of beta 1-bungarotoxin (beta 1-toxin). beta 2-Toxin was reduced and carboxymethylated and then its RCM-A and -B chains were separated. Each RCM-chain was maleylated and then digested with TPCK-trypsin. The tryptic peptides were sequences by manual Edman degradation or the dansyl-Edman method, and the total alignment of the tryptic peptides from each RCM-chain was deduced based on the amino acid sequences of the A and B chains of beta 1-toxin. The amino acid sequence of the B chain of beta 2-toxin differed from that of the B chain of beta 1-toxin by 22 amino acid substitutions, while those of their A chains were identical. We concluded that the variation in the amino acid sequence of the B chains did not significantly affect the neurotoxicity of the beta-toxins. The amino acid sequences of the B chains of the two beta-toxins were homologous to those of proteinase inhibitors from snake venoms and mammalian pancreas, but no inhibitory activity of the two beta-toxins on proteinases was observed.

Phospholipase A2 activity of β‐bungarotoxin is essential for induction of cytotoxicity on cerebellar granule neurons

“…This toxin consists of two polypeptide chains linked by a disulphide bond (Kondo et al, 1978a(Kondo et al, , 1982. Polypeptide chain A is a phospholipase A 2 (PLA 2 ) subunit having 120 amino acid residues, which shows a remarkable structural similarity to other vertebrate basic PLA 2 enzymes (Kini and Evans, 1987).…”

The essentiality of B chain in stabilizing the structure of the A chain in β1-bungarotoxin fromBungarus multicinctus venom

“…Among them, ill-and fl2-Bgt have an identical amino acid sequence in their A chains and remarkable differences in their B chain. The neurotoxicity (LDs0) and PLA2 activity of fl2-Bgt were 0.029/~g/g of mouse and 48.9 U/mg of toxin, respectively, and both the activities were weaker than (0.019/~g/g and 60.9U/rag) of fil-Bgt (Kondo et al, 1982a). These results again implied that the B chain might affect the function role of the A chain played in /3~-Bgt, probably through protein-protein interactions between the A chain and the B chain.…”

Protease Inhibitors from Marine Venomous Animals and Their Counterparts in Terrestrial Venomous Animals

“…CaC specifically blocks most of the high-threshold Ca 2+ channels in the nanomolar range, specially the L-type component of the Ca 2+ current [111,112]. β-Bungarotoxin was previously isolated from Bungarus multicinctus venom and comprises two dissimilar polypeptide chains, the A chain (~14 kDa) and B chain (~7 kDa), which are linked by an interchain disulfide bridge [113]. The B chain of β-bungarotoxin is homologous to venom basic protease inhibitors but, similar to most of dendrotoxins, displays no protease inhibitory activity and also blocks voltage-gated K + channels [114].…”