kappa-Bungarotoxin: complete amino acid sequence of a neuronal nicotinic receptor probe.

The complete amino acid sequence of kappa-bungarotoxin, a neurotoxin isolated from the venom of the banded krait Bungarus multicinctus, has been determined by automated Edman analyses of the intact protein and peptides derived from digests with trypsin and chymotrypsin. kappa-Bungarotoxin consists of a single polypeptide chain of 66 amino acids with a molecular weight of 7313. It contains 10 cysteinyl residues, presumably arranged in 5 disulfide bonds, and is completely devoid of methionine and tryptophan. The amino acid sequence of kappa-bungarotoxin shows greatest homology to the curaremimetic postsynaptic long neurotoxins of which alpha-bungarotoxin is also a member. However, there are some striking differences between kappa-bungarotoxin and other members of this group which may explain its unusual ability to block neuronal acetylcholine receptors.