A Neurotoxin, Toxin α, from Egyptian Cobra (Naja haje haje) Venom: I. PURIFICATION, PROPERTIES, AND COMPLETE AMINO ACID SEQUENCE

Abstract

A neurotoxin, designated toxin α, has been isolated from the venom of the Egyptian cobra (Naja haje haje) by gradient chromatography on Amberlite CG-50, and has been further purified by gel filtration on Sephadex G-50. Homogeneity was verified by free boundary electrophoresis, acrylamide gel electrophoresis, sedimentation velocity, amino acid analysis, and end group analysis. Toxin α has a sedimentation constant, s020, w, of 1.18 S, a diffusion constant, D20, w of 14.07 × 10−7 cm2 sec−1, electrophoretic mobilities of 6.02 × 10−5, 2.94 × 10−5, and 2.84 × 10−5 cm2 sec−1 volt−1 at pH 5.0, 6.8, and 8.3, respectively, and a formula weight of 6834.6. Ultracentrifugation studies indicate that the reduced, S-carboxymethylated toxin is capable of dimer formation. Chemical studies show that toxin α is a small, basic protein consisting of a single polypeptide chain of 61 amino acid residues, cross-linked by four disulfide bridges. Alanine, methionine, and phenylalanine are totally absent. The complete amino acid sequence of the neurotoxin was determined by analyzing tryptic and chymotryptic peptides of the S-carboxymethyl derivative of the neurotoxin. Alignment with the partially determined structure of the probably homologous neurotoxin α from Naja nigricollis indicates eight amino acid differences between the two neurotoxins.