Molecular cloning of the major lethal toxins from two kraits (Bungarus flaviceps and Bungarus candidus).
The major lethal toxins present in the venoms of the red-headed krait, Bungarus flaviceps, and the Malayan krait, Bungarus candidus, have both been purified. Each consists of two polypeptide chains, A and B, joined by a disulfide bond. In the present study, primary structures of these toxins were determined by Edman degradation and by nucleotide sequencing of the cDNA clones. Amino acid sequencing of the N-terminus and enzymatically digested peptides revealed that the A and B chains were highly homologous to those of beta-bungarotoxins (beta-Bgts) from Bungarus multicinctus, respectively. We isolated cDNA clones encoding the A and B chains from both B. flaviceps and B. candidus venom gland cDNA libraries using probes designed based on the cDNA sequence of beta-Bgt from B. multicinctus. Two isoforms of the A chain and one isoform of the B chain were obtained from B. flaviceps, and one isoform of the A chain and two isoforms of the B chain were obtained from B. candidus. Both of the two A chains from B. flaviceps are made up of 119 amino acids and comprise 15 cysteine residues, while the A chains of beta-Bgt from other Bungarus species including B. candidus comprise 13 cysteine residues. The B chains from both species are composed of 59 amino acid residues and comprise seven cysteines. In conclusion, the lethal toxin from B. flaviceps is considered to be a novel isoform of beta-Bgt, which has a different pattern of cysteine residues from known beta-Bgts.
Yanoshita
Ryohei
R
Institute of Medicinal Chemistry, Hoshi University, Tokyo 142-8501, Japan.
Ogawa
Yuko
Y
Murayama
Nobuhiro
N
Omori-Satoh
Tamotsu
T
Saguchi
Ken-Ichi
K
Higuchi
Shigesada
S
Khow
Orawan
O
Chanhome
Lawan
L
Samejima
Yuji
Y
Sitprija
Visith
V
D000595:Amino Acid Sequence; D002038:Bungarotoxins / Q000737:chemistry / Q000302:isolation & purification / Q000633:toxicity*; D003001:Cloning, Molecular / Q000379:methods*; D018076:DNA, Complementary / Q000302:isolation & purification*; D010802:Phylogeny; D016133:Polymerase Chain Reaction
D002038:Bungarotoxins; D018076:DNA, Complementary