Genetic organization of A chain and B chain of beta-bungarotoxin from Taiwan banded krait (Bungarus multicinctus). A chain genes and B chain genes do not share a common origin.
beta-Bungarotoxin, the main presynaptic neurotoxin purified from the venom of Bungarus multicinctus, consists of two dissimilar polypeptide chains, the A chain and the B chain, cross-linked by an interchain disulfide bond. In this study, A and B chain genes isolated from the liver of B. multicinctus encoded the A and B chain precursors, respectively. Analyses of the coding regions of the A and B chain genes revealed that both consist of three exons and two introns. The sequences of all exon/intron junctions agree with the GT/AG rule. However, sequence alignment and phylogenetic analysis did not support that the evolution of A and B chain genes are closely related. Comparative analysis of A chain genes with Viperinae and Crotalinae phospholipase A2 genes indicated that genetic divergence of the A chain and phospholipase A2s was in accordance with their family. Moreover, evolutionary divergence of the intron and exon regions of the A chain, as observed for phospholipase A2 genes, was not consistent. Noticeably, the transcription of A and B chain genes may be regulated under different transcription factors as revealed by analyses of their promoter sequences. In terms of the finding that A and B chains are encoded separately by different genes, this strongly supports the view that the intact beta-bungarotoxin molecules should be derived from the pairing of A and B chains after their mRNAs are translated.
Wu
P F
PF
Institute of Biomedical Sciences, National Sun Yat-Sen University, Taiwan.
Chang
L S
LS
D000595:Amino Acid Sequence; D000818:Animals; D002038:Bungarotoxins / Q000737:chemistry / Q000235:genetics*; D017838:Bungarus; D004220:Disulfides; D019143:Evolution, Molecular; D005091:Exons; D015723:Gene Library; D007438:Introns; D008099:Liver / Q000737:chemistry; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D014176:Protein Biosynthesis; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic
D002038:Bungarotoxins; D004220:Disulfides