期刊
EUROPEAN JOURNAL OF BIOCHEMISTRY
卷 267, 期 15, 页码 4668-4675出版社
BLACKWELL SCIENCE LTD
DOI: 10.1046/j.1432-1327.2000.01518.x
关键词
A chain; B chain; beta-bungarotoxin; evolutionary divergence; genetic organization
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 A(2) genes indicated that genetic divergence of the A chain and phospholipase A(2)s was in accordance with their family. Moreover, evolutionary divergence of the intron and exon regions of the A chain, as observed for phospholipase A(2) 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.
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