Genetic organization of A chain and B chain of β‐bungarotoxin from Taiwan banded krait (Bungarus multicinctus)

Abstract

b-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 b-bungarotoxin molecules should be derived from the pairing of A and B chains after their mRNAs are translated.Keywords: A chain; B chain; b-bungarotoxin; evolutionary divergence; genetic organization.b-Bungarotoxin (b-Bgt), the main presynaptic neurotoxin purified from the venom of Bungarus multicinctus (Taiwan banded krait) [1±3], is one of the most investigated presynaptic neurotoxins from snake venoms. The toxin consists of two dissimilar polypeptide chains, the A chain with 120 amino-acid residues and the B chain with 61 residues, cross-linked by an interchain disulfide bond, and possesses a weak phospholipase A 2 (PLA 2 ) activity [4,5]. The amino-acid sequences of A chains are structurally homologous with those of PLA 2 s from snake venoms and mammalian pancreas [2,3]. B chains share sequence similarity with the trypsin inhibitor, toxin I, toxin K and dendrotoxin [6±8]. Kondo et al. [3] and Kini & Iwanaga [9] suggested that the A chain is an active subunit that is responsible for the PLA 2 enzymatic activity and neurotoxic effect of b-Bgt, while the B chain may serve as a recognition subunit of the toxin to a specific target cell membrane. Nevertheless, Benishin [10] suggested that the B chain might be responsible for the blockage of certain voltage-gated potassium channels in a manner that did not involve the A chain. Recent studies on the recombinant B chain supported this suggestion [11].The molecular structures of PLA 2 s with presynaptic neurotoxicity are quite varied. Some of these structures are single polypeptide chains, such as notexin and ammodytoxin, whereas others are binary (b-Bgt, crotoxin), ternary (taipoxin) or pentanary (textilotoxin) complexes [12]. Besides b-Bgt and the two textilotoxin D subunits, ...

Phylogenetic resolution power of microsatellites and various single‐nucleotide polymorphism types assessed in 10 divergent chicken populations

“…Thus, the various marker types reflect common evolutionary effects as well as marker‐type‐specific events. These findings are in agreement with previous reports of Wu & Chang () and Lyamouri et al . (), but differ from Chang et al .…”

“…However, the contribution of these different SNP types to phylogenetic analysis has not been thoroughly investigated. Several studies have noted discordance between phylogenetic analysis of snakes and flies based on exons and introns (Wu & Chang ; Lyamouri et al . ).…”

Common evolution of waprin and kunitz-like toxin families in Australian venomous snakes

“…This is reflected in the larger size of the mature kunitz-type inhibitors Research Article 4047 compared to the waprin proteins by approximately nine amino acids. The overall domain arrangement, (including intron/exon boundaries sites) of the kunitztype inhibitor genes from Australian elapids closely reflects that of the only other known kunitz genes from two other snakes: a putative chymotrypsin inhibitor from the Taiwan cobra, Naja atra, and the B chain isoforms of the potassium channel blocker bbungarotoxin from the Taiwan banded krait, Bungarus multicinctus [5,31,32]. Indeed, the Textilinin-2 gene sequence demonstrates 87 % identity to the N. atra sequence, whilst it is less similar to the bbungarotoxin B1 chain gene, primarily due to the presence of a greater than 1kb insertion within the second intron of this sequence.…”

Kinetic analysis of effects of temperature and time on the regulation of venom expression in Bungarus multicinctus

“…In addition, they became an important farmed species in china because of high medicinal and economic value, and have therefore attracted considerable research attention. Their venom compositions have been studied intensively over the past decades 14 – 17 . However, there have been no reports of the time- and temperature-dependent dynamic changes of the venom system in B. multicinctus , although temperature is an important environmental factor in the regulation of snake venom composition.…”