Geographic differentiation and cryptic diversity in the monocled cobra, Naja kaouthia (Elapidae) from Thailand

South‐East Asia has an exceptionally high diversity of snakes, with more than 250 snake species currently recorded from Thailand. This diversity likely reflects the diverse range of geographical and climatic conditions under which they live, but the evolutionary history and population genetics of many snake species in South‐East Asia have been little investigated in comparison with morphological studies. Here, we investigated genetic variation in the monocled cobra, Naja kaouthia, Lesson, 1831, across its distribution range in Thailand using mitochondrial DNA (cytochrome b, control region) for ~100 individuals and the nuclear DNA gene (C‐mos) for a small subset. Using population genetic and phylogenetic methods, we show high levels of genetic variation between regional populations of this non‐spitting cobra, including the north‐eastern, north‐central and southern regions, in addition to a population on Pha‐ngan Island, 150 km offshore from the southern peninsula. Moreover, inclusion of the north‐eastern population renders N. kaouthia paraphyletic in relation to other regional Naja species. The north‐eastern population is therefore probably specifically distinct. Given that these cobras are otherwise undifferentiated based on colour and general appearance to the “typical” cobra type of this region, they would represent a cryptic species. As has been shown in other animal groups from Thailand, it is likely that the geographical characteristics and/or tectonic alteration of these regions have facilitated high levels of population divergence of N. kaouthia in this region. Our study highlights the need for dense sampling of snake populations to reveal their systematics, plan conservation and facilitate anti‐snake venom development

Novel long-chain neurotoxins from Bungarus candidus distinguish the two binding sites in muscle-type nicotinic acetylcholine receptors

αδ-Bungarotoxins, a novel group of long-chain α-neurotoxins, manifest different affinity to two agonist/competitive antagonist binding sites of muscle-type nicotinic acetylcholine receptors, being more active at the interface of α-δ-subunits. Three isoforms (αδ-BgTx-1-3) were identified in Malayan Krait ( Bungarus candidus ) from Thailand by genomic DNA analysis; two of them (αδ-BgTx-1 and 2) were isolated from its venom. The toxins comprise 73 amino acid residues and 5 disulfide bridges, being homologous to α-bungarotoxin (α-BgTx), a classical blocker of muscle-type and neuronal α7, α8, and α9α10 nicotinic acetylcholine receptors. The toxicity of αδ-BgTx-1 (LD50 0.17-0.28 μg/g mouse, i.p. injection) is essentially as high as that of α-BgTx. In the chick biventer cervicis nerve-muscle preparation, αδ-BgTx-1 completely abolished acetylcholine response, but in contrast to the block by α-BgTx, acetylcholine response was fully reversible by washing. αδ-BgTxs, similar to α-BgTx, bind with high affinity to α7 and muscle-type nicotinic acetylcholine receptors. However, the major difference of αδ-BgTxs from α-BgTx and other naturally-occurring α-neurotoxins is that αδ-BgTxs discriminate the two binding sites in the Torpedo californica and mouse muscle nicotinic acetylcholine receptors showing up to two orders of magnitude higher affinity for the α-δ site as compared to α-ε or α-γ binding site interfaces. Molecular modeling and analysis of the literature provided possible explanations for these differences in binding mode; one of the probable reasons being the lower content of positively charged residues in αδ-BgTxs. Thus, αδ-BgTxs are new tools for studies on nicotinic acetylcholine receptors

Novel long-chain neurotoxins from Bungarus candidus distinguish the two binding sites in muscle-type nicotinic acetylcholine receptors

αδ-Bungarotoxins, a novel group of long-chain α-neurotoxins, manifest different affinity to two agonist/competitive antagonist binding sites of muscle-type nicotinic acetylcholine receptors, being more active at the interface of α-δ-subunits. Three isoforms (αδ-BgTx-1-3) were identified in Malayan Krait ( Bungarus candidus ) from Thailand by genomic DNA analysis; two of them (αδ-BgTx-1 and 2) were isolated from its venom. The toxins comprise 73 amino acid residues and 5 disulfide bridges, being homologous to α-bungarotoxin (α-BgTx), a classical blocker of muscle-type and neuronal α7, α8, and α9α10 nicotinic acetylcholine receptors. The toxicity of αδ-BgTx-1 (LD50 0.17-0.28 μg/g mouse, i.p. injection) is essentially as high as that of α-BgTx. In the chick biventer cervicis nerve-muscle preparation, αδ-BgTx-1 completely abolished acetylcholine response, but in contrast to the block by α-BgTx, acetylcholine response was fully reversible by washing. αδ-BgTxs, similar to α-BgTx, bind with high affinity to α7 and muscle-type nicotinic acetylcholine receptors. However, the major difference of αδ-BgTxs from α-BgTx and other naturally-occurring α-neurotoxins is that αδ-BgTxs discriminate the two binding sites in the Torpedo californica and mouse muscle nicotinic acetylcholine receptors showing up to two orders of magnitude higher affinity for the α-δ site as compared to α-ε or α-γ binding site interfaces. Molecular modeling and analysis of the literature provided possible explanations for these differences in binding mode; one of the probable reasons being the lower content of positively charged residues in αδ-BgTxs. Thus, αδ-BgTxs are new tools for studies on nicotinic acetylcholine receptors

Novel long-chain neurotoxins from Bungarus candidus distinguish the two binding sites in muscle-type nicotinic acetylcholine receptors

αδ-Bungarotoxins, a novel group of long-chain α-neurotoxins, manifest different affinity to two agonist/competitive antagonist binding sites of muscle-type nicotinic acetylcholine receptors, being more active at the interface of α-δ-subunits. Three isoforms (αδ-BgTx-1-3) were identified in Malayan Krait ( Bungarus candidus ) from Thailand by genomic DNA analysis; two of them (αδ-BgTx-1 and 2) were isolated from its venom. The toxins comprise 73 amino acid residues and 5 disulfide bridges, being homologous to α-bungarotoxin (α-BgTx), a classical blocker of muscle-type and neuronal α7, α8, and α9α10 nicotinic acetylcholine receptors. The toxicity of αδ-BgTx-1 (LD50 0.17-0.28 μg/g mouse, i.p. injection) is essentially as high as that of α-BgTx. In the chick biventer cervicis nerve-muscle preparation, αδ-BgTx-1 completely abolished acetylcholine response, but in contrast to the block by α-BgTx, acetylcholine response was fully reversible by washing. αδ-BgTxs, similar to α-BgTx, bind with high affinity to α7 and muscle-type nicotinic acetylcholine receptors. However, the major difference of αδ-BgTxs from α-BgTx and other naturally-occurring α-neurotoxins is that αδ-BgTxs discriminate the two binding sites in the Torpedo californica and mouse muscle nicotinic acetylcholine receptors showing up to two orders of magnitude higher affinity for the α-δ site as compared to α-ε or α-γ binding site interfaces. Molecular modeling and analysis of the literature provided possible explanations for these differences in binding mode; one of the probable reasons being the lower content of positively charged residues in αδ-BgTxs. Thus, αδ-BgTxs are new tools for studies on nicotinic acetylcholine receptors

Novel long-chain neurotoxins from Bungarus candidus distinguish the two binding sites in muscle-type nicotinic acetylcholine receptors

αδ-Bungarotoxins, a novel group of long-chain α-neurotoxins, manifest different affinity to two agonist/competitive antagonist binding sites of muscle-type nicotinic acetylcholine receptors, being more active at the interface of α-δ-subunits. Three isoforms (αδ-BgTx-1-3) were identified in Malayan Krait ( Bungarus candidus ) from Thailand by genomic DNA analysis; two of them (αδ-BgTx-1 and 2) were isolated from its venom. The toxins comprise 73 amino acid residues and 5 disulfide bridges, being homologous to α-bungarotoxin (α-BgTx), a classical blocker of muscle-type and neuronal α7, α8, and α9α10 nicotinic acetylcholine receptors. The toxicity of αδ-BgTx-1 (LD50 0.17-0.28 μg/g mouse, i.p. injection) is essentially as high as that of α-BgTx. In the chick biventer cervicis nerve-muscle preparation, αδ-BgTx-1 completely abolished acetylcholine response, but in contrast to the block by α-BgTx, acetylcholine response was fully reversible by washing. αδ-BgTxs, similar to α-BgTx, bind with high affinity to α7 and muscle-type nicotinic acetylcholine receptors. However, the major difference of αδ-BgTxs from α-BgTx and other naturally-occurring α-neurotoxins is that αδ-BgTxs discriminate the two binding sites in the Torpedo californica and mouse muscle nicotinic acetylcholine receptors showing up to two orders of magnitude higher affinity for the α-δ site as compared to α-ε or α-γ binding site interfaces. Molecular modeling and analysis of the literature provided possible explanations for these differences in binding mode; one of the probable reasons being the lower content of positively charged residues in αδ-BgTxs. Thus, αδ-BgTxs are new tools for studies on nicotinic acetylcholine receptors