Isolation and primary structure of the major toxin from sea snake, Acalyptophis peronii, venom

Diet Breadth Mediates the Prey Specificity of Venom Potency in Snakes

Venoms are best known for their ability to incapacitate prey. In predatory groups, venom potency is predicted to reflect ecological and evolutionary drivers relating to diet. While venoms have been found to have preyspecific potencies, the role of diet breadth on venom potencies has yet to be tested at large macroecological scales. Here, using a comparative analysis of 100 snake species, we show that the evolution of prey-specific venom potencies is contingent on the breadth of a species' diet. We find that while snake venom is more potent when tested on species closely related to natural prey items, we only find this prey-specific pattern in species with taxonomically narrow diets. While we find that the taxonomic diversity of a snakes' diet mediates the prey specificity of its venom, the species richness of its diet was not found to affect these prey-specific potency patterns. This indicates that the physiological diversity of a species' diet is an important driver of the evolution of generalist venom potencies. These findings suggest that the venoms of species with taxonomically diverse diets may be better suited to incapacitating novel prey species and hence play an important role for species within changing environments.

Structure, function and evolution of three-finger toxins: mini proteins with multiple targets

Snake venoms are complex mixtures of pharmacologically active peptides and proteins. These protein toxins belong to a small number of superfamilies of proteins. Three-finger toxins belong to a superfamily of non-enzymatic proteins found in all families of snakes. They have a common structure of three beta-stranded loops extending from a central core containing all four conserved disulphide bonds. Despite the common scaffold, they bind to different receptors/acceptors and exhibit a wide variety of biological effects. Thus, the structure-function relationships of this group of toxins are complicated and challenging. Studies have shown that the functional sites in these 'sibling' toxins are located on various segments of the molecular surface. Targeting to a wide variety of receptors and ion channels and hence distinct functions in this group of mini proteins is achieved through a combination of accelerated rate of exchange of segments as well as point mutations in exons. In this review, we describe the structural and functional diversity, structure-function relationships and evolution of this group of snake venom toxins.

Isolation and chemical characterization of a toxin isolated from the venom of the sea snake, Hydrophis torquatus aagardi

Sea snakes (family: Hydrophiidae) are serpents found in the coastal areas of the Indian and Pacific Oceans. There are two subfamilies in Hydrophiidae: Hydrophiinae and Laticaudinae. A toxin, aagardi toxin, was isolated from the venom of the Hydrophiinae snake, Hydrophis torquatus aagardi and its chemical properties such as molecular weight, isoelectric point, importance of disulfide bonds, lack of enzymatic activity and amino acid sequence were determined. The amino acid sequence indicated a close relationship to the primary structure of other Hydrophiinae toxins and a significant difference from Laticaudinae toxins, confirming that primary toxin structure is closely related to sea snake phylogenecity.

Comparison of sea snake (Hydrophiidae) neurotoxin to cobra (Naja) neurotoxin

Both sea snakes and cobras have venoms containing postsynaptic neurotoxins. Comparison of the primary structures indicates many similarities, especially the positions of the four disulfide bonds. However, detailed examination reveals differences in several amino acid residues. Amino acid sequences of sea snake neurotoxins were determined, and then compared to cobra neurotoxins by computer modeling. This allowed for easy comparison of the similarities and differences between the two types of postsynaptic neurotoxins. Comparison of computer models for the toxins of sea snakes and cobra will reveal the three dimensional difference of the toxins much clearer than the amino acid sequence alone.

Expression pattern of three-finger toxin and phospholipase A2 genes in the venom glands of two sea snakes, Lapemis curtus and Acalyptophis peronii: comparison of evolution of these toxins in land snakes, sea kraits and sea snakes

Background

Snake venom composition varies widely both among closely related species and within the same species, based on ecological variables. In terrestrial snakes, such variation has been proposed to be due to snakes' diet. Land snakes target various prey species including insects (arthropods), lizards (reptiles), frogs and toads (amphibians), birds (aves), and rodents (mammals), whereas sea snakes target a single vertebrate class (fishes) and often specialize on specific types of fish. It is therefore interesting to examine the evolution of toxins in sea snake venoms compared to that of land snakes.

Results

Here we describe the expression of toxin genes in the venom glands of two sea snakes, Lapemis curtus (Spine-bellied Sea Snake) and Acalyptophis peronii (Horned Sea Snake), two members of a large adaptive radiation which occupy very different ecological niches. We constructed cDNA libraries from their venom glands and sequenced 214 and 192 clones, respectively. Our data show that despite their explosive evolutionary radiation, there is very little variability in the three-finger toxin (3FTx) as well as the phospholipase A₂ (PLA₂) enzymes, the two main constituents of Lapemis curtus and Acalyptophis peronii venom. To understand the evolutionary trends among land snakes, sea snakes and sea kraits, pairwise genetic distances (intraspecific and interspecific) of 3FTx and PLA₂ sequences were calculated. Results show that these proteins appear to be highly conserved in sea snakes in contrast to land snakes or sea kraits, despite their extremely divergent and adaptive ecological radiation.

Conclusion

Based on these results, we suggest that streamlining in habitat and diet in sea snakes has possibly kept their toxin genes conserved, suggesting the idea that prey composition and diet breadth may contribute to the diversity and evolution of venom components.

Molecular cloning, expression and characterization of three short chain alpha-neurotoxins from the venom of sea snake--Hydrophiinae Hydrophis cyanocinctus Daudin

Three different genes named sn311, sn316 and sn285 were discovered by large-scale randomly sequencing the high quality cDNA library of the venom glands from Hydrophiinae Hydrophis cyanocinctus Daudin. Sequence analysis showed that these three genes encoded three different short chain alpha-neurotoxins of 81 amino acids, which contained a signal peptide of 21 amino acids and followed by a mature peptide of 60 amino acids. Amino acid comparison reveals that mature peptides of sn311 and sn316 are highly homologous, with the only variance at position 46, which is Lys46 and Ser46, respectively. Whereas the mature peptide of sn285 lacks the most conserved amino acids in short chain alpha-neurotoxins, Asp31 and Arg33. The coding sequences of three neurotoxins were cloned into a thioredoxin (TRX) fusion expression vector (pTRX) and expressed as soluble recombinant fusion proteins in E. coli. After purification, approximately 10 mg/l recombinant proteins with the purity up to 95% were obtained. These three recombinant proteins are designated as rSN311, rSN316 and rSN285, they have a molecular weight of 6.963, 6.920 and 6.756 kDa, respectively, which are similar to those predicted from amino acid sequences. LD50 values of rSN311, rSN316 and rSN285 are 0.0827, 0.095, and 0.0647 mg/kg to mice, respectively. Studies on effects of these recombinant proteins on neuromuscular transmission were carried out, and results indicate that they all can produce prompt blockade of neuromuscular transmission, but display distinct biological activity characteristic individually. The results from UV-circular dichroism (CD) spectra indicate that they share similar secondary structure compared to other identified alpha-neurotoxins, and no significant structural differences in these recombinant proteins are observed.

Postsynaptic short-chain neurotoxins from Pseudonaja textilis. cDNA cloning, expression and protein characterization

Two lethal proteins, which specifically bind to the nAChR from Torpedo californica, were isolated from the venom of Pseudonaja textilis, the common brown snake from Australia. The isolated proteins have masses of 6236 and 6345 Da and are structurally related to short-chain neurotoxins from other elapids. Six cDNAs encoding isoforms of related neurotoxins were cloned using the RT-PCR of the venom gland mRNAs. The sequences of the corresponding proteins consist of 57-58 amino acid residues and display several unique features when compared with all known short-chain neurotoxins. Accordingly, they grouped separately in phylogenetic analysis. The six cDNAs were expressed in Escherichia coli and the recombinant proteins were characterized. They have similar masses and display similar toxicities and binding constants to the nAChR as the native toxins isolated from the venom. Thus, a new group of short-chain postsynaptic neurotoxins from the venom of an Australian elapid has been characterized.

Purification and characterization of Contractin A from the pedicellarial venom of sea urchin, Toxopneustes pileolus

A component that causes contraction of the isolated guinea pig tracheal smooth muscle was isolated in homogeneous form from the venom of the pedicellaria of the sea urchin, Toxopneustes pileolus. It is named Contractin A. Contractin A has 18,000 Da with a total residue of 138 amino acids. The molecular weight is about 17,700. The N-terminal amino acid is serine. The partial amino acid sequence was determined up to 37 residues. Direct comparison of sea urchin Contractin A does not show any similarity in amino acid sequence to toxins isolated from other marine toxin producers such as sea snakes, sea anemones, or marine worms. Contractin A caused contraction of the tracheal smooth muscle in a dose-dependent manner. Furthermore, Contractin A relaxed the contraction induced by histamine. The contraction and relaxation activity of Contractin A on the tracheal smooth muscle is reduced by a cyclooxygenase inhibitor such as indomethacin. The contraction induced by Contractin A is also inhibited by a phospholipase C inhibitor but not by a phospholipase A2 inhibitor. These results suggest that in the isolated guinea pig tracheal smooth muscle, the response to Contractin A may be effected through activated phospholipase C.

Amino-acid sequence of the minor neurotoxin from Acalyptophis peronii venom

Sea snakes, Acalyptophis peronii, were captured in the Gulf of Thailand and their venom was isolated. A. peronii venom contains two neurotoxins called major and minor toxin. The complete amino-acid sequence of the minor toxin was identified and compared to that of the major toxin. The only difference between the major and the minor toxins is in the 43rd residue. The major toxin at this position contains glutamine, while the minor toxin contains glutamic acid. The LD50 of the minor toxin is 0.170 microgram/g in mice when injected intravenously. The toxicity is slightly lower than that of the major toxins, which has an LD50 of 0.125 microgram/g.