Abstract
BackgroundSnake venoms are complex mixtures of pharmacologically active proteins and peptides which belong to a small number of superfamilies. Global cataloguing of the venom transcriptome facilitates the identification of new families of toxins as well as helps in understanding the evolution of venom proteomes.ResultsWe have constructed a cDNA library of the venom gland of a threatened rattlesnake (a pitviper), Sistrurus catenatus edwardsii (Desert Massasauga), and sequenced 576 ESTs. Our results demonstrate a high abundance of serine proteinase and metalloproteinase transcripts, indicating that the disruption of hemostasis is a principle mechanism of action of the venom. In addition to the transcripts encoding common venom proteins, we detected two varieties of low abundance unique transcripts in the library; these encode for three-finger toxins and a novel toxin possibly generated from the fusion of two genes. We also observed polyadenylated ribosomal RNAs in the venom gland library, an interesting preliminary obsevation of this unusual phenomenon in a reptilian system.ConclusionThe three-finger toxins are characteristic of most elapid venoms but are rare in viperid venoms. We detected several ESTs encoding this group of toxins in this study. We also observed the presence of a transcript encoding a fused protein of two well-characterized toxins (Kunitz/BPTI and Waprins), and this is the first report of this kind of fusion in a snake toxin transcriptome. We propose that these new venom proteins may have ancillary functions for envenomation. The presence of a fused toxin indicates that in addition to gene duplication and accelerated evolution, exon shuffling or transcriptional splicing may also contribute to generating the diversity of toxins and toxin isoforms observed among snake venoms. The detection of low abundance toxins, as observed in this and other studies, indicates a greater compositional similarity of venoms (though potency will differ) among advanced snakes than has been previously recognized.
Highlights
Snake venoms are complex mixtures of pharmacologically active proteins and peptides which belong to a small number of superfamilies
26 families of toxins have been catalogued in snake venom proteomes, and several families appear to be specific to a particular family of venomous snakes (Additional file 1)
Sarafotoxins are found only in venoms of Atractaspididae; serine proteinases related to blood coagulation factors Xa, cobra venom factor, waprins and AVIT family peptides appear to be limited to the Elapidae; and vascular endothelial growth factor (VEGF), disintegrins, waglerins, dipeptidyl peptidase IV and crotamine occur primarily in venoms of the Viperidae (Additional file 1)
Summary
Snake venoms are complex mixtures of pharmacologically active proteins and peptides which belong to a small number of superfamilies. The advanced snakes (superfamily Colubroidea) consist of a monophyletic group of four families: Atractaspididae, "Colubridae", Elapidae and Viperidae [1]. These snakes have evolved biochemical weapon (toxins), rather than mechanical means of handling prey. 26 families of toxins have been catalogued in snake venom proteomes, and several families appear to be specific to a particular family of venomous snakes (Additional file 1). Sarafotoxins are found only in venoms of Atractaspididae; serine proteinases related to blood coagulation factors Xa, cobra venom factor, waprins and AVIT (prokineticin) family peptides appear to be limited to the Elapidae; and vascular endothelial growth factor (VEGF), disintegrins, waglerins, dipeptidyl peptidase IV and crotamine occur primarily in venoms of the Viperidae (Additional file 1). Despite overall similarity in clinical symptoms exhibited after envenomation by members of a particular family of snakes, there exists considerable species-specific variation in absolute effects within each group, contributing to the difficulty in assessing and treating envenomated victims
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