Abstract
Envenomation of humans by snakes is a complex and continuously evolving medical emergency, and treatment is made that much more difficult by the diverse biochemical composition of many venoms. Venomous snakes and their venoms also provide models for the study of molecular evolutionary processes leading to adaptation and genotype-phenotype relationships. To compare venom complexity and protein sequences, venom gland transcriptomes are assembled, which usually requires the sacrifice of snakes for tissue. However, toxin transcripts are also present in venoms, offering the possibility of obtaining cDNA sequences directly from venom. This study provides evidence that unknown full-length venom protein transcripts can be obtained from the venoms of multiple species from all major venomous snake families. These unknown venom protein cDNAs are obtained by the use of primers designed from conserved signal peptide sequences within each venom protein superfamily. This technique was used to assemble a partial venom gland transcriptome for the Middle American Rattlesnake (Crotalus simus tzabcan) by amplifying sequences for phospholipases A2, serine proteases, C-lectins, and metalloproteinases from within venom. Phospholipase A2 sequences were also recovered from the venoms of several rattlesnakes and an elapid snake (Pseudechis porphyriacus), and three-finger toxin sequences were recovered from multiple rear-fanged snake species, demonstrating that the three major clades of advanced snakes (Elapidae, Viperidae, Colubridae) have stable mRNA present in their venoms. These cDNA sequences from venom were then used to explore potential activities derived from protein sequence similarities and evolutionary histories within these large multigene superfamilies. Venom-derived sequences can also be used to aid in characterizing venoms that lack proteomic profiles and identify sequence characteristics indicating specific envenomation profiles. This approach, requiring only venom, provides access to cDNA sequences in the absence of living specimens, even from commercial venom sources, to evaluate important regional differences in venom composition and to study snake venom protein evolution.
Highlights
The evolution of venoms among the advanced colubroid snakes has had tremendous adaptive significance and has allowed this clade to diversify rapidly and occupy a diversity of niches globally [1]
This study provides evidence that unknown full-length venom protein transcripts can be obtained from the venoms of multiple species from all major venomous snake families
Phospholipase A2 sequences were recovered from the venoms of several rattlesnakes and an elapid snake (Pseudechis porphyriacus), and three-finger toxin sequences were recovered from multiple rear-fanged snake species, demonstrating that the three major clades of advanced snakes (Elapidae, Viperidae, Colubridae) have stable mRNA present in their venoms
Summary
The evolution of venoms among the advanced colubroid snakes has had tremendous adaptive significance and has allowed this clade to diversify rapidly and occupy a diversity of niches globally [1]. Snake venoms are complex glandular secretions that may contain 2–100+ protein/ peptide components with a myriad of biological activities, ranging from potent neurotoxins to rapid-acting myotoxins to hydrolytic enzymes [2]. These toxins are synthesized and stored in a cephalic venom gland which allows immediate deployment as a chemical weapon, necessitating intricate storage and protective mechanisms [3]. Venoms likely allowed a transition from mechanical capture and processing of prey to one dependent on chemical means [4], and during the approximately 100 million year history of snakes [5], a diversity of biochemical compositional “strategies” have evolved [6, 7]. Determining detailed venom composition among differing lineages of snakes can provide important connections linking phenotypic variation to specific selective pressures, and linking venom composition to snakebite envenomation effects
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