BIOCHEMISTRY AND PHARMACOLOGY OF COLUBRID SNAKE VENOMS

Abstract

The polyphyletic family Colubridae contains approximately two-thirds of the described species of advanced snakes, and nearly half of these (∼700 species) produce a venom in a specialized cephalic gland, the Duvernoy's gland. Biochemical and pharmacological information is lacking for venoms of most species, and modest detailed information on venom composition is available for only a few species which represent a potential health threat to humans. However, colubrid venoms represent a vast source of novel compounds, and some toxins, such as the 20–26 kD CRISP-related venom proteins (helveprins), have only recently been identified in both colubrid and elapid/viperid venoms. Difficulties associated with extraction have been addressed, and it is now possible to obtain venom sufficient for many analyses from even small species. There appears to be a greater number of venom components shared among the colubrids and the front-fanged snakes than has been previously noted, and it is probable that as analytical methods improve, more similarities will emerge. It is clear that colubrid venoms are homologous with front-fanged snake venoms, but overall composition as well as biological role(s) of colubrid venoms may be quite different. Metallo- and serine proteases have been identified in several colubrid venoms, and phospholipase A₂ is a more frequent component than has been previously recognized. Venom phosphodiesterase, acetylcholinesterase and prothrombin activator activities occur in some venoms, and postsynaptic neurotoxins and myotoxins have been partially characterized for venoms from several species. Some venoms show high toxicity toward inbred mice, and others are toxic to birds and/or frogs only. Because many colubrids feed on non-mammalian prey, lethal toxicity toward mice is likely only relevant as a measure of potential risk posed to humans. Development of a non-mammalian vertebrate animal model would greatly facilitate systematic comparisons of the pharmacology of colubrid venoms and their components, and such a model would be more appropriate for evaluation of colubrid venom toxicity. Proteomics has the potential to increase our understanding of these venoms rapidly, but classical approaches to toxinology can also contribute tremendously to this understudied field. As more colubrid venoms are analyzed, new compounds unique to colubrid venoms will be identified, and this work in turn will lead to a better understanding of the evolution and biological significance of snake venoms and venom components.

Keywords: :

• Acetylcholinesterase
• Helveprins
• Metalloprotease
• Neurotoxin
• Phosphodiesterase
• Phospholipase A₂
• Serine protease
• Toxin
• Venom evolution