top of page

Venom expression in rattlesnakes – mechanisms of regulation of activity and control of venom synthesis

Mackessy, Stephen P.

School of Biological Sciences

University of Northern Colorado

Greeley, Colorado USA

Castoe, Todd A.

Perry, Blair W.

Schield, Drew R.

Department of Biology

University of Texas

Arlington, Texas USA

The evolution of a chemical means of dispatching prey has provided numerous advantages to venomous snakes, but it has also presented them with a conundrum: how are venoms stored for long periods of time, instantly available for dispatching prey or warding off predators, but not undergoing degradation or intoxicating the snake? Rattlesnake venoms are rich in enzymatic components, and metalloproteinases (SVMPs) are particularly abundant in type I venoms. In general, expressed venoms are stable and show relatively little degradation even when stored in liquid form under less-than-ideal conditions. However, when purified, numerous components are much more labile, and metalloproteinases in particular are subject to autolytic degradation. We sought to investigate how venoms can be expressed into the ductules and basal lumen of the gland and stored for long periods of time, often years in captive snakes, without a loss in potency or endangering the snake. We used a variety of techniques, including protein chemistry, electron microscopy, histochemical and immunochemical staining of glands, and time course gene expression analyses to address mechanisms of regulation of venom secretion and storage. Several redundant mechanisms exist that protect the snake from venom toxins and maintain venom patency, including the presence of high concentration/low abundance tripeptide SVMP inhibitors and maintenance of the venom at an acidic (pH = 5.4) pH. Localized upregulation of vacuolar H+-ATPases (but not H-K ATPases) was demonstrated via Western blots and immunological staining, strongly supporting our earlier hypothesis that mitochondria-rich cells are responsible for venom bolus acidification. Together, these mechanisms allow for safe storage of a labile, toxic protein solution (venom) for long periods of time, inactive while in the gland but immediately activated upon deployment (prey tissues are ~2 log steps higher pH), again demonstrating that venomous snakes can serve as informative model systems for the investigation of novel regulatory mechanisms.