Evolution of phospholipase A-2 venom proteins across Rattlesnakes (genera Crotalus and Sistrurus)


Broussard, Emilie M.

ebroussard@bio.fsu.edu


Hogan, Michael P.

Rokyta, Darin R.

Department of Biological Sciences

Florida State University

Tallahassee, Florida USA


Phospholipase A-2 (PLA2) proteins belong to a gene family of enzymes that are found across the animal kingdom and have been recruited as a toxin in many animal venoms. Rattlesnake (genera Crotalus and Sistrurus) venom consists of a cocktail of proteins and toxins that include a repertoire of PLA2s. These PLA2s contribute to the split in venom type observed in rattlesnakes between Type I and Type II venom, which have different pharmacological effects. To better understand the evolutionary history of this ecologically important gene family in rattlesnakes, we searched the transcriptomes of 198 individuals from 35 subspecies of Crotalus and Sistrurus for PLA2 sequences. Recovered sequences were used to construct a phylogeny, which identified clades for the acidic and basic subunits of the PLA2 proteins, as well as a clade of the neurotoxic Mojave Toxin sequences which characterize the Type 2 venom. Domains and functional sites of the recovered sequences were identified and Fixed Effects Likelihood (FEL) and Mixed Effects Model of Evolution (MEME) tests were performed to identify sites under purifying and positive selection.