期刊
MOLECULAR BIOLOGY AND EVOLUTION
卷 35, 期 4, 页码 887-898出版社
OXFORD UNIV PRESS
DOI: 10.1093/molbev/msx334
关键词
gene duplication; evolutionary biophysics; evolutionary innovation; exaptation; venom
资金
- National Science Foundation [DEB 1145987]
- BioProject Agkistrodon contortrix [SRR2032114]
- BioProject Agkistrodon piscivoros [SRR2032118]
- BioProject Crotalus adamanteus [SRR441163]
- BioProject Crotalus atrox [SRR5270430]
- BioProject Crotalus cerastes [SRR5270834]
- BioProject Crotalus horridus A [SRR575168]
- BioProject Crotalus horridus B [SRR1554232]
- BioProject Crotalus lepidus [SRR5270851]
- BioProject Crotalus mitchellii [SRR5270850]
- BioProject Crotalus tigris [SRR5270853]
- BioProject Crotalus scutulatus [SRR5270449]
- BioProject Sistrurus catenatus [SRR2029826]
- BioProject Sistrurus miliarius [SRR2031930]
- [PRJNA88989]
Evolutionary innovations and complex phenotypes seemingly require an improbable amount of genetic change to evolve. Rattlesnakes display two dramatically different venom phenotypes. Type I venoms are hemorrhagic with low systemic toxicity and high expression of tissue-destroying snake venom metalloproteinases. Type II venoms are highly neurotoxic and lack snake venom metalloproteinase expression and associated hemorrhagic activity. This dichotomy hinges on Mojave toxin (MTx), a phospholipase A(2) (PLA2) based beta-neurotoxin expressed in Type II venoms. MTx is comprised of a nontoxic acidic subunit that undergoes extensive proteolytic processing and allosterically regulates activity of a neurotoxic basic subunit. Evolution of the acidic subunit presents an evolutionary challenge because the need for high expression of a nontoxic venom component and the proteolytic machinery required for processing suggests genetic changes of seemingly little immediate benefit to fitness. We showed that MTx evolved through a cascading series of exaptations unlocked by a single nucleotide change. The evolution of one new cleavage site in the acidic subunit unmasked buried cleavage sites already present in ancestral PLA2s, enabling proteolytic processing. Snake venom serine proteases, already present in the venom to disrupt prey hemostasis, possess the requisite specificities for MTx acidic subunit proteolysis. The dimerization interface between MTx subunits evolved by exploiting a latent, but masked, hydrophobic interaction between ancestral PLA2s. The evolution of MTx through exaptation of existing functional and structural features suggests complex phenotypes that depend on evolutionary innovations can arise from minimal genetic change enabled by prior evolution.
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