title: The role of the proteinase inhibitor ovorubin in apple snail eggs resembles plant embryo defense against predation.
abstract: BACKGROUND
  Fieldwork has thoroughly established that most eggs are intensely predated. Among the few exceptions are the aerial egg clutches from the aquatic snail Pomacea canaliculata which have virtually no predators. Its defenses are advertised by the pigmented ovorubin perivitellin providing a conspicuous reddish coloration. The nature of the defense however, was not clear, except for a screening for defenses that identified a neurotoxic perivitellin with lethal effect on rodents. Ovorubin is a proteinase inhibitor (PI) whose role to protect against pathogens was taken for granted, according to the prevailing assumption. Through biochemical, biophysical and feeding experiments we studied the proteinase inhibitor function of ovorubin in egg defenses.
  
  
  RESULTS
  Mass spectrometry sequencing indicated ovorubin belongs to the Kunitz-type serine proteinase inhibitor family. It specifically binds trypsin as determined by small angle X-ray scattering (SAXS) and cross-linking studies but, in contrast to the classical assumption, it does not prevent bacterial growth. Ovorubin was found extremely resistant to in vitro gastrointestinal proteolysis. Moreover feeding studies showed that ovorubin ingestion diminishes growth rate in rats indicating that this highly stable PI is capable of surviving passage through the gastrointestinal tract in a biologically active form.
  
  
  CONCLUSIONS
  To our knowledge, this is the first direct evidence of the interaction of an egg PI with a digestive protease of potential predators, limiting predator's ability to digest egg nutrients. This role has not been reported in the animal kingdom but it is similar to plant defenses against herbivory. Further, this would be the only defense model with no trade-offs between conspicuousness and noxiousness by encoding into the same molecule both the aposematic warning signal and an antinutritive/antidigestive defense. These defenses, combined with a neurotoxin and probably unpalatable factors would explain the near absence of predators, opening new perspectives in the study of the evolution and ecology of egg defensive strategies.
authors.affiliation: Instituto de Investigaciones Bioquímicas de La Plata (INIBIOLP), CONICET-Universidad Nacional de La Plata, La Plata, Argentina.
authors.forename: Marcos Sebastián
authors.initials: MS
authors.lastname: Dreon
authors.forename: Santiago
authors.initials: S
authors.lastname: Ituarte
authors.forename: Horacio
authors.initials: H
authors.lastname: Heras
mesh_terms: D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology; D004527:Egg Proteins / Q000737:chemistry / Q000494:pharmacology*; D005260:Female; D005767:Gastrointestinal Diseases / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008297:Male; D011235:Predatory Behavior; D011480:Protease Inhibitors / Q000494:pharmacology*; D017434:Protein Structure, Tertiary; D051381:Rats; D017422:Sequence Analysis, DNA; D012908:Snails; D053719:Tandem Mass Spectrometry / Q000379:methods; D013696:Temperature; D014357:Trypsin / Q000737:chemistry
chemical_list: D000890:Anti-Infective Agents; D004527:Egg Proteins; D011480:Protease Inhibitors; C002008:ovorubin; D014357:Trypsin