Antinutritive perivitellins in Pomacea Perry, 1810: The case of P. scalaris (d’Orbigny, 1835) (Architaenioglossa, Ampullariidae)

ITUARTE,S.; DREON, M.S.; HERAS, H.

Quebec

Congreso; Physiomar 10; 2010

Ampullariids exhibit two oviposition strategies: basal clades lay egg masses below waterline while the most derived groups lay colored egg clutches outside the water. The shift to aerial oviposition was a key event of Ampullariidae evolution which required physiological innovations as eggs are exposed for weeks to direct sunlight, high temperature, desiccation and predators. Apple snail egg proteins, perivitellins, were studied only in P. canaliculata (Lamarck, 1822), with aerial egg-laying strategy. Its major perivitellin, ovorubin, is a reddish carotene-glycoprotein which plays multiple roles including nutrient provision, photo protection, antioxidant stabilization, proteinase inhibition and warning signal. In this work we study the egg-proteins of another aerial egg-laying Pomacea, P. scalaris. Its perivitellins were isolated by ultracentrifugation and chromatography. The major perivitellin, named scalarin, is a 380 kDa oligomer consisting of three subunits, highly glycosylated and phosphorylated and binds the carotenoid pigment astaxanthin. Structural characterization showed it is pH stable (between pH 2.0 and 8.0) and highly thermo stable (up to 80°C). Functional studies indicate it protects its carotenoid cofactor from degradation by light and oxygen suggesting one SC function is to supply carotenoids to embryos and provide egg coloration. Moreover, simulated gastrointestinal digestion determined SC was resistant to sequential proteolysis by pepsin (for 2 h at pH 2.5) and trypsin (2 h at pH 8.0). These results, together with the serine protease inhibition activity of OR, led to the hypothesis that both perivitelins could represent an antinutritive defense for Pomacea eggs, as it has been thoroughly described for protease inhibitors in plant embryo defenses against predators. This hypothesis was validated by in vivo experiments in OR (see accompanying paper). Pomacea perivitellins are thus emerging as multifunctional egg proteins involved not only in embryo nutrition but also in the biochemical adaptations to cope with the harsh conditions imposed by the aerial egg development