Multifunctional perivitellins in Pomacea: Characteristic of aerial eggs?

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

Tucumán

Workshop; IV International workshop on the biology of Ampullariidae; 2010

CONSEJO NAC.DE INVEST.CIENTIF.Y TECNICAS / CTRO.CIENTIFICO TECNOL.CONICET - LA PLATA / INST.DE INVEST.BIOQUIMICAS DE LA PLATA

Ampullariids exhibit two oviposition strategies: basal clades lay eggs below the waterline while the most derived groups attach colored egg clutches to different substrates outside the water. The shift to aerial oviposition was probably a key event of Ampullariidae evolution but required physiological innovations not only in the adults but also in the eggs, as these are exposed for weeks to sunlight, high temperature, desiccation and predators. Ampullariid egg proteins, called perivitellins, have been studied only in P. canaliculata (Lamarck, 1822) and Pomacea scalaris (d’Orbigny, 1835), two species with aerial egg-laying strategy. In P. canaliculata the major perivitellin is called ovorubin, it is an oligomeric carotene-glycoprotein which plays multiple roles including nutrition, photo protection, antioxidant stabilization, protease inhibition and warning signaling. These varied functions are related to noteworthy structural features, like high thermal and chemical stability. The major perivitellin of P. scalaris, named scalarin, has been less studied. It is also a highly glycosylated oligomer, which binds and stabilizes a carotenoid pigment, providing egg coloration and antioxidants to the embryo. Although scalarin and ovorubin share some functional features, they show some biochemical differences particularly in the composition of the carbohydrate moiety. The aim of this work was to characterize the thermal and pH stability of scalarin as well as its resistance to proteolysis. We also looked further into the carbohydrate moieties of both ovorubin and scalarin. Structural characterization showed scalarin is stable in acid conditions (between pH 2.0 - 10.0) and thermo stable (up to 80°C). Functional studies indicate scalarin is resistant to simulated gastrointestinal digestion by pepsin and trypsin. Regarding the carbohydrates, we found that all subunits of both proteins have many isoforms with different isoelectric point (iP), which are probably due to the presence of sialic acid and phosphate groups. This analysis also showed that their subunits correspond to 3 polypeptides of similar molecular weight but different iP. The presence of phosphorylated serine residues may also contribute to the iP isoforms above mentioned. It is proposed that ovorubin functions as an antinutritive factor protecting P. canaliculata eggs from predation (see MS Dreon’s presentation ); the results presented here might indicate that scalarin plays a similar role in P. scalaris eggs. Pomacea perivitellins are emerging as multifunctional proteins involved in the biochemical adaptations to cope with the harsh developmental conditions of their aerial eggs.