PcPV2 neurotoxin from the apple snail Pomacea canaliculata eggs: A perivitellin combining perforin and lectin-like chains

DREON, M.S.; ITUARTE S,; FRASSA,V.; FERNÁNDEZ, P.E.; HERAS, H.

Santiago de Compostela

Congreso; Physiomar 12; 2012

Universidad de Santiago de Compostela

The reproductive strategy of this snail includes laying egg clutches above the water level on emergent plants and rocks. While eggs of most animals are subject to intense predation due to their high nutritional value, these aerial egg clutches have virtually no predators probably due to a complex biochemical defense system against predation. An egg protein named PcPV2 was identified as a 400 kDa oligomeric neurotoxin with lethal effect on rodents. In an attempt to understand the toxin properties that enables it to enter predator?s body, in this work we report PcPV2 primary structure, its structural stability against pH and gastrointestinal digestion aswell as its interaction with small intestine epithelia. cDNA sequencing and protein domain search of its two subunits, showed that PcPV2-31 subunit shares homology with tachylectin-like lectins while PcPV2-67 subunit displays homology with perforin-like toxins. Using a combination of small angle X-ray scattering (SAXS), fluorescence spectroscopy and simulated gastrointestinal proteolysis, PcPV2 oligomer was found to withstand proteinase digestion and displayed structural stability between pH 4.0-10.0. Loss of structure and exposure of tryptophyl residues was observed only at pH <4.0 or >10.0. PcPV2 therefore consists of a perforin-like chain covalently linked to a carbohydrate-binding-like polypeptide. This structure suggests a delivery system for the perforin is ingested by a predator, being interactions with surface oligosaccharides likely involved in the internalization of PcPV2 into the body in the intestines. Moreover, PcPV2 specifically binds to glycocalix of Caco-2 cells and small intestine enterocytes, which, coupled with its high resistance to digestion, shed light on the posible mechanisms followed by this neurotoxin to reach the central nervous system.