Structure-function analysis of the PmPV2 neurotoxin from the eggs of the apple snail Pomacea maculata

ITUARTE, S; HERAS, H; MU, H.; GIGLIO, ML; QIU, JW

Cambridge

Congreso; Physiomar; 2017

Apple snails from the Pomacea genus are freshwater amphibious snails characterized by aerial oviposition, in which adult females venture outside the water and deposit their eggs in conspicuously colored egg masses on hard surfaces. This reproductive strategy exposes the eggs to harsh conditions and terrestrial predators. However, these eggs are ignored by most predators, which is explained by the presence of a complex defense system including multifunctional proteins. Among them is the toxin PV2 from P. canaliculata (PcPV2) and P. maculata (PmPV2) eggs. The aim of the present work was to study the molecular and functional features of PmPV2 to better understand its mechanism of toxic action and role in egg defenses. PmPV2 is a multimeric protein composed of two subunits of 30 and 68 kDa joined by disulfide bonds. Sequence analysis of the 30-kDa subunit showed it is related to the tachylectin family of lectins. Its predicted structure consists of a six-bladed beta propeller, a common arrangement in this family. In accordance with this, PmPV2 shows agglutinating activity on rabbit erythrocytes, which is blocked either when erythrocytes are pretreated with trypsin or by competition with aminated monosaccharides. The 68-kDa subunit belongs to the MACPF family, a group of proteins characteristic of the mammalian immune system that perforate membranes. The predicted structure of this subunit presents the typical MACPF domains, including a beta-sheet core, the amphipathic transmembrane helixes related with membrane insertion and a Cys-rich Ct domain generally related with recognition and binding to membranes. In this respect, PmPV2 showed strong affinity to cholesterol, a characteristic of MACPF proteins associated with its protein-membrane interaction in the pore formation process. In conclusion, PmPV2 combines two proteins from the immune system in a toxin, exhibiting an ?AB toxin? structure found in bacterial and plant toxins. In view of the structural features, we propose that PmPV2 lectin subunit would act as the delivery domain recognizing and binding cell membranes, while the MACPF subunit, presumably would act as a pore-forming toxin