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

MATÍAS L. GIGLIO; SANTIAGO ITUARTE; HUAWEI MU; JIAN-WEN QIU; HORACIO HERAS

Cambridge

Congreso; Physiomar17; 2017

British Antarctic Survey

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 neurotoxin 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 toxicity mechanism and its role in egg defenses. PmPV2 is a multimeric protein having two subunits of 30 and 68 kDa joined by disulfide bonds. Sequence analysis of the 30-kDa subunit showed is a tachylectin-like lectin. Its predicted structure consists of a six-bladed beta propeller, a common arrangement in this family. According to bioinformatic predictions, PmPV2 displays agglutinating activity on rabbit erythrocytes, which is blocked when erythrocytes are pretreated with trypsin and by competition with aminated monosaccharides. The 68-kDa subunit belongs to the membrane attack complex/perforin (MACPF) family, a group of proteins characteristic of the mammalian immune system that perforate membranes. The predicted structure presents the typical MACPF domains, including a beta-sheet core, amphipathic 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 into a toxin, exhibiting an ?AB toxin? structure only found in bacterial and plant toxins and in animals only in its ortholog, PcPV2. In view of the structural and functional 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.