title: Structure and stability of the neurotoxin PV2 from the eggs of the apple snail Pomacea canaliculata.
abstract: There is little information on the egg proteins of gastropod mollusks. Here we focus on PV2, a novel neurotoxin from snail eggs, studying its size, shape, structure, and stability, using small angle X-ray scattering (SAXS), absorption and fluorescence spectroscopy, circular dichroism, electron microscopy and partial proteolysis. Results indicate that PV2 is a compact and well folded oligomer of 130x44 A. It is an octamer of four 98 kDa heterodimers composed of 67 and 31 kDa subunits. Subunits are held together by disulfide bonds. Dimers are assembled into native PV2 by non-covalent forces. The larger subunit is more susceptible to proteolysis, indicating it is less compactly folded and/or more exposed. Quenching of tryptophan fluorescence showed a single class of tryptophyl side chains occluded in hydrophobic regions. Native structure shows loss of secondary structure (alpha+beta) at 6 M urea or 60-70 degrees C; the effects on the quaternary structure suggest an unfolding without disassembling of the protein. The 3D model of PV2 presented here is the first for an egg proteinaceous neurotoxin in animals.
authors.affiliation: Instituto de Investigaciones Físico-Químicas, Teóricas y Aplicadas (INIFTA), Universidad Nacional de La Plata-CONICET CCT-La Plata, Argentina.
authors.forename: María Victoria
authors.initials: MV
authors.lastname: Frassa
authors.forename: Marcelo
authors.initials: M
authors.lastname: Ceolín
authors.forename: Marcos S
authors.initials: MS
authors.lastname: Dreon
authors.forename: Horacio
authors.initials: H
authors.lastname: Heras
mesh_terms: D000818:Animals; D002942:Circular Dichroism; D004220:Disulfides / Q000737:chemistry; D019286:Endopeptidase K / Q000737:chemistry; D008974:Mollusca; D008978:Mollusk Venoms / Q000737:chemistry*; D009498:Neurotoxins / Q000737:chemistry*; D011487:Protein Conformation; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012542:Scattering, Radiation; D012908:Snails; D013050:Spectrometry, Fluorescence / Q000379:methods; D014364:Tryptophan / Q000737:chemistry; D014965:X-Rays
chemical_list: D004220:Disulfides; D008978:Mollusk Venoms; D009498:Neurotoxins; C550865:PV2 protein, Pomacea canaliculata; D014364:Tryptophan; D019286:Endopeptidase K