What’s in brain lipids? Exploring the interaction of a snail pore-forming toxin with model membranes

VAZQUEZ, ROMINA; DAZA MILLONE, M. ANTONIETA; BROLA, T.; GIGLIO, M.; MATE, SABINA; HERAS, HORACIO

Congreso; LI Reunión Anual de la Sociedad Argentina de Biofísica; 2023

Perivitellin-2 (PV2) is a pore-forming toxin found in the eggs of Pomacea snails with neuro- and enterotoxic effects on mammals. It combines a member of the Membrane Attack Complex and Perforin (MACPF) family linked by a disulfide bond to a delivery lectin.Here, we studied the interaction of PV2 with model membranes, focusing on the effect of cholesterol (Chol) on protein-membrane interactions. Monolayer insertion measurements using phosphatidylcholine (PC) and PC/Chol showed higher incorporation of the toxin into Chol-containing films while surface plasmon resonance (SPR) experiments revealed increased affinity towards Chol-containing bilayers. Still, when PV2 pore-forming activity was tested in leakage experiments, no release of vesicle's content was detected in PC or PC/Chol liposomes even at high protein:lipid ratios. Considering its neurotoxic effect, the same studies were performed using rat brain lipids. Notably, PV2 produced a fast release of brain vesicle's content in a concentration-dependent manner, reaching 50% at 1:10,000 protein:lipid ratio. PV2 also showed faster incorporation kinetics into brain monolayers but only produced higher surface pressure increments at high monolayer lipid packing. SPR sensorgrams presented slower association kinetics, which must account for the overall binding-insertion-oligomerization process, with a binding affinity towards the brain system similar to PC but with a significant decrease in toxin dissociation. PV2 poreforming activity on brain lipids was further confirmed by Transmission Electron Microscopy and Atomic Force Microscopy. Both showed ~20 nm diameter pores using brain lipids that were not visible using PC/Chol membranes. These results indicate that while Chol favors the association of the toxin, it alone is insufficient to trigger pore formation. In contrast, a component from brain lipids, possibly a glycolipid for lectin delivery and toxin conformational change, is needed for PV2 activity.