Effects of Pore-forming toxins (PFTs) on oxidized model membranes represented by Giant Unilamellar Vesicles (GUVs)

Abstract

Sticholysin I (St1) and II (St2) are polypeptides isolated from the Caribbean sea anemone Stichodactyla Helianthus, with a molecular mass of 19401 and 19290 Da, with hemolytic and pore-forming properties in membranes (LANIO et al., 2000). It has been previously determined that the activity of membrane pore formation is related to the N-terminal insertion in the bilayer and lipid phase coexistence must play a role too (ROS et al., 2013). As PFTs, both toxins are considered to have potential appliance in parasitic and tumor diseases (MARTÍNEZ et al., 2007). In this work, we have investigated GUVs composed of nonoxidized POPC and POPC hydroperoxide (POPC-OOH) interacting with ST1 and ST2 by optical microscopy. The results did not reveal a significant PFT-membrane interaction such that no membrane destabilization was observed over incubation time of 20 min. On the other hand, when GUVs were made of mixtures of POPC or POPC-OOH and Sphingomyellin (SM), optical contrast fading was noticed indicating an increase in lipid bilayer permeability due to pore formation. Of note, neither micron-sized pores were observed nor membrane disruption. Further, the results also pointed out vesicles composed of oxidized lipids and SM have a much faster pore forming capacity. Therefore, our results thus suggest that membranes containing -OOH and SM promote the insertion of toxins due to their great fluidity, facilitating the insertion of the TFPs and their differentiation, leading to the formation of pores.