Melittin–Phospholipase A₂ Synergism Is Mediated by Liquid–Liquid Miscibility Phase Transition in Giant Unilamellar Vesicles

The primary constituents of honeybee venom, melittin and phospholipase A 2 (PLA 2 ), display toxin synergism in which the PLA 2 activity is significantly enhanced by the presence of melittin. It has been shown previously that this is accomplished by the disruption in lipid packing, which allows PLA 2 to become processive on the membrane surface. In this work, we show that melittin is capable of driving miscibility phase transition in giant unilamellar vesicles (GUVs) and that it raises the miscibility transition temperature ( T misc ) in a concentration-dependent manner. The induced phase separation enhances the processivity of PLA 2, particularly at its boundaries, where a substantial difference in domain thickness creates a membrane discontinuity. The catalytic action of PLA 2, in response, induces changes in the membrane, rendering it more conducive to melittin binding. This, in turn, facilitates further lipid phase separation and eventual vesicle lysis. Overall, our results show that melittin has powerful membrane-altering capabilities that activate PLA 2 in various membrane contexts. More broadly, they exemplify how this biochemical system actively modulates and capitalizes on the spatial distribution of membrane lipids to efficiently achieve its objectives.