Profilin Interaction with Phosphatidylinositol (4,5)-Bisphosphate Destabilizes the Membrane of Giant Unilamellar Vesicles

Profilin, a small cytoskeletal protein, and phosphatidylinositol (4,5)-bisphosphate [PI(4,5)P-2] have been implicated in cellular events that alter the cell morphology, such as endocytosis, cell motility, and formation of the cleavage furrow during cytokinesis. Profilin has been shown to interact with PI(4,5)P-2, but the role of this interaction is still poorly understood. Using giant unilamellar vesicles (GUVs) as a simple model of the cell membrane, we investigated the interaction between profilin and PI(4,5)P-2. A number and brightness analysis demonstrated that in the absence of profilin, molar ratios of PI(4,5)P-2 above 4% result in lipid demixing and cluster formations. Furthermore, adding profilin to GUVs made with 1% PI(4,5)P-2 leads to the formation of clusters of both profilin and PI(4,5)P-2. However, due to the self-quenching of the dipyrrometheneboron difluoride-labeled PI(4,5)P-2, we were unable to determine the size of these clusters. Finally, we show that the formation of these clusters results in the destabilization and deformation of the GUV membrane.