Phosphatidylinositol phase behavior in symmetric and asymmetric model membranes.

Abstract

Phosphatidylinositol (PI) is a precursor to phosphoinositides (PIPs) which are important cellular signaling molecules. While the phase behavior of PI in simple model membranes has been investigated, little is known about its phase behavior in the presence of PIPs. Furthermore, the effect of divalent cations on PI/PIP interaction has not been detailed. Determining PI/PIP phase behavior is of physiological relevance because it potentially affects the lateral distribution of PIPs in cellular membranes and hence the spatiotemporal control of protein function. For diplamitoylphosphatidylinositol (DPPI) we find in pH 7.2 buffer a phase transition temperature of 43.6°C, while in the presence of Ca2+ and Mg2+ the phase transition temperature shifts to 55.8°C and 51.6°C, respectively. In addition, we investigate divalent cation dependent PI/PI(4,5)P2 phase behavior. To study PI phase behavior in asymmetric lipid bilayers, we fabricate asymmetric giant unilamellar vesicles (aGUVs) using the hemifusion method. We describe the conditions to obtain aGUVS with PI in the outer leaflet and characterize their domain morphology.