Liquid-Liquid Phase Separation in Membranes is a Product of Universal Material Properties and Specific Biological Functions

Many lipid membranes reversibly phase separate to form large (micron-scale) liquid domains. These systems vary widely, from simple membranes composed of only three lipid types to complex membranes of living yeast cells or giant plasma membrane vesicles. Independent of the source of the phase-separating membrane, the size, shape, and behavior of the resulting liquid domains is governed by the membrane’s material properties and the physical conditions under which it is held. For example, small domains in flaccid vesicles grow larger as membrane tension increases and as temperature decreases. Similarly, the temperature at which a membrane undergoes liquid-liquid phase separation is influenced by its lipid composition and the surfaces it touches. In simple membranes, these experimental conditions are imposed by researchers. In contrast, yeast cells actively regulate their lipid composition to achieve a particular biological outcome, namely, to maintain an offset between their growth temperature and their membrane transition temperature.