The Role of Protein-Protein Interactions and Phase Separation in Biophysics

Liquid-liquid phase separation is a form of polymer chemistry, recently found to be particularly relevant to cell biology, that involves the de-mixing of enclosed molecules into a dense phase and a depleted phase [1]. This results in the formation of various membrane-less organelles, such as P bodies and stress granules. Summarizing several studies of various membrane-less organelles, three basic principles underlie all compartments [2]: first, membrane-less organelles arise from the phase separation of proteins or proteins and nucleic acids from the surrounding milieu; second, membrane-less organelles remain in a liquid-like state but have properties distinct from those of the surrounding milieu; and third, proteins exchange with membrane-less organelles in the span of seconds instead of minutes/hours or longer, as generally occurs for subunits of stable complexes. The dynamic and liquid-like properties of membrane-less organelles present unique opportunities to control the biochemical environment of the cell that are distinct from those provided by canonical macromolecular complexes [3].