From Intracellular Phase Transition to Synthesized Membraneless Organelles
There is currently a growing interest in biopolymer phase transitions, particularly those involving intrinsically disordered proteins/regions (IDPs/IDRs) and RNA. It has been found that intracellular liquid-liquid phase separations underlie the assembly of many membraneless organelles, including RNA/protein assemblies such as P granules, nucleoli, stress granules, and transcription factors. However, little is known about the physics of these organelles, including their internal molecular organization and feedback between their molecular and mesoscale properties. Progress on these questions has been hampered by the lack of detailed phase diagrams, which would elucidate how molecular interactions give rise to emergent droplet properties, particularly condensed-protein concentrations and their physical characteristics.
To answer these questions, we investigate the inter-molecular interaction strengths and the full binodal of a phase-separating disordered protein that induces in-vivo phase transitions, utilizing a novel microscopy, ultrafast-scanning fluorescence correlation spectroscopy. These measurements led to the recent discovery that phase-separated protein droplets have unusually low densities with large void volumes. The data demonstrate how sequence-encoded conformational fluctuations of IDRs give rise to low overlap volume fractions for driving phase separations. Using inter-molecular interactions of native membraneless organelles, we develop an optogenetic platform that permits light activation of IDR-mediated phase transitions in living cells. Inter-molecular interaction strengths are quantified and demonstrate how IDR sequences determine intracellular phase separation. These studies can elucidate not only physiological phase transitions but also for synthetic intracellular biomaterials and cellular organelle engineering applications.
Ming-Tzo (Steven) Wei is currently a Postdoctoral Research Associate in the Department of Chemical and Biological Engineering of Princeton University. He received his Ph.D. in Bioengineering from Lehigh University in 2014, M.Sc. in Biophotonics from National Yang-Ming University in Taiwan in 2006, and B.Sc. in Physics from National Dong Hwa University in Taiwan in 2004. His research interests and work include biophysics, soft matter, polymer physics, optics, biophotonics, biomaterials, bioengineering, and biomolecular & cellular engineering. Most recently his research has focused on the self-assembly of disordered proteins, bio-rheology in nonequilibrium and nonlinear living cells system, biophysics in cancer biology, colloidal electrokinetics, and the development of new microscopy.