Phase behaviour of disordered proteins underlying low density and high permeability of liquid organelles. Author Ming-Tzo Wei, Shana Elbaum-Garfinkle, Alex Holehouse, Carlos Chen, Marina Feric, Craig Arnold, Rodney Priestley, Rohit Pappu, Clifford Brangwynne Publication Year 2017 Type Journal Article Abstract Many intracellular membraneless organelles form via phase separation of intrinsically disordered proteins (IDPs) or regions (IDRs). These include the Caenorhabditis elegans protein LAF-1, which forms P granule-like droplets in vitro. However, the role of protein disorder in phase separation and the macromolecular organization within droplets remain elusive. Here, we utilize a novel technique, ultrafast-scanning fluorescence correlation spectroscopy, to measure the molecular interactions and full coexistence curves (binodals), which quantify the protein concentration within LAF-1 droplets. The binodals of LAF-1 and its IDR display a number of unusual features, including 'high concentration' binodal arms that correspond to remarkably dilute droplets. We find that LAF-1 and other in vitro and intracellular droplets are characterized by an effective mesh size of ∼3-8 nm, which determines the size scale at which droplet properties impact molecular diffusion and permeability. These findings reveal how specific IDPs can phase separate to form permeable, low-density (semi-dilute) liquids, whose structural features are likely to strongly impact biological function. Keywords Monte Carlo Method, Organelles, Molecular Dynamics Simulation, Permeability, Spectrometry, Fluorescence, Intrinsically Disordered Proteins, Particle Size Journal Nat Chem Volume 9 Issue 11 Pages 1118-1125 Date Published 2017 Nov ISSN Number 1755-4349 DOI 10.1038/nchem.2803 Alternate Journal Nat Chem PMCID PMC9719604 PMID 29064502 PubMedPubMed CentralGoogle ScholarBibTeXEndNote X3 XML