bims-fascar Biomed News
on Phase separation and cellular architecture
Issue of 2019‒12‒15
two papers selected by
Victoria Yan
Max Planck Institute of Molecular Cell Biology and Genetics

  1. Biomolecules. 2019 Dec 08. pii: E842. [Epub ahead of print]9(12):
    Uversky VN, Finkelstein AV.
      Proteins, these evolutionarily-edited biological polymers, are able to undergo intramolecular and intermolecular phase transitions. Spontaneous intramolecular phase transitions define the folding of globular proteins, whereas binding-induced, intra- and inter- molecular phase transitions play a crucial role in the functionality of many intrinsically-disordered proteins. On the other hand, intermolecular phase transitions are the behind-the-scenes players in a diverse set of macrosystemic phenomena taking place in protein solutions, such as new phase nucleation in bulk, on the interface, and on the impurities, protein crystallization, protein aggregation, the formation of amyloid fibrils, and intermolecular liquid-liquid or liquid-gel phase transitions associated with the biogenesis of membraneless organelles in the cells. This review is dedicated to the systematic analysis of the phase behavior of protein molecules and their ensembles, and provides a description of the major physical principles governing intramolecular and intermolecular phase transitions in protein solutions.
    Keywords:  amyloid fibril; coil; crystal; intrinsically-disordered protein; liquid–liquid phase separation; membraneless organelle; molten globule; phase transition; protein folding; protein structure; secondary structure
  2. Elife. 2019 Dec 09. pii: e48093. [Epub ahead of print]8
    Roper SI, Wasim L, Malinova D, Way M, Cox S, Tolar P.
      Antibody production depends on B cell internalization and presentation of antigens to helper T cells. To acquire antigens displayed by antigen-presenting cells, B cells form immune synapses and extract antigens by the mechanical activity of the acto-myosin cytoskeleton. While cytoskeleton organization driving the initial formation of the B cell synapse has been studied, how the cytoskeleton supports antigen extraction remains poorly understood. Here we show that after initial cell spreading, F-actin in synapses of primary mouse B cells and human B cell lines forms a highly dynamic pattern composed of actin foci interspersed with linear filaments and myosin IIa. The foci are generated by Arp2/3-mediated branched-actin polymerization and stochastically associate with antigen clusters to mediate internalization. However, antigen extraction also requires the activity of formins, which reside near the foci and produce the interspersed filaments. Thus, a cooperation of branched-actin foci supported by linear filaments underlies B cell mechanics during antigen extraction.
    Keywords:  cell biology; human; immunology; inflammation; mouse