Disordered Motifs and Domains in Cell Control - October 11-15, 2014

Disordered Motifs and Domains in Cell Control

Tuesday Speaker Abstracts

Discerning Sequence-encoded Mechanisms of de novo Nuclear Puncta Formation by the Disordered Nephrin Intracellular Domain Chi W. Pak 1 , Anuradha Mittal 2 , Rohit V. Pappu 2 , and Michael K. Rosen 1 1 Department of Biophysics and Howard Hughes Medical Institute, University of Texas Southwestern Medical Center at Dallas, Dallas, TX, USA. 2 Department of Biomedical Engineering and Center for Biological Systems Engineering, Washington University in St. Louis, St Louis, MO, USA Phase separation leads to the formation of diverse nuclear and cytoplasmic puncta. The connection between sequence-encoded information and phase separation is poorly understood. We show that the disordered nephrin intracellular domain (NICD) , forms liquid-like nuclear puncta (nephrin puncta). We have used emerging rules for sequence-disorder relationships to quantify the impact of sequence patterns on forming nephrin puncta. These puncta require a combination of multivalent acidic motifs and hydrophobic motifs. The patterning and charge density of acidic motifs regulate phase separation leading to distinct classes of puncta. Hydrophobic motifs are also required for puncta formation. Deletion of these motifs is disruptive to puncta formation whereas the puncta are robust to sequence shuffling within the motifs. Although key proteins found in (nuclear) paraspeckle bodies colocalize to nephrin puncta, our evidence suggests that nephrin puncta are novel structures formed de novo . Our cellular measurements and computer simulations suggest that nephrin puncta, which form through liquid- liquid demixing, are likely to be driven by counterion-mediated diminution of long-range electrostatic repulsions between acidic motifs and non-specific short-range attractions mediated by hydrophobic motifs. Our studies suggest that non-specific multivalent interactions may be generally used, notably by disordered proteins, to promote the formation of known or novel phase separated cellular bodies. Further, our work suggests rules that connect sequence patterns within disordered proteins to their ability to phase separate in cells. This work was supported by grants from the NIH and Welch Foundation, and by the Howard Hughes Medical Institute.

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