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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