BIOPHYSICAL SOCIETY NEWSLETTER
14
JULY
2014
Subgroups
IDP
Liquid Protein Assemblies in Spatial
Organization and Ultrasensitive Signaling
in Cells
Liquid-like cellular “bodies” are light-microscop-
ically detectable structures in cells that have a
distinct composition from the surrounding cyto-
or nucleoplasm but are not enclosed by mem-
branes, e.g., P-bodies and nucleoli. The underlying
biophysical mechanism for the formation of such
bodies may be a liquid demixing phase separa-
tion. The interaction of protein molecules with
each other can under some conditions be more
favorable than with solvent, effectively concentrat-
ing the protein in a separate liquid phase, which
appears as droplets in a protein-lean solution. It is
becoming increasingly clear that some intrinsically
disordered proteins are exquisitely tuned to medi-
ate liquid demixing, reminiscent of the behavior of
synthetic polymers.
The symposium with the above title at the
2014 Annual Biophysical Society Meeting in
San Francisco, chaired by
Tanja Mittag
, St. Jude
Children’s Research Hospital, Memphis, and
Julie
Forman-Kay
,
Hospital for Sick Children, To-
ronto, highlighted the role of liquid and gel-like
protein states in the cytoplasm, the nucleus, and
the extracellular matrix. Forman-Kay discussed
microscopy and NMR studies of the liquid demix-
ing behavior of a helicase and the relationship
of this phenomenon to the formation of germ
granules.
Regis Pomes’s
, Hospital for Sick Children,
Toronto, simulations provided insight into the
biophysical basis of elastin’s intrinsic ability to
self-associate and showed that combined pro-
line and glycine content was essential for elastin’s
dynamic, disordered assemblies.
Edward Lemke
,
EMBL, Heidelberg, and his group used single
molecule fluorescence techniques to demonstrate
the highly dynamic nature of the interactions of
a FG-nucleoporin with karyopherin. Such weak
multivalent interactions may also underlie the
selectivity filter of nucleoporins and may play a
role in the formation of nucleoporin gels.
Mike
Rosen
, University of Texas Southwestern, Dallas,
described liquid demixing of proteins regulating
actin polymerization. A protein with repeats of a
folded interaction domain and a binding partner
with repeats of appropriate binding motifs are able
to demix even at low protein concentrations, giv-
ing rise to an on-/off-switch.
In all of these examples, disordered protein regions
mediate assembly and are likely essential for the
dynamic, liquid-like character. A biophysical
investigation of the molecular basis and meso-
scale properties of the aggregated states and the
spectrum of functional outcomes promises to
substantially improve our understanding of spatial
organization and biochemical regulation in cell
biology.
—Tanja Mittag
, Secretary-Treasurer
Stefan Hell
, Max Planck
Institute and Society mem-
ber since 1998, has been
awarded the Kavli Prize in
Nanoscience given by the
Norwegian Academy of
Science and Letters.
Michael Summers
, Univer-
sity of Maryland, Balti-
more County and Society
member since 2000,
has received the Ruth
Kirschstein Diversity in
Science Award from the American Society
for Biochemistry and Molecular Biology
(ASBMB).
Members in the News
