Disordered Motifs and Domains in Cell Control
Tuesday Speaker Abstracts
Disordered Linker Regions for Sorting of Transmembrane Proteins
Astri Hapsari, Annemarie Kralt, Justyna Laba, Petra Popken, Anton Steen,
Liesbeth Veenhoff
.
University of Groningen, Groningen, Netherlands.
Traffic of membrane proteins to its proper membrane compartment depends on sorting signals
encoded on the membrane proteins. We studied sorting of membrane proteins to the inner
membrane of the nuclear envelope in
Saccharomyces cerevisiae
and found that the transport of
the membrane proteins Heh1 (Src1) and Heh2 depends on a sorting signal that is composed of a
nuclear localization signal (NLS) and a long intrinsically disordered (ID) linker (Meinema et al.,
Science 2011). We proposed a transport mechanism in which the ID linker dodges into the NPC
scaffold to enable interactions inside the NPC at a distance from the membrane. We followed up
on this work and present structural, biochemical and in vivo microscopy data showing the
membrane proteins are embedded in the membrane during transport, the NLS of Heh2 has
unique properties and mutational analysis of the ID linker to probe role of flexibility and charge.
We noted that ID linkers are also present in some membrane proteins that reside in membrane
junctions or contact sites between the endoplasmic reticulum (ER) and the plasma membrane
(PM). We show that the localization at the cell periphery of two
S. cerevisiae
proteins, Ist2 and
Ssy1, depends on the presence of a plasma membrane binding domain, an ID linker region of
sufficient length and a transmembrane domain that most likely resides in the endoplasmic
reticulum. We conclude the ID regions play a relevant role in bridging adjacent heterologous
membranes.
In both targeting routes, to the inner membrane of the nuclear envelope and to the PM-ER
junctions, the role of the ID linker may be to present the sorting signal away from the crowded
membrane region and to resolve the restriction to 2D movements of membrane embedded
proteins.
Parallel Tuning of Activation and Repression in Intrinsic Disorder-Mediated Allostery
Vincent J. Hilser
1
, Jing Li
1
, Jordan T. White
1
, Harry Saavedra
1
, James O. Wrabl
1
, Hesam N.
Motlagh
1
, Kaixian Liu
1
, James L. Sowers
1
, Trina A. Schroer
1
, E. Brad Thompson
1,2
.
1
Johns Hopkins University, Baltimore, MD, USA,
2
University of Houston, Houston, TX, USA.
Intrinsically disordered proteins (IDPs) present a functional paradox because they lack stable
tertiary structure, but nonetheless play a central role in signaling. Like their structured protein
counterparts, IDPs can transmit the effects of binding an effector ligand at one site to another
functional site, a process known as allostery. Because allostery in structured proteins has
historically been interpreted in terms of propagated structural changes that are induced by
effector binding, it is not clear how IDPs, lacking such welldefined structures, can allosterically
affect function. Here we show mechanistically, using human glucocorticoid receptor (GR) as a
model, how IDPs transmit signals allosterically through a probabilistic process that originates
from the simultaneous tuning of both activating and repressing ensembles of the protein.
Moreover, GR modulates this signaling by producing translational isoforms with variable
disordered regions. These results provide a functional explanation for the prevalence of splice
sites and post-translational modufication sites within ID segments.
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