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

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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