| 1. |
- Glick Schiller, Nina, et al.
(author)
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Transnational regimes and migrant responses in an altered historical conjuncture
- 2018
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In: Nordic Journal of Migration Research. - : Nordic Migration Research. - 1799-649X. ; 8:4, s. 199-200
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Journal article (other academic/artistic)abstract
- Those who live their lives across the borders of nation-states as well as scholars and policy makers who research transnational lives are facing rapid alterations in mobility regimes. The articles in this special issue represent trends among transnational migration scholars who have been documenting various aspects of these changes. In order to be able to respond adequately to the transformations in the world that effect migrants and non-migrants alike, it is necessary to theorize temporality.
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| 2. |
- Kranabetter, Lorenz, et al.
(author)
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Considerable matrix shift in the electronic transitions of helium-solvated cesium dimer cation Cs2He+n
- 2019
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 21:45, s. 25362-25368
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Journal article (peer-reviewed)abstract
- We investigate the photodissociation of helium-solvated cesium dimer cations using action spectroscopy and quantum chemical calculations. The spectrum of Cs2He+ shows three distinct absorption bands into both bound and dissociative states. Upon solvation with further helium atoms, considerable shifts of the absorption bands are observed, exceeding 0.1 eV (850 cm(-1)) already for Cs2He10+, along with significant broadening. The shifts are highly sensitive to the character of the excited state. Our calculations show that helium atoms adsorb on the ends of Cs-2(+). The shifts are particularly pronounced if the excited state orbitals extend to the area occupied by the helium atoms. In this case, Pauli repulsion leads to a deformation of the excited state orbitals, resulting in the observed blue shift of the transition. Since the position of the weakly bound helium atoms is ill defined, Pauli repulsion also explains the broadening.
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| 3. |
- Lara, Patricia, et al.
(author)
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Murine astrotactins 1 and 2 have a similar membrane topology and mature via endoproteolytic cleavage catalyzed by a signal peptidase
- 2019
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In: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 294:12, s. 4538-4545
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Journal article (peer-reviewed)abstract
- Astrotactin 1 (Astn1) and Astn2 are membrane proteins that function in glial-guided migration, receptor trafficking, and synaptic plasticity in the brain as well as in planar polarity pathways in the skin. Here we used glycosylation mapping and protease protection approaches to map the topologies of mouse Astn1 and Astn2 in rough microsomal membranes and found that Astn2 has a cleaved N-terminal signal peptide, an N-terminal domain located in the lumen of the rough microsomal membranes (topologically equivalent to the extracellular surface in cells), two transmembrane helices, and a large C-terminal lumenal domain. We also found that Astn1 has the same topology as Astn2, but we did not observe any evidence of signal peptide cleavage in Astn1. Both Astn1 and Astn2 mature through endoproteolytic cleavage in the second transmembrane helix; importantly, we identified the endoprotease responsible for the maturation of Astn1 and Astn2 as the endoplasmic reticulum signal peptidase. Differences in the degree of Astn1 and Astn2 maturation possibly contribute to the higher levels of the C-terminal domain of Astn1 detected on neuronal membranes of the central nervous system. These differences may also explain the distinct cellular functions of Astn1 and Astn2, such as in membrane adhesion, receptor trafficking, and planar polarity signaling.
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| 4. |
- Mishima, Eriko, et al.
(author)
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The topogenic function of S4 promotes membrane insertion of the voltage-sensor domain in the KvAP channel
- 2016
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In: Biochemical Journal. - 0264-6021 .- 1470-8728. ; 473, s. 4361-4372
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Journal article (peer-reviewed)abstract
- Voltage-dependent K+ (K-V) channels control K+ permeability in response to shifts in the membrane potential. Voltage sensing in K-V channels is mediated by the positively charged transmembrane domain S4. The best-characterized K-V channel, KvAP, lacks the distinct hydrophilic region corresponding to the S3-S4 extracellular loop that is found in other K+ channels. In the present study, we evaluated the topogenic properties of the transmembrane regions within the voltage-sensing domain in KvAP. S3 had low membrane insertion activity, whereas S4 possessed a unique type-I signal anchor (SA-I) function, which enabled it to insert into the membrane by itself. S4 was also found to function as a stop-transfer signal for retention in the membrane. The length and structural nature of the extracellular S3-S4 loop affected the membrane insertion of S3 and S4, suggesting that S3 membrane insertion was dependent on S4. Replacement of charged residues within the transmembrane regions with residues of opposite charge revealed that Asp(72) in S2 and Glu(93) in S3 contributed to membrane insertion of S3 and S4, and increased the stability of S4 in the membrane. These results indicate that the SA-I function of S4, unique among K+ channels studied to date, promotes the insertion of S3 into the membrane, and that the charged residues essential for voltage sensing contribute to the membrane-insertion of the voltage sensor domain in KvAP.
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| 5. |
- Schiller, Nina, 1984-
(author)
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Insertion studies of model transmembrane segments into bacterial and eukaryotic membranes
- 2017
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Doctoral thesis (other academic/artistic)abstract
- Cells are encapsulated by a biological membrane in order to separate the cell interior from the surrounding environment. Different lipids and proteins compose the membrane and present a semi-permeable barrier for the diffusion of ions and molecules across the lipid bilayer. Membrane proteins also mediate the passage of signals between the interior and the exterior of the cell. To ensure the proper functioning of membrane proteins, it is essential that nascent membrane proteins are correctly integrated into the lipid bilayer to be able to fold and oligomerize. In this thesis, an engineered protein containing two natural transmembrane segments followed by an additional test segment, has been used as a model protein to study (i) sequence requirements for translocon-mediated insertion of the test segment, (ii) dynamics of nascent membrane proteins undergoing translocon-mediated insertion and (iii) to carry out an extensive mutagenesis scan to identify critical residues in the mammalian arrest peptide Xbp1 that enhances translational stalling in the ribosome. This provides a toolbox of arrest peptides with different stalling strengths that will be useful for force measurements on nascent protein chains.
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| 6. |
- Shanmuganathan, Vivekanandan, et al.
(author)
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Structural and mutational analysis of the ribosome-arresting human XBP1u
- 2019
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In: eLIFE. - 2050-084X. ; 8
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Journal article (peer-reviewed)abstract
- XBP1u, a central component of the unfolded protein response (UPR), is a mammalian protein containing a functionally critical translational arrest peptide (AP). Here, we present a 3 angstrom cryo-EM structure of the stalled human XBP1u AP. It forms a unique turn in the ribosomal exit tunnel proximal to the peptidyl transferase center where it causes a subtle distortion, thereby explaining the temporary translational arrest induced by XBP1u. During ribosomal pausing the hydrophobic region 2 (HR2) of XBP1u is recognized by SRP, but fails to efficiently gate the Sec61 translocon. An exhaustive mutagenesis scan of the XBP1u AP revealed that only 8 out of 20 mutagenized positions are optimal; in the remaining 12 positions, we identify 55 different mutations increase the level of translational arrest. Thus, the wildtype XBP1u AP induces only an intermediate level of translational arrest, allowing efficient targeting by SRP without activating the Sec61 channel.
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| 7. |
- Simonson, Oscar E., et al.
(author)
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In Vivo Effects of Mesenchymal Stromal Cells in Two Patients With Severe Acute Respiratory Distress Syndrome
- 2015
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In: Stem Cells Translational Medicine. - : Oxford University Press (OUP). - 2157-6564 .- 2157-6580. ; 4:10, s. 1199-1213
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Journal article (peer-reviewed)abstract
- Mesenchymal stromal cells (MSCs) have been investigated as a treatment for various inflammatory diseases because of their immunomodulatory and reparative properties. However, many basic questions concerning their mechanisms of action after systemic infusion remain unanswered. We performed a detailed analysis of the immunomodulatory properties and proteomic profile of MSCs systemically administered to two patients with severe refractory acute respiratory distress syndrome (ARDS) on a compassionate use basis and attempted to correlate these with in vivo anti-inflammatory actions. Both patients received 2 x 10(6) cells per kilogram, and each subsequently improved with resolution of respiratory, hemodynamic, and multiorgan failure. In parallel, a decrease was seen in multiple pulmonary and systemic markers of inflammation, including epithelial apoptosis, alveolar-capillary fluid leakage, and proinflammatory cytokines, microRNAs, and chemokines. In vitro studies of the MSCs demonstrated a broad anti-inflammatory capacity, including suppression of T-cell responses and induction of regulatory phenotypes in T cells, monocytes, and neutrophils. Some of these in vitro potency assessments correlated with, and were relevant to, the observed in vivo actions. These experiences highlight both the mechanistic information that can be gained from clinical experience and the value of correlating in vitro potency assessments with clinical effects. The findings also suggest, but do not prove, a beneficial effect of lung protective strategies using adoptively transferred MSCs in ARDS. Appropriate randomized clinical trials are required to further assess any potential clinical efficacy and investigate the effects on in vivo inflammation. STEM CELLS TRANSLATIONAL MEDICINE 2015;4:1199-1213
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| 8. |
- Stone, Tracy A., et al.
(author)
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Hydrophobic Blocks Facilitate Lipid Compatibility and Translocon Recognition of Transmembrane Protein Sequences
- 2015
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In: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 54:7, s. 1465-1473
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Journal article (peer-reviewed)abstract
- Biophysical hydrophobicity scales suggest that partitioning of a protein segment from an aqueous phase into a membrane is governed by its perceived segmental hydrophobicity but do not establish specifically (i) how the segment is identified in vivo for translocon-mediated insertion or (ii) whether the destination lipid bilayer is biochemically receptive to the inserted sequence. To examine the congruence between these dual requirements, we designed and synthesized a library of Lys-tagged peptides of a core length sufficient to span a bilayer but with varying patterns of sequence, each composed of nine Leu residues, nine Ser residues, and one (central) Trp residue. We found that peptides containing contiguous Leu residues (Leu-block peptides, e.g., LLLLLLLLLWSSSSSSSSS), in comparison to those containing discontinuous stretches of Leu residues (non-Leu-block peptides, e.g., SLSLLSLSSWSLLSLSLLS), displayed greater helicity (circular dichroism spectroscopy), traveled slower during sodium dodecyl sulfate-polyacrylamide gel electrophoresis, had longer reverse phase high-performance liquid chromatography retention times on a C-18 column, and were helical when reconstituted into 1-palmitoyl-2-oleoylglycero-3-phosphocholine liposomes, each observation indicating superior lipid compatibility when a Leu-block is present. These parameters were largely paralleled in a biological membrane insertion assay using microsomal membranes from dog pancreas endoplasmic reticulum, where we found only the Leu-block sequences successfully inserted; intriguingly, an amphipathic peptide (SLLSSLLSSWLLSSLLSSL; Leu face, Ser face) with biophysical properties similar to those of Leu-block peptides failed to insert. Our overall results identify local sequence lipid compatibility rather than average hydrophobicity as a principal determinant of transmembrane segment potential, while demonstrating that further subtleties of hydrophobic and helical patterning, such as circumferential hydrophobicity in Leu-block segments, promote translocon-mediated insertion.
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| 9. |
- Stone, Tracy A., et al.
(author)
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Hydrophobic Clusters Raise the Threshold Hydrophilicity for Insertion of Transmembrane Sequences in Vivo
- 2016
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In: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 55:40, s. 5772-5779
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Journal article (peer-reviewed)abstract
- Insertion of a nascent membrane protein segment by the translocon channel into the bilayer is naturally promoted by high segmental hydrophobicity, but its selection as a transmembrane (TM) segment is complicated by the diverse environments (aqueous vs lipidic) the protein encounters and by the fact that most TM segments contain a substantial amount (similar to 30%) of polar residues, as required for protein structural stabilization and/or function. To examine the contributions of these factors systematically, we designed and synthesized a peptide library consisting of pairs of compositionally identical, but sequentially different, peptides with 19-residue core sequences varying (i) in Leu positioning (with five or seven Leu residues clustered into a contiguous block in the middle of the segment or scrambled throughout the sequence) and (ii) in Ser content (0-6 residues). The library was analyzed by a combination of biophysical and biological techniques, including HPLC retention times, circular dichroism measurements of helicity in micelle and phospholipid bilayer media, and relative blue shifts in Trp fluorescence maxima, as well as by the extent of membrane insertion in a translocon-mediated assay using microsomal membranes from dog pancreas endoplasmic reticulum. We found that local blocks of high hydrophobicity heighten the translocon's propensity to insert moderately hydrophilic sequences, until a threshold hydrophilicity is surpassed whereby segments no longer insert even in the presence of Leu blocks. This study codifies the prerequisites of apolar/polar content and residue positioning that define nascent TM segments, illustrates the accuracy in their prediction, and highlights how a single disease-causing mutation can tip the balance toward anomaloug translocation/insertion.
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