| 1. |
- Glick Schiller, Nina
(författare)
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Beyond Methodological Ethnicity: Local and Transnational Pathways of Immigrant Incorporation
- 2008
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This paper critiques migration scholars’ reliance on the ethnic group as a unit of analysis. It argues for the importance of approaching migration studies by examining non-ethnic forms of incorporation and transnational connection. Localities of departure and settlement, especially, as place has been theorized by scholars of neoliberal urban restructuring, proves to be an important entry point for an alternative approach to migration studies. To illustrate this non-ethnic approach to migrant settlement I draw on my exploratory ethnographic research of fundamentalist Christianity as an avenue of migrant local and transnational incorporation. The research was conducted in two small-scale cities, Manchester, New Hampshire, USA and Halle/Saale, Sachsen-Anhalt, Germany.
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| 2. |
- Glick Schiller, Nina, et al.
(författare)
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Migrant Incorporation and City Scale: Towards a Theory of Locality In Migration Studies
- 2008
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The impacts of migration on the restructuring of locality remains neglected by both migration scholars and urban geographers, although the importance of global forces in structuring the flows of people, identities, subjectivities, and cultural production and consequent alterations in a time/space continuum is widely acknowledged. Yet migrants both experience and contribute to the forces of integration and fragmentation, as they participate in the rescaling of urban economies, politics and governance and the reshaping of geographies of representation. Consequently any analysis of the restructuring of urban social fabrics will be incomplete without considering the impact of migration and migrants.
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| 3. |
- Glick Schiller, Nina, et al.
(författare)
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Transnational regimes and migrant responses in an altered historical conjuncture
- 2018
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Ingår i: Nordic Journal of Migration Research. - : Nordic Migration Research. - 1799-649X. ; 8:4, s. 199-200
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)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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| 4. |
- Ismail, Nurzian, et al.
(författare)
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A biphasic pulling force acts on transmembrane helices during translocon mediated membrane integration
- 2012
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Ingår i: Nature Structural & Molecular Biology. - : Springer Science and Business Media LLC. - 1545-9993 .- 1545-9985. ; 19:10, s. 1018-1022
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Tidskriftsartikel (refereegranskat)abstract
- Membrane proteins destined for insertion into the inner membrane of bacteria or the endoplasmic reticulum membrane in eukaryotic cells are synthesized by ribosomes bound to the bacterial SecYEG or the homologous eukaryotic Sec61 translocon. During co-translational membrane integration, transmembrane alpha-helical segments in the nascent chain exit the translocon through a lateral gate that opens toward the surrounding membrane, but the mechanism of lateral exit is not well understood. In particular, little is known about how a transmembrane helix behaves when entering and exiting the translocon. Using translation-arrest peptides from bacterial SecM proteins and from the mammalian Xbp1 protein as force sensors, we show that substantial force is exerted on a transmembrane helix at two distinct points during its transit through the translocon channel, providing direct insight into the dynamics of membrane integration.
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| 5. |
- Kranabetter, Lorenz, et al.
(författare)
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Considerable matrix shift in the electronic transitions of helium-solvated cesium dimer cation Cs2He+n
- 2019
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 21:45, s. 25362-25368
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Lara, Patricia, et al.
(författare)
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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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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 294:12, s. 4538-4545
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Mishima, Eriko, et al.
(författare)
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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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Ingår i: Biochemical Journal. - 0264-6021 .- 1470-8728. ; 473, s. 4361-4372
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Tidskriftsartikel (refereegranskat)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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| 8. |
- Schiller, Nina, 1984-
(författare)
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Insertion studies of model transmembrane segments into bacterial and eukaryotic membranes
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 9. |
- Schiller, Nina, 1984-, et al.
(författare)
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Mutational analysis of the human Xbp1 translational arrest peptide and construction of arrest-enhanced variants
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Xbp1, a protein involved in the unfolded protein response, is a rare example of a mammalian protein that contains a well-defined translational arrest peptide (AP). In order to define the critical residues in the Xbp1u AP, and to search for variants with stronger arrest potency than the wildtype Xbp1u AP, we have carried out a full mutagenesis scan where each residue in the AP was replaced by the other 19 natural amino acids. We find that 10 of the 21 mutagenized positions are optimal already in the wildtype Xbp1 AP, while certain mutations in the remaining residues lead to a strong increase in the arrest potency. Xbp1 has thus evolved to induce an intermediate level of translational arrest, and versions with much stronger arrest efficiency exist. We further show Xbp1- induced translational arrest is reduced in response to increased tension in the nascent chain, making it possible to carry out studies in mammalian systems of cotranslational processes such as membrane protein assembly and protein folding by using suitable Xbp1 AP variants as “force sensors”, as has been done previously in E. coli using bacterial APs.
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| 10. |
- Shanmuganathan, Vivekanandan, et al.
(författare)
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Structural and mutational analysis of the ribosome-arresting human XBP1u
- 2019
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Ingår i: eLIFE. - 2050-084X. ; 8
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Tidskriftsartikel (refereegranskat)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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