| 1. |
- Boy, M., et al.
(författare)
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Interactions between the atmosphere, cryosphere, and ecosystems at northern high latitudes
- 2019
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 19:3, s. 2015-2061
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Tidskriftsartikel (refereegranskat)abstract
- The Nordic Centre of Excellence CRAICC (Cryosphere-Atmosphere Interactions in a Changing Arctic Climate), funded by NordForsk in the years 2011-2016, is the largest joint Nordic research and innovation initiative to date, aiming to strengthen research and innovation regarding climate change issues in the Nordic region. CRAICC gathered more than 100 scientists from all Nordic countries in a virtual centre with the objectives of identifying and quantifying the major processes controlling Arctic warming and related feedback mechanisms, outlining strategies to mitigate Arctic warming, and developing Nordic Earth system modelling with a focus on short-lived climate forcers (SLCFs), including natural and anthropogenic aerosols. The outcome of CRAICC is reflected in more than 150 peer-reviewed scientific publications, most of which are in the CRAICC special issue of the journal Atmospheric Chemistry and Physics. This paper presents an overview of the main scientific topics investigated in the centre and provides the reader with a state-of-the-art comprehensive summary of what has been achieved in CRAICC with links to the particular publications for further detail. Faced with a vast amount of scientific discovery, we do not claim to completely summarize the results from CRAICC within this paper, but rather concentrate here on the main results which are related to feedback loops in climate change-cryosphere interactions that affect Arctic amplification.
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| 2. |
- Liebau, Jobst, et al.
(författare)
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Fast-tumbling bicelles constructed from native Escherichia coli lipids
- 2016
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Ingår i: Biochimica et Biophysica Acta - Biomembranes. - : Elsevier BV. - 1879-2642 .- 0005-2736. ; 1858:9, s. 2097-2105
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Tidskriftsartikel (refereegranskat)abstract
- Solution-state NMR requires small membrane mimetic systems to allow for acquiring high-resolution data. At the same time these mimetics should faithfully mimic biological membranes. Here we characterized two novel fast-tumbling bicelle systems with lipids from two Escherichia coli strains. While strain 1 (AD93WT) contains a characteristic E. coli lipid composition, strain 2 (AD93-PE) is not capable of synthesizing the most abundant lipid in E. coli, phosphatidylethanolamine. The lipid and acyl chain compositions were characterized by P-31 and C-13 NMR. Depending on growth temperature and phase, the lipid composition varies substantially, which means that the bicelle composition can be tuned by using lipids from cells grown at different temperatures and growth phases. The hydrodynamic radii of the bicelles were determined from translational diffusion coefficients and NMR spin relaxation was measured to investigate lipid properties in the bicelles. We find that the lipid dynamics are unaffected by variations in lipid composition, suggesting that the bilayer is in a fluid phase under all conditions investigated here. Backbone glycerol carbons are the most rigid positions in all lipids, while head-group carbons and the first carbons of the acyl chain are somewhat more flexible. The flexibility increases down the acyl chain to almost unrestricted motion at its end. Carbons in double bonds and cyclopropane moieties are substantially restricted in their motional freedom. The bicelle systems characterized here are thus found to faithfully mimic E. coli inner membranes and are therefore useful for membrane interaction studies of proteins with E. coli inner membranes by solution-state NMR. (C) 2016 Elsevier B.V. All rights reserved.
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| 3. |
- Liebau, Jobst, et al.
(författare)
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Membrane Interaction of the Glycosyltransferase WaaG
- 2015
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Ingår i: Biophysical Journal. - : Elsevier BV. - 0006-3495 .- 1542-0086. ; 109:3, s. 552-563
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Tidskriftsartikel (refereegranskat)abstract
- The glycosyltransferase WaaG is involved in the synthesis of lipopolysaccharides that constitute the outer leaflet of the outer membrane in Gram-negative bacteria such as Escherichia coli. WaaG has been identified as a potential antibiotic target, and inhibitor scaffolds have previously been investigated. WaaG is located at the cytosolic side of the inner membrane, where the enzyme catalyzes the transfer of the first outer-core glucose to the inner core of nascent lipopolysaccharides. Here, we characterized the binding of WaaG to membrane models designed to mimic the inner membrane of E. coli. Based on the crystal structure, we identified an exposed and largely a-helical 30-residue sequence, with a net positive charge and several aromatic amino acids, as a putative membrane-interacting region of WaaG (MIR-WaaG). We studied the peptide corresponding to this sequence, along with its bilayer interactions, using circular dichroism, fluorescence quenching, fluorescence anisotropy, and NMR. In the presence of dodecylphosphocholine, MIR-WaaG was observed to adopt a three-dimensional structure remarkably similar to the segment in the crystal structure. We found that the membrane interaction of WaaG is conferred at least in part by MIR-WaaG and that electrostatic interactions play a key role in binding. Moreover, we propose a mechanism of anchoring WaaG to the inner membrane of E. coli, where the central part of MIR-WaaG inserts into one leaflet of the bilayer. In this model, electrostatic interactions as well as surface-exposed Tyr residues bind WaaG to the membrane.
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| 4. |
- Mukka, Sebastian, et al.
(författare)
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External Validity of the HOPE-Trial Hemiarthroplasty Compared with Total Hip Arthroplasty for Displaced Femoral Neck Fractures in Octogenarians
- 2019
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Ingår i: JBJS Open Access. - : JBJS. - 2472-7245. ; 4:2, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- Background: Randomized controlled trials (RCTs) are the most reliable way of evaluating the effect of new treatments by comparing them with previously accepted treatment regimens. The results obtained from an RCT are extrapolated from the study environment to the general health care system. The ability to do so is called external validity. We sought to evaluate the external validity of an RCT comparing the results of total hip arthroplasty with those of hemiarthroplasty for the treatment of displaced femoral neck fractures in patients ≥80 years of age.Methods: This prospective, single-center cohort study included 183 patients ≥80 years of age who had a displaced femoral neck fracture. All patients were screened according to the inclusion and exclusion criteria for an RCT comparing total hip arthroplasty and hemiarthroplasty. The population for this study consisted of patients who gave their informed consent and were randomized into the RCT (consenting group, 120 patients) as well as those who declined to give their consent to participate (non-consenting group, 63 patients). The outcome measurements were mortality, complications, and patient-reported outcome measures. Follow-up was carried out postoperatively with use of a mailed survey that included patient-reported outcome questionnaires.Results: We found a statistically significant and clinically relevant difference between the groups, with the non-consenting group having a higher risk of death compared with the consenting group. (hazard ratio, 4.6; 95% confidence interval, 1.9 to 11.1). No differences were found between the groups in terms of patient-reported outcome measures or surgical complications.Conclusions: This cohort study indicates a higher mortality rate but comparable hip function and quality of life among eligible non-consenters as compared with eligible consenters when evaluating the external validity of an RCT in patients ≥80 years of age with femoral neck fracture.Level of Evidence: Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.
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| 5. |
- Nordgren, Niklas, et al.
(författare)
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Oncogene induced stiffening of living cells
- 2015
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Ingår i: Abstracts of Papers of the American Chemical Society. - : AMER CHEMICAL SOC. - 0065-7727. ; 249
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 6. |
- Ovaskainen, Louise, et al.
(författare)
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The effect of different wear on superhydrophobic wax coatings
- 2017
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Ingår i: Nordic Pulp & Paper Research Journal. - : De Gruyter Open Ltd. - 0283-2631 .- 2000-0669. ; 32:2, s. 195-203
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Tidskriftsartikel (refereegranskat)abstract
- Wear resistance of superhydrophobic coatings made by spraying a crystallizing wax from supercritical carbon dioxide solutions was evaluated using several methods. Scratch tests were performed using a tip in contact with the surface using atomic force microscope (AFM). Compression tests were performed by applying different loads on a rubber stamp placed on the surface. Frictional wear was evaluated by stroking an index finger over the surfaces while measuring applied load and friction. The wetting properties of the coatings were subsequently evaluated as advancing and receding water contact angles, superhydrophobic sliding resistance according to a recently developed method and surface roughness, coating morphology was studied using scanning electron microscopy and optical profilometry. Scratching with tip of an AFM cantilever with a force of 12 nN removed major fraction of the wax coating from underlying silica substrate whereas subjecting the surfaces to a compressive load up to 59 kPa did not significantly influence the superhydrophobicity of the coatings. Frictional wear measurements indicate that superhydrophobic properties were immediately lost after pressing and moving a finger over the coating, as movement of the finger destroyed the fine surface structure. Nevertheless, the surfaces could withstand up to 200000 falling water drops without losing their superhydrophobicity. © 2017 De Gruyter Open Ltd. All rights reserved.
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| 7. |
- Pettersson, Pontus, et al.
(författare)
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Structure and dynamics of plant TatA in micelles and lipid bilayers studied by solution NMR
- 2018
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Ingår i: The FEBS Journal. - : Wiley. - 1742-464X .- 1742-4658. ; 285:10, s. 1886-1906
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Tidskriftsartikel (refereegranskat)abstract
- The twin-arginine translocase (Tat) transports folded proteins across the cytoplasmic membrane of prokaryotes and the thylakoid membrane of plant chloroplasts. In Gram-negative bacteria and chloroplasts, the translocon consists of three subunits, TatA, TatB, and TatC, of which TatA is responsible for the actual membrane translocation of the substrate. Herein we report on the structure, dynamics, and lipid interactions of a fully functional C-terminally truncated core TatA' from Arabidopsisthaliana using solution-state NMR. Our results show that TatA consists of a short N-terminal transmembrane helix (TMH), a short connecting linker (hinge) and a long region with propensity to form an amphiphilic helix (APH). The dynamics of TatA were characterized using N-15 relaxation NMR in combination with model-free analysis. The TMH has order parameters characteristic of a well-structured helix, the hinge is somewhat less rigid, while the APH has lower order parameters indicating structural flexibility. The TMH is short with a surprisingly low protection from solvent, and only the first part of the APH is protected to some extent. In order to uncover possible differences in TatA's structure and dynamics in detergent compared to in a lipid bilayer, fast-tumbling bicelles and large unilamellar vesicles were used. Results indicate that the helicity of TatA increases in both the TMH and APH in the presence of lipids, and that the N-terminal part of the TMH is significantly more rigid. The results indicate that plant TatA has a significant structural plasticity and a capability to adapt to local environments.
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| 8. |
- Pettersson, Pontus, 1987-
(författare)
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Structure, dynamics and lipid interaction of membrane-associated proteins
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A research topic within the field of molecular biophysics is the structure-function relationship of proteins. Membrane proteins are a large, diverse group of biological macromolecules that perform many different and essential functions for the cell. Despite the abundance and importance of membrane proteins, high-resolution 3D structures from this class of proteins are underrepresented among all yet determined structures. The limited amount of data for membrane proteins hints about the higher difficulty associated with studies of this group of molecules. The determination of an atomic resolution structure is often a long process in which several obstacles need to be overcome, in particular for membrane proteins.Solution-state nuclear magnetic resonance (NMR) is a powerful measurement technique that can provide high-resolution data on the structure and dynamics of biological macromolecules, and is suitable for studies of small, dynamic membrane proteins. However, even with solution-state NMR, the membrane proteins need to be investigated in environments that are sometimes severely compromising for the protein’s native structure and function. In order to evaluate the biological significance of results obtained under such artificial conditions, supporting data from experiments in more realistic membrane models, obtained using NMR and other biophysical methods, is of great importance.The work presented in this thesis concerns studies of four membrane proteins: WaaG, Rcf1, Rcf2 and TatA. These proteins have very different characteristics in terms of their sizes and expected membrane interactions, and were accordingly found to be differently affected by the model membranes in which they were studied. Our results illustrate both the current possibilities and limitations of solution-state NMR for studying membrane proteins, and highlight the benefits of an approach where several membrane mimicking systems and measurements techniques are used in combination to arrive at correct conclusions on the properties of proteins.
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| 9. |
- Zhou, Shu, et al.
(författare)
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NMR Study of Rcf2 Reveals an Unusual Dimeric Topology in Detergent Micelles
- 2018
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Ingår i: ChemBioChem. - : Wiley. - 1439-4227 .- 1439-7633. ; 19:5, s. 444-447
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Tidskriftsartikel (refereegranskat)abstract
- The Saccharomyces cerevisiae mitochondrial respiratory supercomplex factor2 (Rcf2) plays a role in assembly of supercomplexes composed of cytochromebc(1) (complexIII) and cytochromec oxidase (complexIV). We expressed the Rcf2 protein in Escherichia coli, refolded it, and reconstituted it into dodecylphosphocholine (DPC) micelles. The structural properties of Rcf2 were studied by solution NMR, and near complete backbone assignment of Rcf2 was achieved. The secondary structure of Rcf2 contains seven helices, of which five are putative transmembrane (TM) helices, including, unexpectedly, a region formed by a charged 20-residue helix at the Cterminus. Further studies demonstrated that Rcf2 forms a dimer, and the charged TM helix is involved in this dimer formation. Our results provide a basis for understanding the role of this assembly/regulatory factor in supercomplex formation and function.
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| 10. |
- Zhou, Shu, et al.
(författare)
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Solution NMR structure of yeast Rcf1, a protein involved in respiratory supercomplex formation
- 2018
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 115:12, s. 3048-3053
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Tidskriftsartikel (refereegranskat)abstract
- The Saccharomyces cerevisiae respiratory supercomplex factor 1 (Rcf1) protein is located in the mitochondrial inner membrane where it is involved in formation of supercomplexes composed of respiratory complexes III and IV. We report the solution structure of Rcf1, which forms a dimer in dodecylphosphocholine (DPC) micelles, where each monomer consists of a bundle of five transmembrane (TM) helices and a short flexible soluble helix (SH). Three TM helices are unusually charged and provide the dimerization interface consisting of 10 putative salt bridges, defining a charge zipper motif. The dimer structure is supported by molecular dynamics (MD) simulations in DPC, although the simulations show a more dynamic dimer interface than the NMR data. Furthermore, CD and NMR data indicate that Rcf1 undergoes a structural change when reconstituted in liposomes, which is supported by MD data, suggesting that the dimer structure is unstable in a planar membrane environment. Collectively, these data indicate a dynamic monomer-dimer equilibrium. Furthermore, the Rcf1 dimer interacts with cytochrome c, suggesting a role as an electron-transfer bridge between complexes III and IV. The Rcf1 structure will help in understanding its functional roles at a molecular level.
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