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  • 1.
    Berntsson, Elina
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. Tallinn University of Technology, Estonia.
    Paul, Suman
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Vosough, Faraz
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Sholts, Sabrina B.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Jarvet, Jüri
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. The National Institute of Chemical Physics and Biophysics, Estonia.
    Roos, Per M.
    Barth, Andreas
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Gräslund, Astrid
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Wärmländer, Sebastian
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Lithium ions display weak interaction with amyloid-beta (Aβ) peptides and have minor effects on their aggregation2021In: Acta Biochimica Polonica, ISSN 0001-527X, E-ISSN 1734-154X, Vol. 68, no 2, p. 169-179Article in journal (Refereed)
    Abstract [en]

    Alzheimer’s disease (AD) is an incurable disease and the main cause of age-related dementia worldwide, despite decades of research. Treatment of AD with lithium (Li) has shown promising results, but the underlying mechanism is unclear. The pathological hallmark of AD brains is deposition of amyloid plaques, consisting mainly of amyloid-β (Aβ) peptides aggregated into amyloid fibrils. The plaques contain also metal ions of e.g. Cu, Fe, and Zn, and such ions are known to interact with Aβ peptides and modulate their aggregation and toxicity. The interactions between Aβ peptides and Li+ions have however not been well investigated. Here, we use a range of biophysical techniques to characterize in vitro interactions between Aβ peptides and Li+ions. We show that Li+ions display weak and non-specific interactions with Aβ peptides, and have minor effects on Aβ aggregation. These results indicate that possible beneficial effects of Li on AD pathology are not likely caused by direct interactions between Aβ peptides and Li+ions.

  • 2.
    Berntsson, Elina
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Vosough, Faraz
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Noormagi, Andra
    Padari, Kärt
    Asplund, Fanny
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Gielnik, Maciej
    Paul, Suman
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Jarvet, Jüri
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Tõugu, Vello
    Roos, Per M.
    Kozak, Maciej
    Gräslund, Astrid
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. CellPept Sweden AB, Sweden.
    Barth, Andreas
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Pooga, Margus
    Palumaa, Peep
    Wärmländer, Sebastian
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. CellPept Sweden AB, Sweden.
    Characterization of Uranyl (UO22+) Ion Binding to Amyloid Beta (Aβ) Peptides: Effects on Aβ Structure and Aggregation2023In: ACS Chemical Neuroscience, E-ISSN 1948-7193, Vol. 14, no 15, p. 2618-2633Article in journal (Refereed)
    Abstract [en]

    Uranium (U) is naturally present in ambient air, water, and soil, and depleted uranium (DU) is released into the environment via industrial and military activities. While the radiological damage from U is rather well understood, less is known about the chemical damage mechanisms, which dominate in DU. Heavy metal exposure is associated with numerous health conditions, including Alzheimer’s disease (AD), the most prevalent age-related cause of dementia. The pathological hallmark of AD is the deposition of amyloid plaques, consisting mainly of amyloid-β (Aβ) peptides aggregated into amyloid fibrils in the brain. However, the toxic species in AD are likely oligomeric Aβ aggregates. Exposure to heavy metals such as Cd, Hg, Mn, and Pb is known to increase Aβ production, and these metals bind to Aβ peptides and modulate their aggregation. The possible effects of U in AD pathology have been sparsely studied. Here, we use biophysical techniques to study in vitro interactions between Aβ peptides and uranyl ions, UO22+, of DU. We show for the first time that uranyl ions bind to Aβ peptides with affinities in the micromolar range, induce structural changes in Aβ monomers and oligomers, and inhibit Aβ fibrillization. This suggests a possible link between AD and U exposure, which could be further explored by cell, animal, and epidemiological studies. General toxic mechanisms of uranyl ions could be modulation of protein folding, misfolding, and aggregation. 

  • 3.
    Paul, Suman
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Jenistova, Adela
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Vosough, Faraz
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Berntsson, Elina
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Mörman, Cecilia
    Stockholm Univ, Dept Biochem & Biophys, Stockholm, Sweden.
    Jarvet, Jüri
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Gräslund, Astrid
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Wärmländer, Sebastian K. T. S.
    Stockholm Univ, Dept Biochem & Biophys, Stockholm, Sweden.
    Barth, Andreas
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    13C- and 15N-labeling of amyloid-β and inhibitory peptides to study their interaction via nanoscale infrared spectroscopy2023In: Communications Chemistry, E-ISSN 2399-3669, Vol. 6, no 1, article id 163Article in journal (Refereed)
    Abstract [en]

    Interactions between molecules are fundamental in biology. They occur also between amyloidogenic peptides or proteins that are associated with different amyloid diseases, which makes it important to study the mutual influence of two polypeptides on each other's properties in mixed samples. However, addressing this research question with imaging techniques faces the challenge to distinguish different polypeptides without adding artificial probes for detection. Here, we show that nanoscale infrared spectroscopy in combination with C-13, N-15-labeling solves this problem. We studied aggregated amyloid-& beta; peptide (A & beta;) and its interaction with an inhibitory peptide (NCAM1-PrP) using scattering-type scanning near-field optical microscopy. Although having similar secondary structure, labeled and unlabeled peptides could be distinguished by comparing optical phase images taken at wavenumbers characteristic for either the labeled or the unlabeled peptide. NCAM1-PrP seems to be able to associate with or to dissolve existing A & beta; fibrils because pure A & beta; fibrils were not detected after mixing. Interactions of proteins or polypeptides with different secondary structures can be studied in a mixture by nanoscale infrared spectroscopy, however, this technique remains challenging for polypeptides with similar secondary structures. Here, the authors demonstrate clear discrimination of two polypeptides from a mixture by scattering-type scanning near-field optical microscopy when one of the components is labeled with C-13- and N-15-isotopes.

  • 4. Pawlak, Krzysztof
    et al.
    Paul, Suman
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. Max-Planck-Institut für Chemische Energiekonversion, Germany.
    Liu, Cheng
    Reus, Michael
    Yang, Chunhong
    Holzwarth, Alfred R.
    On the PsbS-induced quenching in the plant major light-harvesting complex LHCII studied in proteoliposomes2020In: Photosynthesis Research, ISSN 0166-8595, E-ISSN 1573-5079, Vol. 144, no 2, p. 195-208Article in journal (Refereed)
    Abstract [en]

    Non-photochemical quenching (NPQ) in photosynthetic organisms provides the necessary photoprotection that allows them to cope with largely and quickly varying light intensities. It involves deactivation of excited states mainly at the level of the antenna complexes of photosystem II using still largely unknown molecular mechanisms. In higher plants the main contribution to NPQ is the so-called qE-quenching, which can be switched on and off in a few seconds. This quenching mechanism is affected by the low pH-induced activation of the small membrane protein PsbS which interacts with the major light-harvesting complex of photosystem II (LHCII). We are reporting here on a mechanistic study of the PsbS-induced LHCII quenching using ultrafast time-resolved chlorophyll (Chl) fluorescence. It is shown that the PsbS/LHCII interaction in reconstituted proteoliposomes induces highly effective and specific quenching of the LHCII excitation by a factor >= 20 via Chl-Chl charge-transfer (CT) state intermediates which are weakly fluorescent. Their characteristics are very broad fluorescence bands pronouncedly red-shifted from the typical unquenched LHCII fluorescence maximum. The observation of PsbS-induced Chl-Chl CT-state emission from LHCII in the reconstituted proteoliposomes is highly reminiscent of the in vivo quenching situation and also of LHCII quenching in vitro in aggregated LHCII, indicating a similar quenching mechanism in all those situations. The PsbS mutant lacking the two proton sensing Glu residues induced significant, but much smaller, quenching than wild type. Added zeaxanthin had only minor effects on the yield of quenching in the proteoliposomes. Overall our study shows that PsbS co-reconstituted with LHCII in liposomes represents an excellent in vitro model system with characteristics that are reflecting closely the in vivo qE-quenching situation.

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