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Sökning: WFRF:(Persson Anders) > Umeå universitet

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1.
  • Brännström, Kristoffer, et al. (författare)
  • Ca2+ enhances Aβ polymerization rate and fibrillar stability in a dynamic manner
  • 2013
  • Ingår i: Biochemical Journal. - Portland Press. - 0264-6021. ; 450, s. 189-197
  • Tidskriftsartikel (refereegranskat)abstract
    • Identifying factors that affect the self-assembly of the amyloid-β peptide (Aβ) is of utmost importance in the quest to understand the molecular mechanisms causing Alzheimer's disease (AD). Ca2+ has previously been shown to accelerate both Aβ fibril nucleation and maturation, and a dysregulated Ca2+ homeostasis frequently correlates with development of AD. The mechanisms regarding Ca2+ binding as well as its effect on fibril kinetics are not fully understood. Using a polymerization assay we show that Ca2+ in a dynamic and reversible manner enhances both the elongation rate and fibrillar stability, where specifically the "dock and lock" phase mechanism is enhanced. Through NMR analysis we found that Ca2+ affects the fibrillar architecture. In addition, and unexpectedly, we found that Ca2+ does not bind the free Aβ monomer. This implies that Ca2+ binding requires an architecture adopted by assembled peptides, and consequently is mediated through intermolecular interactions between adjacent peptides. This gives a mechanistic explanation to the enhancing effect on fibril maturation and indicates structural similarities between prefibrillar structures and mature amyloid. Taken together we expose how Ca2+ levels affect the delicate equilibrium between the monomeric and assembled Aβ and how fluctuations in vivo may contribute to development and progression of the disease.
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2.
  • Olofsson, Anders, et al. (författare)
  • Amide solvent protection analysis demonstrates that amyloid-beta(1-40) and amyloid-beta(1-42) form different fibrillar structures under identical conditions.
  • 2007
  • Ingår i: Biochem J. - 1470-8728. ; 404:1, s. 63-70
  • Tidskriftsartikel (refereegranskat)abstract
    • AD (Alzheimer's disease) is a neurodegenerative disorder characterized by self-assembly and amyloid formation of the 39–43 residue long Ab (amyloid-b)-peptide. The most abundant species, Ab(1–40) and Ab(1–42), are both present within senile plaques, but Ab(1–42) peptides are considerably more prone to self-aggregation and are also essential for the development of AD. To understand the molecular and pathological mechanisms behind AD, a detailed knowledge of the amyloid structures of Ab-peptides is vital. In the present study we have used quenched hydrogen/deuterium-exchange NMR experiments to probe the structure of Ab(1–40) fibrils. The fibrils were prepared and analysed identically as in our previous study on Ab(1–42) fibrils, allowing a direct comparison of the two fibrillar structures. The solvent protection pattern of Ab(1–40) fibrils revealed two well-protected regions, consistent with a structural arrangement of two b-strands connected with a bend. This protection pattern partly resembles the pattern found in Ab(1–42) fibrils, but the Ab(1–40) fibrils display a significantly increased protection for the N-terminal residues Phe4–His14, suggesting that additional secondary structure is formed in this region. In contrast, the C-terminal residues Gly37–Val40 show a reduced protection that suggests a loss of secondary structure in this region and an altered filament assembly. The differences between the present study and other similar investigations suggest that subtle variations in fibril-preparation conditions may significantly affect the fibrillar architecture.
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3.
  • Olofsson, Anders, et al. (författare)
  • Quenched hydrogen/deuterium exchange NMR characterization of amyloid-β peptide aggregates formed in the presence of Cu2+ or Zn2
  • 2009
  • Ingår i: The FEBS Journal. - Wiley InterScience. - 1742-464X. ; 276:15, s. 4051-4060
  • Tidskriftsartikel (refereegranskat)abstract
    • Alzheimer's disease, a neurodegenerative disorder causing synaptic impairment and neuronal cell death, is strongly correlated with aggregation of the amyloid-β peptide (Aβ). Divalent metal ions such as Cu2+ and Zn2+ are known to significantly affect the rate of aggregation and morphology of Aβ assemblies in vitro and are also found at elevated levels within cerebral plaques in vivo. The present investigation characterized the architecture of the aggregated forms of Aβ(1–40) and Aβ(1–42) in the presence or absence of either Cu2+ or Zn2+ using quenched hydrogen/deuterium exchange combined with solution NMR spectroscopy. The NMR analyses provide a quantitative and residue-specific structural characterization of metal-induced Aβ aggregates, showing that both the peptide sequence and the type of metal ion exert an impact on the final architecture. Common features among the metal-complexed peptide aggregates are two solvent-protected regions with an intervening minimum centered at Asn27, and a solvent-accessible N-terminal region, Asp1–Lys16. Our results suggest that Aβ in complex with either Cu2+ or Zn2+ can attain an aggregation-prone β-strand–turn–β-strand motif, similar to the motif found in fibrils, but where the metal binding to the N-terminal region guides the peptide into an assembly distinctly different from the fibril form.
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4.
  • Arnqvist, Anders, et al. (författare)
  • En kunskapsbas : Sätt att organisera för att individanpassa skolgången
  • 2010
  • Ingår i: I rättan tid : Om ålder och skolstart. - Stockholm : Fritzes. - 978-91-38-23447-1 ; s. 67-87
  • Bokkapitel (övrigt vetenskapligt)abstract
    • De överväganden och förslag som redovisas i detta betänkande har tagits fram med utgångspunkt i en kunskapsbas. Kunskapsbasen består av dels översikter över aktuella forskningsresultat inom ett antal områden som har bäring på frågan om flexibel skolstart i grundskolan, dels några internationella utblickar. Vetenskapligt förankrade kunskapsöversikter har för utredningens räkning sammanställts av fyra forskare, nämligen professor Anders Arnqvist, Karlstads universitet, professor Sven Persson, Malmö högskola, fil dr Monika Vinterek, Umeå universitet och fil lic Helena Ackesjö, Linnéuniversitetet. Var och en har haft i uppdrag att inom respektive område redogöra för resultat inom svensk och internationell forskning från mitten av 1990-talet och senare. I uppdraget har ingått att uppmärksamma eventuella skillnader mellan olika elevgrupper samt effekter på både elevers kunskapsutveckling och sociala utveckling. I detta kapitel redovisas forskarnas egna sammanfattningar av forskningsöversikterna. Dessa återges i sin helhet i bilagorna 2–5. Av dem framgår också de frågeställningar och områden med bäring på flexibel skolstart som forskarna finner behov av att följa upp, utvärdera och beforska. Kunskapsbasen innehåller även en internationell utblick. I den återges hur barn på Nya Zeeland börjar skolan successivt på sin födelsedag och hur barn i England kan börja skolan vid fler tillfällen under läsåret. Lite mer utförligt redovisas dessutom diskussionen inför och införandet av rullande skolstart i Danmark och flexibel skolstart i Norge.
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5.
  • Björk, Glenn, et al. (författare)
  • A conserved modified wobble nucleoside (mcm5s2U) in lysyl-tRNA is required for viability in yeast.
  • 2007
  • Ingår i: RNA. - 1355-8382. ; 13:8, s. 1245-55
  • Tidskriftsartikel (refereegranskat)abstract
    • Transfer RNAs specific for Gln, Lys, and Glu from all organisms (except Mycoplasma) and organelles have a 2-thiouridine derivative (xm(5)s(2)U) as wobble nucleoside. These tRNAs read the A- and G-ending codons in the split codon boxes His/Gln, Asn/Lys, and Asp/Glu. In eukaryotic cytoplasmic tRNAs the conserved constituent (xm(5)-) in position 5 of uridine is 5-methoxycarbonylmethyl (mcm(5)). A protein (Tuc1p) from yeast resembling the bacterial protein TtcA, which is required for the synthesis of 2-thiocytidine in position 32 of the tRNA, was shown instead to be required for the synthesis of 2-thiouridine in the wobble position (position 34). Apparently, an ancient member of the TtcA family has evolved to thiolate U34 in tRNAs of organisms from the domains Eukarya and Archaea. Deletion of the TUC1 gene together with a deletion of the ELP3 gene, which results in the lack of the mcm(5) side chain, removes all modifications from the wobble uridine derivatives of the cytoplasmic tRNAs specific for Gln, Lys, and Glu, and is lethal to the cell. Since excess of the unmodified form of these three tRNAs rescued the double mutant elp3 tuc1, the primary function of mcm(5)s(2)U34 seems to be to improve the efficiency to read the cognate codons rather than to prevent mis-sense errors. Surprisingly, overexpression of the mcm(5)s(2)U-lacking tRNA(Lys) alone was sufficient to restore viability of the double mutant.
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6.
  • Björk, Glenn R, et al. (författare)
  • A primordial tRNA modification required for the evolution of life?
  • 2001
  • Ingår i: EMBO Journal. - 0261-4189. ; 20:1-2, s. 231-239
  • Tidskriftsartikel (refereegranskat)abstract
    • The evolution of reading frame maintenance must have been an early event, and presumably preceded the emergence of the three domains Archaea, Bacteria and Eukarya. Features evolved early in reading frame maintenance may still exist in present-day organisms. We show that one such feature may be the modified nucleoside 1-methylguanosine (m(1)G37), which prevents frameshifting and is present adjacent to and 3' of the anticodon (position 37) in the same subset of tRNAs from all organisms, including that with the smallest sequenced genome (Mycoplasma genitalium), and organelles. We have identified the genes encoding the enzyme tRNA(m(1)G37)methyltransferase from all three domains. We also show that they are orthologues, and suggest that they originated from a primordial gene. Lack of m(1)G37 severely impairs the growth of a bacterium and a eukaryote to a similar degree. Yeast tRNA(m(1)G37)methyltransferase also synthesizes 1-methylinosine and participates in the formation of the Y-base (yW). Our results suggest that m(1)G37 existed in tRNA before the divergence of the three domains, and that a tRNA(m(1)G37)methyltrans ferase is part of the minimal set of gene products required for life.
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7.
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8.
  • Brännström, Kristoffer, et al. (författare)
  • A Generic Method for Design of Oligomer-Specific Antibodies
  • 2014
  • Ingår i: PLoS ONE. - 1932-6203. ; 9:3, s. e90857
  • Tidskriftsartikel (refereegranskat)abstract
    • Antibodies that preferentially and specifically target pathological oligomeric protein and peptide assemblies, as opposed to their monomeric and amyloid counterparts, provide therapeutic and diagnostic opportunities for protein misfolding diseases. Unfortunately, the molecular properties associated with oligomer-specific antibodies are not well understood, and this limits targeted design and development. We present here a generic method that enables the design and optimisation of oligomer-specific antibodies. The method takes a two-step approach where discrimination between oligomers and fibrils is first accomplished through identification of cryptic epitopes exclusively buried within the structure of the fibrillar form. The second step discriminates between monomers and oligomers based on differences in avidity. We show here that a simple divalent mode of interaction, as within e. g. the IgG isotype, can increase the binding strength of the antibody up to 1500 times compared to its monovalent counterpart. We expose how the ability to bind oligomers is affected by the monovalent affinity and the turnover rate of the binding and, importantly, also how oligomer specificity is only valid within a specific concentration range. We provide an example of the method by creating and characterising a spectrum of different monoclonal antibodies against both the A beta peptide and alpha-synuclein that are associated with Alzheimer's and Parkinson's diseases, respectively. The approach is however generic, does not require identification of oligomer-specific architectures, and is, in essence, applicable to all polypeptides that form oligomeric and fibrillar assemblies.
9.
  • Burza, Matthias, et al. (författare)
  • Hollow microspheres as targets for staged laser-driven proton acceleration
  • 2011
  • Ingår i: New Journal of Physics. - Institute of Physics Publishing (IOPP). - 1367-2630. ; 13, s. 013030
  • Tidskriftsartikel (refereegranskat)abstract
    • A coated hollow core microsphere is introduced as a novel targetin ultra-intense laser–matter interaction experiments. In particular, it facilitates staged laser-driven proton acceleration by combining conventional target normal sheath acceleration (TNSA), power recycling of hot laterally spreading electrons and staging in a very simple and cheap target geometry. During TNSA of protons from one area of the sphere surface, laterally spreading hot electrons form a charge wave. Due to the spherical geometry, this wave refocuses on the opposite side of the sphere, where an opening has been laser micromachined.This leads to a strong transient charge separation field being set up there, which can post-accelerate those TNSA protons passing through the hole at the right time. Experimentally, the feasibility of using such targets is demonstrated. A redistribution is encountered in the experimental proton energy spectra, as predicted by particle-in-cell simulations and attributed to transient fields set up by oscillating currents on the sphere surface.
10.
  • Burza, Matthias, et al. (författare)
  • Laser wakefield acceleration using wire produced double density ramps
  • 2013
  • Ingår i: Physical Review Special Topics - Accelerators and Beams. - American Physical Society. - 1098-4402. ; 16:1, s. 011301
  • Tidskriftsartikel (refereegranskat)abstract
    • A novel approach to implement and control electron injection into the accelerating phase of a laser wakefield accelerator is presented. It utilizes a wire, which is introduced into the flow of a supersonic gas jet creating shock waves and three regions of differing plasma electron density. If tailored appropriately, the laser plasma interaction takes place in three stages: Laser self-compression, electron injection, and acceleration in the second plasma wave period. Compared to self-injection by wave breaking of a nonlinear plasma wave in a constant density plasma, this scheme increases beam charge by up to 1 order of magnitude in the quasimonoenergetic regime. Electron acceleration in the second plasma wave period reduces electron beam divergence by approximate to 25%, and the localized injection at the density downramps results in spectra with less than a few percent relative spread. DOI: 10.1103/PhysRevSTAB.16.011301
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