| 1. |
- Norlin, Nils, et al.
(author)
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Aggregation and fibril morphology of the Arctic mutation of Alzheimer's Aβ peptide by CD, TEM, STEM and in situ AFM
- 2012
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In: Journal of Structural Biology. - San Diego, CA, USA : Academic Press. - 1047-8477 .- 1095-8657. ; 180:1, s. 174-189
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Journal article (peer-reviewed)abstract
- Morphology of aggregation intermediates, polymorphism of amyloid fibrils and aggregation kinetics of the "Arctic" mutant of the Alzheimer's amyloid β-peptide, Aβ((1-40))(E22G), in a physiologically relevant Tris buffer (pH 7.4) were thoroughly explored in comparison with the human wild type Alzheimer's amyloid peptide, wt-Aβ((1-40)), using both in situ atomic force and electron microscopy, circular dichroism and thioflavin T fluorescence assays. For arc-Aβ((1-40)) at the end of the 'lag'-period of fibrillization an abrupt appearance of ∼3nm size 'spherical aggregates' with a homogeneous morphology, was identified. Then, the aggregation proceeds with a rapid growth of amyloid fibrils with a variety of morphologies, while the spherical aggregates eventually disappeared during in situ measurements. Arc-Aβ((1-40)) was also shown to form fibrils at much lower concentrations than wt-Aβ((1-40)): ⩽2.5μM and 12.5μM, respectively. Moreover, at the same concentration, 50μM, the aggregation process proceeds more rapidly for arc-Aβ((1-40)): the first amyloid fibrils were observed after c.a. 72h from the onset of incubation as compared to approximately 7days for wt-Aβ((1-40)). Amyloid fibrils of arc-Aβ((1-40)) exhibit a large variety of polymorphs, at least five, both coiled and non-coiled distinct fibril structures were recognized by AFM, while at least four types of arc-Aβ((1-40)) fibrils were identified by TEM and STEM and their mass-per-length statistics were collected suggesting supramolecular structures with two, four and six β-sheet laminae. Our results suggest a pathway of fibrillogenesis for full-length Alzheimer's peptides with small and structurally ordered transient spherical aggregates as on-pathway immediate precursors of amyloid fibrils.
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| 2. |
- Filippov, Andrei, et al.
(author)
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Aggregation of amyloid Aβ(1-40) peptide in perdeuterated 2,2,2-trifluoroethanol caused by ultrasound sonication
- 2010
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In: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 48:6, s. 427-434
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Journal article (peer-reviewed)abstract
- Ultrasound sonication of protein and peptide solutions is routinely used in biochemical, biophysical, pharmaceutical and medical sciences to facilitate and accelerate dissolution of macromolecules in both aqueous and organic solvents. However, the impact of ultrasound waves on folding/unfolding of treated proteins, in particular, on aggregation kinetics of amyloidogenic peptides and proteins is not understood. In this work, effects of ultrasound sonication on the misfolding and aggregation behavior of the Alzheimer's Aβ(1–40)-peptide is studied by pulsed-field gradient (PFG) spin–echo diffusion NMR and UV circular dichroism (CD) spectroscopy. Upon simple dissolution of Aβ(1–40) in perdeuterated trifluoroethanol, CF3-CD2-OD (TFE-d3), the peptide is present in the solution as a stable monomer adopting α-helical secondary structural motifs. The self-diffusion coefficient of Aβ(1–40) monomers in TFE-d3 was measured as 1.35 × 10−10 m2 s−1, reflecting its monomeric character. However, upon ultrasonic sonication for less than 5 min, considerable populations of Aβ molecules (ca 40%) form large aggregates as reflected in diffusion coefficients smaller than 4.0 × 10−13 m2 s−1. Sonication for longer times (up to 40 min in total) effectively reduces the fraction of these aggregates in 1H PFG NMR spectra to ca 25%. Additionally, absorption below 230 nm increased significantly upon sonication treatment, an observation, which also clearly confirms the ongoing aggregation process of Aβ(1–40) in TFE-d3. Surprisingly, upon ultrasound sonication only small changes in the peptide secondary structure were detected by CD: the peptide molecules mainly adopt α-helical motifs in both monomers and aggregates formed upon sonication.
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| 3. |
- Filippov, A. V., et al.
(author)
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Effect of freezing on amyloid peptide aggregation and self-diffusion in an aqueous solution
- 2008
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In: Colloid Journal of the Russian Academy of Science. - 1061-933X .- 1608-3067. ; 70:4, s. 501-506
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Journal article (peer-reviewed)abstract
- Pulsed-field gradient 1H NMR is employed to investigate the self-diffusion of amyloid Aβ-peptide in an aqueous buffer solution (pH 7.44) with a protein concentration of 50 μmol at 20°C. The self-diffusion coefficient of the peptide in a freshly prepared solution corresponds to its monomeric form. The storage of the solution at 24°C causes part of the peptide molecules to form amyloid aggregates as soon as over 48 h. However, the 1H NMR echo signal typical of aggregated molecules is not observed because of their dense packing in the aggregates and a large mass of the latter. A freezing-fusion of the solution after the aggregation does not cause changes in the self-diffusion coefficients of the peptide. After a peptide solution free of amyloid aggregates is subjected to a freezing-fusion cycle, part of the peptide molecules also remains in the monomeric form in the solution, while another part forms amyloid aggregates, with a portion of the aggregated peptide molecules retaining a high rotational mobility with virtually absolute absence of a translational mobility. The results obtained are interpreted in terms of the formation of "porous aggregates" of amyloid fibrils, with "pores" having sizes comparable with those of peptide molecules, though, being larger than water molecules. Peptide molecules, which do not form fibrils, are captured in the pores. Temperature regime is shown to be of importance for the aggregation of amyloid peptides. In particular, freezing, which is traditionally considered to be a method for the prevention from or temporary interruption of aggregation, may itself lead to the formation of amorphous amyloid aggregates, which remain preserved in solutions after their unfreezing.
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| 4. |
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| 5. |
- Sharutin, V. V., et al.
(author)
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Tetraphenyl- and tetratolylantimony complexes with N,N-dialkyldithiocarbamate ligands : synthesis, X-ray diffraction analysis, and 13C and 15N CP/MAS NMR studies
- 2006
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In: Russian journal of coordination chemistry. - 1070-3284 .- 1608-3318. ; 32:3:6, s. 87-396
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Journal article (peer-reviewed)abstract
- Crystalline tetraphenylantimony and tetratolylantimony complexes with N,N-dialkyldithiocarbamate ligands [Sb(C6H5)4(S2CNR2)] (R = CH3, C2H5, and C3H7 and R2 = (CH2)6) were synthesized by ligand exchange reactions and studied by 13C and 15N CP/MAS NMR spectroscopy. X-ray diffraction analysis revealed that the complex [Sb(n-CH3-C6H4)4{S2CN(C3H7)2}] exists as the single molecular form, while [Sb(C6H5)4{S2CN(CH2)6}] exists as two molecular conformers. The 13C and 15N signals were assigned to the positions of the atoms in the isomeric structures [Sb(C6H5)4{S2CN(CH2)6}] in terms of different degrees of double bonding in the formally single =N-C(S)S-bond.
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