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- Abelein, Axel, 1985-
(author)
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Modulation of Alzheimer's amyloid β peptide self-assembly : Insights into molecular mechanisms of peptide aggregation associated with Alzheimer's disease
- 2015
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Doctoral thesis (other academic/artistic)abstract
- Misfolding of proteins and peptides is closely linked to several neurodegenerative disorders, among them Alzheimer's disease (AD), the most prominent example of brain diseases. The self-assembly of the amyloid β peptide (Aβ) into amyloid fibrils is one histologic hallmark of AD. A detailed knowledge about the underlying mechanism(s) of Aβ aggregation is crucial for advances toward a fundamental understanding of the disease, which may promote the search for and design of efficient therapeutics. The work presented in this thesis deals with modulation of the aggregation process by various compounds, i.e. small organic molecules (e.g. lacmoid and Congo red), surfactants and metal ions. These results provide insight into the molecular mechanism of modulator interactions and interference with Aβ and its aggregation pathways. Applying a combination of kinetic and dynamic studies as well as structural investigations we characterized the molecular interactions between Aβ and aggregation modulators in terms of microscopic rate constants, conformational preferences and thermodynamics. An important conclusion is that these modulators form highly dynamic complexes with Aβ, with life-times on the timescale of milliseconds. Despite the similar exchange dynamics, the effect on peptide aggregation is modulator-specific and fibril formation can be accelerated, retarded or inhibited by their interactions. In summary, Aβ self-assembly is governed by microscopic kinetic and dynamic processes that can be altered by aggregation modulators. Further elucidation of these mechanisms is beneficial for the understanding and therapeutic intervention of amyloid diseases.
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| 2. |
- Bárány-Wallje, Elsa, 1979-
(author)
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Biophysical studies of cell-penetrating peptides and of the RNR inhibitor Sml1
- 2008
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Doctoral thesis (other academic/artistic)abstract
- Several short peptides, so called cell-penetrating peptides, have the capability to transport large hydrophilic cargos through the cell membrane. The objective is to use these peptides as drug carriers and thereby enhance the uptake of drugs into cells.Three different cell-penetrating peptides are characterized in this thesis. Structure and dynamics of transportan when bound to phospholipid bicelles was determined using NMR. The hydrophobic peptide transportan and its deletion analogue Tp10 both bind to lipid head-group region of the membrane as amphipathic α-helices (papers I & II) and they were found to cause leakage in vesicles (paper IV). The membrane disturbing effect is probably part of how these peptides are translocated through the cell membrane, but also an explanation to why these peptides are found to be toxic in vivo. The high degree of toxicity limits their usefulness. We however also found that the membrane disturbing effect was significantly reduced when a large hydrophilic cargo was attached, which indicates that the properties of the whole peptide-cargo complex has to be taken into account (paper IV).The highly charged cell-penetrating peptide penetratin is not nearly as membrane disturbing as transportan (papers III and IV). Penetratin binds preferably to negatively charged membranes by electrostatic interactions. We used several different techniques to investigate if penetratin could be translocated through membrane model systems. All experiments consistently suggested that penetratin could not be translocated into model systems. It indicates an endocytotic uptake mechanism into cells rather than a direct membrane penetration (paper III). The ribonucleotide reductase inhibitor protein Sml1 was characterized using NMR and CD spectroscopy (paper V). Three different secondary structure elements were found, in agreement with previous NMR studies, but Sml1 does not have a well defined three-dimensional structure in solution. The N-terminus includes an α-helical region between residues 4-14 and we propose that this region interacts with the C-terminal part of the protein in the monomeric form. The N-terminus is also suggested to be a dimerization interface. Dimers are formed at concentrations above 10 µM in solution. The C-terminal region of Sml1 includes an α-helix between residues 61-80 that is crucial for binding and inhibition of RNR.
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