| 1. |
- Brorsson, Ann-Christin, et al.
(författare)
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Intrinsic determinants of neurotoxic aggregate formation by the amyloid beta peptide
- 2010
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Ingår i: Biophysical Journal. - : Elsevier BV. - 0006-3495 .- 1542-0086. ; 98:8, s. 1677-84
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Tidskriftsartikel (refereegranskat)abstract
- The extent to which proteins aggregate into distinct structures ranging from prefibrillar oligomers to amyloid fibrils is key to the pathogenesis of many age-related degenerative diseases. We describe here for the Alzheimer's disease-related amyloid beta peptide (Abeta) an investigation of the sequence-based determinants of the balance between the formation of prefibrillar aggregates and amyloid fibrils. We show that by introducing single-point mutations, it is possible to convert the normally harmless Abeta40 peptide into a pathogenic species by increasing its relative propensity to form prefibrillar but not fibrillar aggregates, and, conversely, to abolish the pathogenicity of the highly neurotoxic E22G Abeta42 peptide by reducing its relative propensity to form prefibrillar species rather than mature fibrillar ones. This observation can be rationalized by the demonstration that whereas regions of the sequence of high aggregation propensity dominate the overall tendency to aggregate, regions with low intrinsic aggregation propensities exert significant control over the balance of the prefibrillar and fibrillar species formed, and therefore play a major role in determining the neurotoxicity of the Abeta peptide.
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| 2. |
- Favrin, Giorgio, et al.
(författare)
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Folding of a small helical protein using hydrogen bonds and hydrophobicity forces.
- 2002
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Ingår i: Proteins. - : Wiley. - 0887-3585. ; 47:2, s. 99-105
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Tidskriftsartikel (refereegranskat)abstract
- A reduced protein model with five to six atoms per amino acid and five amino acid types is developed and tested on a three-helix-bundle protein, a 46-amino acid fragment from staphylococcal protein A. The model does not rely on the widely used Go approximation, which ignores non-native interactions. We find that the collapse transition is considerably more abrupt for the protein A sequence than for random sequences with the same composition. The chain collapse is found to be at least as fast as helix formation. Energy minimization restricted to the thermodynamically favored topology gives a structure that has a root-mean-square deviation of 1.8 A from the native structure. The sequence-dependent part of our potential is pairwise additive. Our calculations suggest that fine-tuning this potential by parameter optimization is of limited use.
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| 3. |
- Favrin, Giorgio, et al.
(författare)
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Monte Carlo update for chain molecules: Biased Gaussian steps in torsional space
- 2001
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 114:8, s. 8154-8158
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Tidskriftsartikel (refereegranskat)abstract
- We develop a new elementary move for simulations of polymer chains in torsion angle space. The method is flexible and easy to implement. Tentative updates are drawn from a (conformation-dependent) Gaussian distribution that favors approximately local deformations of the chain. The degree of bias is controlled by a parameter b. The method is tested on a reduced model protein with 54 amino acids and the Ramachandran torsion angles as its only degrees of freedom, for different b. Without excessive fine tuning, we find that the effective step size can be increased by a factor of 3 compared to the unbiased b = 0 case. The method may be useful for kinetic studies, too.
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| 4. |
- Favrin, Giorgio, et al.
(författare)
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Oligomerization of amyloid A beta(16-22) peptides using hydrogen bonds and hydrophobicity forces
- 2004
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Ingår i: Biophysical Journal. - : Elsevier BV. - 1542-0086 .- 0006-3495. ; 87:6, s. 3657-3664
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Tidskriftsartikel (refereegranskat)abstract
- The 16 - 22 amino-acid fragment of the beta-amyloid peptide associated with the Alzheimer's disease, Abeta, is capable of forming amyloid fibrils. Here we study the aggregation mechanism of Abeta(16-22) peptides by unbiased thermodynamic simulations at the atomic level for systems of one, three, and six Abeta(16-22) peptides. We find that the isolated Abeta(16-22) peptide is mainly a random coil in the sense that both the alpha-helix and beta-strand contents are low, whereas the three- and six-chain systems form aggregated structures with a high beta-sheet content. Furthermore, in agreement with experiments on Abeta(16-22) fibrils, we find that large parallel beta-sheets are unlikely to form. For the six-chain system, the aggregated structures can have many different shapes, but certain particularly stable shapes can be identified.
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| 5. |
- Favrin, Giorgio, et al.
(författare)
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Sequence-based study of two related proteins with different folding behaviors
- 2004
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Ingår i: Proteins. - : Wiley. - 0887-3585. ; 54:1, s. 8-12
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Tidskriftsartikel (refereegranskat)abstract
- Z(SPA-1) is an engineered protein that binds to its parent, the three-helix-bundle Z domain of staphylococcal protein A. Uncomplexed Z(SPA-1) shows a reduced helix content and a melting behavior that is less cooperative, compared with the wild-type Z domain. Here we show that the difference in folding behavior between these two sequences can be partly understood in terms of an off-lattice model with 5-6 atoms per amino acid and a minimalistic potential, in which folding is driven by backbone hydrogen bonding and effective hydrophobic attraction. (C) 2003 Wiley-Liss, Inc.
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| 6. |
- Favrin, Giorgio
(författare)
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Statistical Physics of Protein Folding and Aggregation
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The mechanisms of protein folding and aggregation are investigated by computer simulations of all-atom and reduced models with sequence-based potentials. A quasi local Monte Carlo update is developed in order to efficiently sample proteins in the folded phase. A small helical protein, the B-domain of staphylococcal protein A, is studied using a reduced model. In the thermodynamically favoured topology, energy minimisation leads to a conformation whose root mean square deviation form the experimental structure is 1.8Å. We also study the thermodynamics and kinetics of small fast folding proteins without a clear free-energy barrier between the folded and unfolded states. Analytical calculations using a square well-potential enable us to predict the relaxation time within a factor of two. Finally using an all atom model, we study the aggregation properties of a 7-amino acid fragment of Alzheimer's amyloid beta peptide. We find that the system of three and six such fragments form aggregated structures with a high content of antiparallel beta-sheet structure, which is in line with experimental data.
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| 7. |
- Favrin, Giorgio, et al.
(författare)
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Two-state folding over a weak free-energy barrier
- 2003
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Ingår i: Biophysical Journal. - 1542-0086. ; 85:3, s. 1457-1465
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Tidskriftsartikel (refereegranskat)abstract
- We present a Monte Carlo study of a model protein with 54 amino acids that folds directly to its native three-helix-bundle state without forming any well-defined intermediate state. The free-energy barrier separating the native and unfolded states of this protein is found to be weak, even at the folding temperature. Nevertheless, we find that melting curves to a good approximation can be described in terms of a simple two-state system, and that the relaxation behavior is close to single exponential. The motion along individual reaction coordinates is roughly diffusive on timescales beyond the reconfiguration time for a single helix. A simple estimate based on diffusion in a square-well potential predicts the relaxation time within a factor of two.
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| 8. |
- Mohanty, Sandipan, et al.
(författare)
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Protein folding, aggregation and unfolding in Monte Carlo Simulations
- 2010
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Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3892. ; 7, s. 68-71
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Konferensbidrag (refereegranskat)abstract
- An implicit water all-atom model is used to study folding, aggregation and mechanical unfolding of small proteins. Physically reasonable results obtained for a variety of applications indicate healthy global properties of the interaction potential.
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