The Experts below are selected from a list of 15276 Experts worldwide ranked by ideXlab platform
Ronald Wetzel - One of the best experts on this subject based on the ideXlab platform.
-
kinetics and thermodynamics of Amyloid Fibril assembly
Accounts of Chemical Research, 2006Co-Authors: Ronald WetzelAbstract:With some exceptions, Amyloids appear to be accidental aggregated structures whose formation was not selected for in molecular evolution. Despite this, Amyloid Fibrils are in many respects surprisingly well-behaved molecules. For example, Huntington's disease-related polyglutamine sequences aggregate via a relatively simple nucleated growth polymerization mechanism. In addition, the Alzheimer's plaque protein Aβ has been shown to undergo reversible Amyloid Fibril formation to a position of dynamic equilibrium such that reaction thermodynamics can be quantified. Studies of these well-behaved Amyloid systems are allowing us to peer more deeply into the process and products of off-pathway misfolding and aggregation.
-
hydrogen deuterium h d exchange mapping of aβ1 40 Amyloid Fibril secondary structure using nuclear magnetic resonance spectroscopy
Biochemistry, 2005Co-Authors: Neil A Whittemore, Ronald Wetzel, Angela Williams, Indu Kheterpal, Rajesh Mishra, Engin H SerpersuAbstract:We describe here details of the hydrogen-deuterium (H/D) exchange behavior of the Alzheimer's peptide Aβ 1 - 4 0 , while it is a resident in the Amyloid Fibril, as determined by high-resolution solution NMR. Kinetics of H/D exchange in Aβ 1 - 4 0 Fibrils show that about half the backbone amide protons exchange during the first 25 h, while the other half remain unexchanged because of solvent inaccessibility and/or hydrogen-bonded structure. After such a treatment for 25 h with D 2 O, Fibrils of 1 5 N-enriched Aβ were dissolved in a mixture of 95% dimethyl sulfoxide (DMSO) and 5% dichloroacetic acid (DCA) and successive heteronuclear 1 H- 1 5 N HSQC spectra were collected to identify the backbone amides that did not exchange in the Fibril. These studies showed that the N and C termini of the peptide are accessible to the solvent in the Fibril state and the backbone amides of these residues are readily exchanged with bulk deuterium. In contrast, the residues in the middle of the peptide (residues 16-36) are mostly protected, suggesting that that many of the residues in this segment of the peptide are involved in a β structure in the Fibril. Two residues, G25 and S26, exhibit readily exchangeable backbone amide protons and therefore may be located on a turn or a flexible part of the peptide. Overall, the data substantially supports current models for how the Aβ peptide folds when it engages in the Amyloid Fibril structure, while also addressing some discrepancies between models.
-
hydrogen deuterium h d exchange mapping of aβ1 40 Amyloid Fibril secondary structure using nuclear magnetic resonance spectroscopy
Biochemistry, 2005Co-Authors: Neil A Whittemore, Ronald Wetzel, Angela Williams, Indu Kheterpal, Rajesh Mishra, Engin H SerpersuAbstract:We describe here details of the hydrogen−deuterium (H/D) exchange behavior of the Alzheimer's peptide Aβ1-40, while it is a resident in the Amyloid Fibril, as determined by high-resolution solution...
-
mapping aβ Amyloid Fibril secondary structure using scanning proline mutagenesis
Journal of Molecular Biology, 2004Co-Authors: Angela Williams, Erik Portelius, Indu Kheterpal, Juntao Guo, Kelsey D Cook, Ronald WetzelAbstract:Although the Amyloid Fibrils formed from the Alzheimer's disease Amyloid peptide Abeta are rich in cross-beta sheet, the peptide likely also exhibits turn and unstructured regions when it becomes incorporated into Amyloid. We generated a series of single-proline replacement mutants of Abeta(1-40) and determined the thermodynamic stabilities of Amyloid Fibrils formed from these mutants to characterize the susceptibility of different residue positions of the Abeta sequence to proline substitution. The results suggest that the Abeta peptide, when engaged in the Amyloid Fibril, folds into a conformation containing three highly structured segments, consisting of contiguous sequence elements 15-21, 24-28, and 31-36, that are sensitive to proline replacement and likely to include the beta-sheet portions of the Fibrils. Residues relatively insensitive to proline replacement fall into two groups: (a) residues 1-14 and 37-40 are likely to exist in relatively unstructured, flexible elements extruded from the beta-sheet-rich Amyloid core; (b) residues 22, 23, 29 and 30 are likely to occupy turn positions between these three structured elements. Although destabilized, Fibrils formed from Abeta(1-40) proline mutants are very similar in structure to wild-type Fibrils, as indicated by hydrogen-deuterium exchange and other analysis. Interestingly, however, some proline mutations destabilize Fibrils while at the same time increasing the number of amide protons protected from hydrogen exchange. This suggests that the stability of Amyloid Fibrils, rather than being driven exclusively by the formation of H-bonded beta-sheet, is achieved, as in globular proteins, through a balance of stabilizing and destabilizing forces. The proline scanning data are most compatible with a model for Amyloid protofilament structure loosely resembling the parallel beta-helix folding motif, such that each Abeta(15-36) core region occupies a single layer of a prismatic, H-bonded stack of peptides.
-
mapping aβ Amyloid Fibril secondary structure using scanning proline mutagenesis
Journal of Molecular Biology, 2004Co-Authors: Angela Williams, Erik Portelius, Indu Kheterpal, Kelsey D Cook, Ying Xu, Ronald WetzelAbstract:Abstract Although the Amyloid Fibrils formed from the Alzheimer's disease Amyloid peptide Aβ are rich in cross-β sheet, the peptide likely also exhibits turn and unstructured regions when it becomes incorporated into Amyloid. We generated a series of single-proline replacement mutants of Aβ(1–40) and determined the thermodynamic stabilities of Amyloid Fibrils formed from these mutants to characterize the susceptibility of different residue positions of the Aβ sequence to proline substitution. The results suggest that the Aβ peptide, when engaged in the Amyloid Fibril, folds into a conformation containing three highly structured segments, consisting of contiguous sequence elements 15–21, 24–28, and 31–36, that are sensitive to proline replacement and likely to include the β-sheet portions of the Fibrils. Residues relatively insensitive to proline replacement fall into two groups: (a) residues 1–14 and 37–40 are likely to exist in relatively unstructured, flexible elements extruded from the β-sheet-rich Amyloid core; (b) residues 22, 23, 29 and 30 are likely to occupy turn positions between these three structured elements. Although destabilized, Fibrils formed from Aβ(1–40) proline mutants are very similar in structure to wild-type Fibrils, as indicated by hydrogen–deuterium exchange and other analysis. Interestingly, however, some proline mutations destabilize Fibrils while at the same time increasing the number of amide protons protected from hydrogen exchange. This suggests that the stability of Amyloid Fibrils, rather than being driven exclusively by the formation of H-bonded β-sheet, is achieved, as in globular proteins, through a balance of stabilizing and destabilizing forces. The proline scanning data are most compatible with a model for Amyloid protofilament structure loosely resembling the parallel β-helix folding motif, such that each Aβ(15–36) core region occupies a single layer of a prismatic, H-bonded stack of peptides.
Jeffery W Kelly - One of the best experts on this subject based on the ideXlab platform.
-
evaluating the binding selectivity of transthyretin Amyloid Fibril inhibitors in blood plasma
Proceedings of the National Academy of Sciences of the United States of America, 2001Co-Authors: Hans E Purkey, Michael I Dorrell, Jeffery W KellyAbstract:Abstract Transthyretin (TTR) tetramer dissociation and misfolding facilitate assembly into Amyloid Fibrils that putatively cause senile systemic Amyloidosis and familial Amyloid polyneuropathy. We have previously discovered more than 50 small molecules that bind to and stabilize tetrameric TTR, inhibiting Amyloid Fibril formation in vitro. A method is presented here to evaluate the binding selectivity of these inhibitors to TTR in human plasma, a complex biological fluid composed of more than 60 proteins and numerous small molecules. Our immunoprecipitation approach isolates TTR and bound small molecules from a biological fluid such as plasma, and quantifies the amount of small molecules bound to the protein by HPLC analysis. This approach demonstrates that only a small subset of the inhibitors that saturate the TTR binding sites in vitro do so in plasma. These selective inhibitors can now be tested in animal models of TTR Amyloid disease to probe the validity of the Amyloid hypothesis. This method could be easily extended to evaluate small molecule binding selectivity to any protein in a given biological fluid without the necessity of determining or guessing which other protein components may be competitors. This is a central issue to understanding the distribution, metabolism, activity, and toxicity of potential drugs.
-
protofilaments filaments ribbons and Fibrils from peptidomimetic self assembly implications for Amyloid Fibril formation and materials science
Journal of the American Chemical Society, 2000Co-Authors: Hilal A Lashuel, Louise C Serpell, Steven R Labrenz, Linda Woo, Jeffery W KellyAbstract:Deciphering the mechanism(s) of beta-sheet mediated self-assembly is essential for understanding Amyloid Fibril formation and for the fabrication of polypeptide materials. Herein, we report a simple peptidomimetic that self-assembles into polymorphic beta-sheet quaternary structures including protofilaments, filaments, Fibrils, and ribbons that are reminiscent of the highly ordered structures displayed by the Amyloidogenic peptides A beta, calcitonin, and amylin. The distribution of quaternary structures can be controlled by and in some cases specified by manipulating the pH, buffer composition, and the ionic strength. The ability to control beta-sheet-mediated assembly takes advantage of quaternary structure dependent pK(a) perturbations. Biophysical methods including analytical ultracentrifugation studies as well as far-UV circular dichroism and FT-IR spectroscopy demonstrate that linked secondary and quaternary structural changes mediate peptidomimetic self-assembly. Electron and atomic force microscopy reveal that peptidomimetic assembly involves numerous quaternary structural intermediates that appear to self-assemble in a convergent fashion affording quaternary structures of increasing complexity. The ability to control the assembly pathway(s) and the final quaternary structure(s) afforded should prove to be particularly useful in deciphering the quaternary structural requirements for Amyloid Fibril formation and for the construction of noncovalent macromolecular structures
-
protofilaments filaments ribbons and Fibrils from peptidomimetic self assembly implications for Amyloid Fibril formation and materials science
Journal of the American Chemical Society, 2000Co-Authors: Hilal A Lashuel, Louise C Serpell, Steven R Labrenz, Jeffery W KellyAbstract:Deciphering the mechanism(s) of β-sheet mediated self-assembly is essential for understanding Amyloid Fibril formation and for the fabrication of polypeptide materials. Herein, we report a simple peptidomimetic that self-assembles into polymorphic β-sheet quaternary structures including protofilaments, filaments, Fibrils, and ribbons that are reminiscent of the highly ordered structures displayed by the Amyloidogenic peptides Aβ, calcitonin, and amylin. The distribution of quaternary structures can be controlled by and in some cases specified by manipulating the pH, buffer composition, and the ionic strength. The ability to control β-sheet-mediated assembly takes advantage of quaternary structure dependent pKa perturbations. Biophysical methods including analytical ultracentrifugation studies as well as far-UV circular dichroism and FT-IR spectroscopy demonstrate that linked secondary and quaternary structural changes mediate peptidomimetic self-assembly. Electron and atomic force microscopy reveal that p...
-
structure based design of n phenyl phenoxazine transthyretin Amyloid Fibril inhibitors
Journal of the American Chemical Society, 2000Co-Authors: Michael H Petrassi, And James Sacchettini, Thomas Klabunde, Jeffery W KellyAbstract:Starting with the published 2.0 A X-ray crystal structure of the transthyretin·(flufenamic acid)2 complex, a simple structure-based ligand design strategy was employed to conceive of N-phenyl phenoxazine transthyretin (TTR) Amyloid Fibril inhibitors. Fifteen N-phenyl phenoxazines were chemically synthesized and evaluated using a quantitative Amyloid Fibril assay in vitro. The structure of one of the two most active phenoxazines, 4, bound to TTR was solved to a resolution of 1.9 A to understand the structural basis of its efficacy. N-phenyl phenoxazine 4 binds similar to the orientation anticipated, although not as deeply into the channel as expected. Like flufenamic acid, 4 mediates binding-induced conformational changes that enable intersubunit H-bonding in tetrameric TTR which may be important for preventing Fibril formation. Analytical ultracentrifugation analysis demonstrates that 4 blocks the first step of TTR Amyloid Fibril formation, that is, tetramer dissociation to the alternatively folded amyloi...
-
synthesis and evaluation of anthranilic acid based transthyretin Amyloid Fibril inhibitors
Bioorganic & Medicinal Chemistry Letters, 1999Co-Authors: Vibha Oza, Michael H Petrassi, Hans E Purkey, Jeffery W KellyAbstract:Eight small molecules were synthesized to evaluate the structure activity relationships (SAR) of N-substituted anthranilic acids. The molecules were synthesized by benzylation or arylation of methyl anthranilate. A light scattering-based Amyloid Fibril formation assay was used to evaluate potential inhibitors of transthyretin (TTR) Amyloid Fibril formation in vitro. The m-carboxyphenylated and o-trifluoromethylphenylated anthranilic acids are potent inhibitors that will be subjected to further SAR and structural analysis.
Angela Williams - One of the best experts on this subject based on the ideXlab platform.
-
hydrogen deuterium h d exchange mapping of aβ1 40 Amyloid Fibril secondary structure using nuclear magnetic resonance spectroscopy
Biochemistry, 2005Co-Authors: Neil A Whittemore, Ronald Wetzel, Angela Williams, Indu Kheterpal, Rajesh Mishra, Engin H SerpersuAbstract:We describe here details of the hydrogen-deuterium (H/D) exchange behavior of the Alzheimer's peptide Aβ 1 - 4 0 , while it is a resident in the Amyloid Fibril, as determined by high-resolution solution NMR. Kinetics of H/D exchange in Aβ 1 - 4 0 Fibrils show that about half the backbone amide protons exchange during the first 25 h, while the other half remain unexchanged because of solvent inaccessibility and/or hydrogen-bonded structure. After such a treatment for 25 h with D 2 O, Fibrils of 1 5 N-enriched Aβ were dissolved in a mixture of 95% dimethyl sulfoxide (DMSO) and 5% dichloroacetic acid (DCA) and successive heteronuclear 1 H- 1 5 N HSQC spectra were collected to identify the backbone amides that did not exchange in the Fibril. These studies showed that the N and C termini of the peptide are accessible to the solvent in the Fibril state and the backbone amides of these residues are readily exchanged with bulk deuterium. In contrast, the residues in the middle of the peptide (residues 16-36) are mostly protected, suggesting that that many of the residues in this segment of the peptide are involved in a β structure in the Fibril. Two residues, G25 and S26, exhibit readily exchangeable backbone amide protons and therefore may be located on a turn or a flexible part of the peptide. Overall, the data substantially supports current models for how the Aβ peptide folds when it engages in the Amyloid Fibril structure, while also addressing some discrepancies between models.
-
hydrogen deuterium h d exchange mapping of aβ1 40 Amyloid Fibril secondary structure using nuclear magnetic resonance spectroscopy
Biochemistry, 2005Co-Authors: Neil A Whittemore, Ronald Wetzel, Angela Williams, Indu Kheterpal, Rajesh Mishra, Engin H SerpersuAbstract:We describe here details of the hydrogen−deuterium (H/D) exchange behavior of the Alzheimer's peptide Aβ1-40, while it is a resident in the Amyloid Fibril, as determined by high-resolution solution...
-
mapping aβ Amyloid Fibril secondary structure using scanning proline mutagenesis
Journal of Molecular Biology, 2004Co-Authors: Angela Williams, Erik Portelius, Indu Kheterpal, Juntao Guo, Kelsey D Cook, Ronald WetzelAbstract:Although the Amyloid Fibrils formed from the Alzheimer's disease Amyloid peptide Abeta are rich in cross-beta sheet, the peptide likely also exhibits turn and unstructured regions when it becomes incorporated into Amyloid. We generated a series of single-proline replacement mutants of Abeta(1-40) and determined the thermodynamic stabilities of Amyloid Fibrils formed from these mutants to characterize the susceptibility of different residue positions of the Abeta sequence to proline substitution. The results suggest that the Abeta peptide, when engaged in the Amyloid Fibril, folds into a conformation containing three highly structured segments, consisting of contiguous sequence elements 15-21, 24-28, and 31-36, that are sensitive to proline replacement and likely to include the beta-sheet portions of the Fibrils. Residues relatively insensitive to proline replacement fall into two groups: (a) residues 1-14 and 37-40 are likely to exist in relatively unstructured, flexible elements extruded from the beta-sheet-rich Amyloid core; (b) residues 22, 23, 29 and 30 are likely to occupy turn positions between these three structured elements. Although destabilized, Fibrils formed from Abeta(1-40) proline mutants are very similar in structure to wild-type Fibrils, as indicated by hydrogen-deuterium exchange and other analysis. Interestingly, however, some proline mutations destabilize Fibrils while at the same time increasing the number of amide protons protected from hydrogen exchange. This suggests that the stability of Amyloid Fibrils, rather than being driven exclusively by the formation of H-bonded beta-sheet, is achieved, as in globular proteins, through a balance of stabilizing and destabilizing forces. The proline scanning data are most compatible with a model for Amyloid protofilament structure loosely resembling the parallel beta-helix folding motif, such that each Abeta(15-36) core region occupies a single layer of a prismatic, H-bonded stack of peptides.
-
mapping aβ Amyloid Fibril secondary structure using scanning proline mutagenesis
Journal of Molecular Biology, 2004Co-Authors: Angela Williams, Erik Portelius, Indu Kheterpal, Kelsey D Cook, Ying Xu, Ronald WetzelAbstract:Abstract Although the Amyloid Fibrils formed from the Alzheimer's disease Amyloid peptide Aβ are rich in cross-β sheet, the peptide likely also exhibits turn and unstructured regions when it becomes incorporated into Amyloid. We generated a series of single-proline replacement mutants of Aβ(1–40) and determined the thermodynamic stabilities of Amyloid Fibrils formed from these mutants to characterize the susceptibility of different residue positions of the Aβ sequence to proline substitution. The results suggest that the Aβ peptide, when engaged in the Amyloid Fibril, folds into a conformation containing three highly structured segments, consisting of contiguous sequence elements 15–21, 24–28, and 31–36, that are sensitive to proline replacement and likely to include the β-sheet portions of the Fibrils. Residues relatively insensitive to proline replacement fall into two groups: (a) residues 1–14 and 37–40 are likely to exist in relatively unstructured, flexible elements extruded from the β-sheet-rich Amyloid core; (b) residues 22, 23, 29 and 30 are likely to occupy turn positions between these three structured elements. Although destabilized, Fibrils formed from Aβ(1–40) proline mutants are very similar in structure to wild-type Fibrils, as indicated by hydrogen–deuterium exchange and other analysis. Interestingly, however, some proline mutations destabilize Fibrils while at the same time increasing the number of amide protons protected from hydrogen exchange. This suggests that the stability of Amyloid Fibrils, rather than being driven exclusively by the formation of H-bonded β-sheet, is achieved, as in globular proteins, through a balance of stabilizing and destabilizing forces. The proline scanning data are most compatible with a model for Amyloid protofilament structure loosely resembling the parallel β-helix folding motif, such that each Aβ(15–36) core region occupies a single layer of a prismatic, H-bonded stack of peptides.
-
structural features of the aβ Amyloid Fibril elucidated by limited proteolysis
Biochemistry, 2001Co-Authors: Indu Kheterpal, Angela Williams, Charles L Murphy, Brian Bledsoe, Ronald WetzelAbstract:Although the gross morphology of Amyloid Fibrils is fairly well understood, very little is known about how the constituent polypeptides fold within the Amyloid folding motif. In the experiments reported here, we used trypsin and chymotrypsin to conduct limited proteolysis studies on synthetic Amyloid Fibrils composed of the Alzheimer's disease peptide Aβ(1−40). In both reactions, the extreme N-terminal proteolytic fragment is released from Fibrils as rapidly as it is from the Aβ monomer, while other proteolytic fragments are generated much more slowly. Furthermore, aggregated material isolated by centrifugation of intermediate digestion time points from both proteases contains, in addition to full-length material, peptides that possess mature C-termini but truncated N-termini. These data strongly suggest that the N-terminal region of Aβ is not involved in the β-sheet network of the Amyloid Fibril, while the C-terminus is essentially completely engaged in protectivepresumably β-sheetstructure. In both dige...
Indu Kheterpal - One of the best experts on this subject based on the ideXlab platform.
-
hydrogen deuterium h d exchange mapping of aβ1 40 Amyloid Fibril secondary structure using nuclear magnetic resonance spectroscopy
Biochemistry, 2005Co-Authors: Neil A Whittemore, Ronald Wetzel, Angela Williams, Indu Kheterpal, Rajesh Mishra, Engin H SerpersuAbstract:We describe here details of the hydrogen-deuterium (H/D) exchange behavior of the Alzheimer's peptide Aβ 1 - 4 0 , while it is a resident in the Amyloid Fibril, as determined by high-resolution solution NMR. Kinetics of H/D exchange in Aβ 1 - 4 0 Fibrils show that about half the backbone amide protons exchange during the first 25 h, while the other half remain unexchanged because of solvent inaccessibility and/or hydrogen-bonded structure. After such a treatment for 25 h with D 2 O, Fibrils of 1 5 N-enriched Aβ were dissolved in a mixture of 95% dimethyl sulfoxide (DMSO) and 5% dichloroacetic acid (DCA) and successive heteronuclear 1 H- 1 5 N HSQC spectra were collected to identify the backbone amides that did not exchange in the Fibril. These studies showed that the N and C termini of the peptide are accessible to the solvent in the Fibril state and the backbone amides of these residues are readily exchanged with bulk deuterium. In contrast, the residues in the middle of the peptide (residues 16-36) are mostly protected, suggesting that that many of the residues in this segment of the peptide are involved in a β structure in the Fibril. Two residues, G25 and S26, exhibit readily exchangeable backbone amide protons and therefore may be located on a turn or a flexible part of the peptide. Overall, the data substantially supports current models for how the Aβ peptide folds when it engages in the Amyloid Fibril structure, while also addressing some discrepancies between models.
-
hydrogen deuterium h d exchange mapping of aβ1 40 Amyloid Fibril secondary structure using nuclear magnetic resonance spectroscopy
Biochemistry, 2005Co-Authors: Neil A Whittemore, Ronald Wetzel, Angela Williams, Indu Kheterpal, Rajesh Mishra, Engin H SerpersuAbstract:We describe here details of the hydrogen−deuterium (H/D) exchange behavior of the Alzheimer's peptide Aβ1-40, while it is a resident in the Amyloid Fibril, as determined by high-resolution solution...
-
mapping aβ Amyloid Fibril secondary structure using scanning proline mutagenesis
Journal of Molecular Biology, 2004Co-Authors: Angela Williams, Erik Portelius, Indu Kheterpal, Juntao Guo, Kelsey D Cook, Ronald WetzelAbstract:Although the Amyloid Fibrils formed from the Alzheimer's disease Amyloid peptide Abeta are rich in cross-beta sheet, the peptide likely also exhibits turn and unstructured regions when it becomes incorporated into Amyloid. We generated a series of single-proline replacement mutants of Abeta(1-40) and determined the thermodynamic stabilities of Amyloid Fibrils formed from these mutants to characterize the susceptibility of different residue positions of the Abeta sequence to proline substitution. The results suggest that the Abeta peptide, when engaged in the Amyloid Fibril, folds into a conformation containing three highly structured segments, consisting of contiguous sequence elements 15-21, 24-28, and 31-36, that are sensitive to proline replacement and likely to include the beta-sheet portions of the Fibrils. Residues relatively insensitive to proline replacement fall into two groups: (a) residues 1-14 and 37-40 are likely to exist in relatively unstructured, flexible elements extruded from the beta-sheet-rich Amyloid core; (b) residues 22, 23, 29 and 30 are likely to occupy turn positions between these three structured elements. Although destabilized, Fibrils formed from Abeta(1-40) proline mutants are very similar in structure to wild-type Fibrils, as indicated by hydrogen-deuterium exchange and other analysis. Interestingly, however, some proline mutations destabilize Fibrils while at the same time increasing the number of amide protons protected from hydrogen exchange. This suggests that the stability of Amyloid Fibrils, rather than being driven exclusively by the formation of H-bonded beta-sheet, is achieved, as in globular proteins, through a balance of stabilizing and destabilizing forces. The proline scanning data are most compatible with a model for Amyloid protofilament structure loosely resembling the parallel beta-helix folding motif, such that each Abeta(15-36) core region occupies a single layer of a prismatic, H-bonded stack of peptides.
-
mapping aβ Amyloid Fibril secondary structure using scanning proline mutagenesis
Journal of Molecular Biology, 2004Co-Authors: Angela Williams, Erik Portelius, Indu Kheterpal, Kelsey D Cook, Ying Xu, Ronald WetzelAbstract:Abstract Although the Amyloid Fibrils formed from the Alzheimer's disease Amyloid peptide Aβ are rich in cross-β sheet, the peptide likely also exhibits turn and unstructured regions when it becomes incorporated into Amyloid. We generated a series of single-proline replacement mutants of Aβ(1–40) and determined the thermodynamic stabilities of Amyloid Fibrils formed from these mutants to characterize the susceptibility of different residue positions of the Aβ sequence to proline substitution. The results suggest that the Aβ peptide, when engaged in the Amyloid Fibril, folds into a conformation containing three highly structured segments, consisting of contiguous sequence elements 15–21, 24–28, and 31–36, that are sensitive to proline replacement and likely to include the β-sheet portions of the Fibrils. Residues relatively insensitive to proline replacement fall into two groups: (a) residues 1–14 and 37–40 are likely to exist in relatively unstructured, flexible elements extruded from the β-sheet-rich Amyloid core; (b) residues 22, 23, 29 and 30 are likely to occupy turn positions between these three structured elements. Although destabilized, Fibrils formed from Aβ(1–40) proline mutants are very similar in structure to wild-type Fibrils, as indicated by hydrogen–deuterium exchange and other analysis. Interestingly, however, some proline mutations destabilize Fibrils while at the same time increasing the number of amide protons protected from hydrogen exchange. This suggests that the stability of Amyloid Fibrils, rather than being driven exclusively by the formation of H-bonded β-sheet, is achieved, as in globular proteins, through a balance of stabilizing and destabilizing forces. The proline scanning data are most compatible with a model for Amyloid protofilament structure loosely resembling the parallel β-helix folding motif, such that each Aβ(15–36) core region occupies a single layer of a prismatic, H-bonded stack of peptides.
-
structural features of the aβ Amyloid Fibril elucidated by limited proteolysis
Biochemistry, 2001Co-Authors: Indu Kheterpal, Angela Williams, Charles L Murphy, Brian Bledsoe, Ronald WetzelAbstract:Although the gross morphology of Amyloid Fibrils is fairly well understood, very little is known about how the constituent polypeptides fold within the Amyloid folding motif. In the experiments reported here, we used trypsin and chymotrypsin to conduct limited proteolysis studies on synthetic Amyloid Fibrils composed of the Alzheimer's disease peptide Aβ(1−40). In both reactions, the extreme N-terminal proteolytic fragment is released from Fibrils as rapidly as it is from the Aβ monomer, while other proteolytic fragments are generated much more slowly. Furthermore, aggregated material isolated by centrifugation of intermediate digestion time points from both proteases contains, in addition to full-length material, peptides that possess mature C-termini but truncated N-termini. These data strongly suggest that the N-terminal region of Aβ is not involved in the β-sheet network of the Amyloid Fibril, while the C-terminus is essentially completely engaged in protectivepresumably β-sheetstructure. In both dige...
Engin H Serpersu - One of the best experts on this subject based on the ideXlab platform.
-
hydrogen deuterium h d exchange mapping of aβ1 40 Amyloid Fibril secondary structure using nuclear magnetic resonance spectroscopy
Biochemistry, 2005Co-Authors: Neil A Whittemore, Ronald Wetzel, Angela Williams, Indu Kheterpal, Rajesh Mishra, Engin H SerpersuAbstract:We describe here details of the hydrogen-deuterium (H/D) exchange behavior of the Alzheimer's peptide Aβ 1 - 4 0 , while it is a resident in the Amyloid Fibril, as determined by high-resolution solution NMR. Kinetics of H/D exchange in Aβ 1 - 4 0 Fibrils show that about half the backbone amide protons exchange during the first 25 h, while the other half remain unexchanged because of solvent inaccessibility and/or hydrogen-bonded structure. After such a treatment for 25 h with D 2 O, Fibrils of 1 5 N-enriched Aβ were dissolved in a mixture of 95% dimethyl sulfoxide (DMSO) and 5% dichloroacetic acid (DCA) and successive heteronuclear 1 H- 1 5 N HSQC spectra were collected to identify the backbone amides that did not exchange in the Fibril. These studies showed that the N and C termini of the peptide are accessible to the solvent in the Fibril state and the backbone amides of these residues are readily exchanged with bulk deuterium. In contrast, the residues in the middle of the peptide (residues 16-36) are mostly protected, suggesting that that many of the residues in this segment of the peptide are involved in a β structure in the Fibril. Two residues, G25 and S26, exhibit readily exchangeable backbone amide protons and therefore may be located on a turn or a flexible part of the peptide. Overall, the data substantially supports current models for how the Aβ peptide folds when it engages in the Amyloid Fibril structure, while also addressing some discrepancies between models.
-
hydrogen deuterium h d exchange mapping of aβ1 40 Amyloid Fibril secondary structure using nuclear magnetic resonance spectroscopy
Biochemistry, 2005Co-Authors: Neil A Whittemore, Ronald Wetzel, Angela Williams, Indu Kheterpal, Rajesh Mishra, Engin H SerpersuAbstract:We describe here details of the hydrogen−deuterium (H/D) exchange behavior of the Alzheimer's peptide Aβ1-40, while it is a resident in the Amyloid Fibril, as determined by high-resolution solution...