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Interaction between amyloid beta peptide and an aggregation blocker peptide mimicking islet amyloid polypeptide.

Rezaei-Ghaleh N, Andreetto E, Yan LM, Kapurniotu A, Zweckstetter M - PLoS ONE (2011)

Bottom Line: The most pronounced NMR chemical shift changes were observed for residues 13-20, while residues 7-9, 15-16 as well as the C-terminal half of Aβ--that is both regions of the Aβ sequence that are converted into β-strands in amyloid fibrils--were less accessible to solvent in the presence of IAPP-GI.At the same time, interaction of IAPP-GI with Aβ resulted in a concentration-dependent co-aggregation of Aβ and IAPP-GI that was enhanced for the more aggregation prone Aβ42 peptide.On the basis of the reduced toxicity of the Aβ peptide in the presence of IAPP-GI, our data are consistent with the suggestion that IAPP-GI redirects Aβ into nontoxic "off-pathway" aggregates.

View Article: PubMed Central - PubMed

Affiliation: Department for NMR-based Structural Biology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany.

ABSTRACT
Assembly of amyloid-beta peptide (Aβ) into cytotoxic oligomeric and fibrillar aggregates is believed to be a major pathologic event in Alzheimer's disease (AD) and interfering with Aβ aggregation is an important strategy in the development of novel therapeutic approaches. Prior studies have shown that the double N-methylated analogue of islet amyloid polypeptide (IAPP) IAPP-GI, which is a conformationally constrained IAPP analogue mimicking a non-amyloidogenic IAPP conformation, is capable of blocking cytotoxic self-assembly of Aβ. Here we investigate the interaction of IAPP-GI with Aβ40 and Aβ42 using NMR spectroscopy. The most pronounced NMR chemical shift changes were observed for residues 13-20, while residues 7-9, 15-16 as well as the C-terminal half of Aβ--that is both regions of the Aβ sequence that are converted into β-strands in amyloid fibrils--were less accessible to solvent in the presence of IAPP-GI. At the same time, interaction of IAPP-GI with Aβ resulted in a concentration-dependent co-aggregation of Aβ and IAPP-GI that was enhanced for the more aggregation prone Aβ42 peptide. On the basis of the reduced toxicity of the Aβ peptide in the presence of IAPP-GI, our data are consistent with the suggestion that IAPP-GI redirects Aβ into nontoxic "off-pathway" aggregates.

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Probing the water-amide proton exchange rates through a CLEANEX-PM-FHSQC experiment.A. 1H-15N-FHSQC spectrum of free Aβ40. The peak intensities of the 1H-15N-FHSQC spectrum were used as reference to calculate the relative intensity of peaks due to chemical exchange. B. CLEANEX-PM-FHSQC spectrum, measured after a selective excitation of water protons and a following 100 ms mixing time during which chemical exchange between water and amide protons occurred variably for different residues of Aβ40.
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pone-0020289-g007: Probing the water-amide proton exchange rates through a CLEANEX-PM-FHSQC experiment.A. 1H-15N-FHSQC spectrum of free Aβ40. The peak intensities of the 1H-15N-FHSQC spectrum were used as reference to calculate the relative intensity of peaks due to chemical exchange. B. CLEANEX-PM-FHSQC spectrum, measured after a selective excitation of water protons and a following 100 ms mixing time during which chemical exchange between water and amide protons occurred variably for different residues of Aβ40.

Mentions: Next, we measured sequence specific water-amide proton exchange rates for Aβ40 in the absence and presence of IAPP-GI using CLEANEX-PM-FHSQC experiments [32]. The water-amide proton exchange rate is a valuable probe of the degree of exposure of the protein backbone to the solvent: a N-H group that is buried inside the protein or involved in a hydrogen bond, will be protected from exchange with solvent. In a CLEANEX-PM-FHSQC experiment, exposed parts of the backbone gain high signal intensity already at short mixing times due to efficient exchange with water, while for more protected groups the signal intensity only rises at longer mixing times. In the absence of IAPP-GI, Gly25, Ser26, Asn27, Lys28 and Gly29 of Aβ40 showed a strong increase in NMR signal intensity already at a mixing time of 100 ms (Figure 7). The solvent exposure of these residues was further corroborated by analysis of the initial exchange rate (Figure 8A): the highest exchange rates were observed for residues Ser8-Gly9, His14, Lys16, Asp23, Gly25–Gly29 and Gly37–Gly38. Interestingly, Gln15-Val24 and Ala30-Val36 have a high tendency to adopt α-helical [33] or β-strand [34] secondary structures, while the intervening region of Val24-Gly29 tends to form a loop [35]. Additionally, solid-state NMR studies of Aβ fibrils have verified that the region between residues 23 and 29 forms an exposed turn-like structure between two β-strands [36], [37]. Altogether, the observed profile of exchange rates suggests that the monomeric free form of Aβ40 transiently samples conformational states, in which residues 10–13, 17–22 and 30–36 are partially protected from exchange with solvent. Addition of IAPP-GI results in a decrease of the exchange rate of residues Asp7, Gly9, Gln15 and Lys16, as well as Val24–Val36 (Figure 8B). The reduced exchange rates suggest that these residues are less exposed to the solvent after IAPP-GI addition. Increased protection could be a result of an intermolecular interaction between IAPP-GI and Aβ40, or alternatively caused by an IAPP-GI induced change in the conformation or assembly state of Aβ40. Support for the influence of intermolecular interactions comes from a comparison of exchange rates in Aβ40 and Aβ42. In Aβ42, which has a higher tendency for self-association, the exchange rates are reduced in regions (Figure 9) that are also affected upon addition of IAPP-GI to Aβ40 (Figure 8B).


Interaction between amyloid beta peptide and an aggregation blocker peptide mimicking islet amyloid polypeptide.

Rezaei-Ghaleh N, Andreetto E, Yan LM, Kapurniotu A, Zweckstetter M - PLoS ONE (2011)

Probing the water-amide proton exchange rates through a CLEANEX-PM-FHSQC experiment.A. 1H-15N-FHSQC spectrum of free Aβ40. The peak intensities of the 1H-15N-FHSQC spectrum were used as reference to calculate the relative intensity of peaks due to chemical exchange. B. CLEANEX-PM-FHSQC spectrum, measured after a selective excitation of water protons and a following 100 ms mixing time during which chemical exchange between water and amide protons occurred variably for different residues of Aβ40.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3102090&req=5

pone-0020289-g007: Probing the water-amide proton exchange rates through a CLEANEX-PM-FHSQC experiment.A. 1H-15N-FHSQC spectrum of free Aβ40. The peak intensities of the 1H-15N-FHSQC spectrum were used as reference to calculate the relative intensity of peaks due to chemical exchange. B. CLEANEX-PM-FHSQC spectrum, measured after a selective excitation of water protons and a following 100 ms mixing time during which chemical exchange between water and amide protons occurred variably for different residues of Aβ40.
Mentions: Next, we measured sequence specific water-amide proton exchange rates for Aβ40 in the absence and presence of IAPP-GI using CLEANEX-PM-FHSQC experiments [32]. The water-amide proton exchange rate is a valuable probe of the degree of exposure of the protein backbone to the solvent: a N-H group that is buried inside the protein or involved in a hydrogen bond, will be protected from exchange with solvent. In a CLEANEX-PM-FHSQC experiment, exposed parts of the backbone gain high signal intensity already at short mixing times due to efficient exchange with water, while for more protected groups the signal intensity only rises at longer mixing times. In the absence of IAPP-GI, Gly25, Ser26, Asn27, Lys28 and Gly29 of Aβ40 showed a strong increase in NMR signal intensity already at a mixing time of 100 ms (Figure 7). The solvent exposure of these residues was further corroborated by analysis of the initial exchange rate (Figure 8A): the highest exchange rates were observed for residues Ser8-Gly9, His14, Lys16, Asp23, Gly25–Gly29 and Gly37–Gly38. Interestingly, Gln15-Val24 and Ala30-Val36 have a high tendency to adopt α-helical [33] or β-strand [34] secondary structures, while the intervening region of Val24-Gly29 tends to form a loop [35]. Additionally, solid-state NMR studies of Aβ fibrils have verified that the region between residues 23 and 29 forms an exposed turn-like structure between two β-strands [36], [37]. Altogether, the observed profile of exchange rates suggests that the monomeric free form of Aβ40 transiently samples conformational states, in which residues 10–13, 17–22 and 30–36 are partially protected from exchange with solvent. Addition of IAPP-GI results in a decrease of the exchange rate of residues Asp7, Gly9, Gln15 and Lys16, as well as Val24–Val36 (Figure 8B). The reduced exchange rates suggest that these residues are less exposed to the solvent after IAPP-GI addition. Increased protection could be a result of an intermolecular interaction between IAPP-GI and Aβ40, or alternatively caused by an IAPP-GI induced change in the conformation or assembly state of Aβ40. Support for the influence of intermolecular interactions comes from a comparison of exchange rates in Aβ40 and Aβ42. In Aβ42, which has a higher tendency for self-association, the exchange rates are reduced in regions (Figure 9) that are also affected upon addition of IAPP-GI to Aβ40 (Figure 8B).

Bottom Line: The most pronounced NMR chemical shift changes were observed for residues 13-20, while residues 7-9, 15-16 as well as the C-terminal half of Aβ--that is both regions of the Aβ sequence that are converted into β-strands in amyloid fibrils--were less accessible to solvent in the presence of IAPP-GI.At the same time, interaction of IAPP-GI with Aβ resulted in a concentration-dependent co-aggregation of Aβ and IAPP-GI that was enhanced for the more aggregation prone Aβ42 peptide.On the basis of the reduced toxicity of the Aβ peptide in the presence of IAPP-GI, our data are consistent with the suggestion that IAPP-GI redirects Aβ into nontoxic "off-pathway" aggregates.

View Article: PubMed Central - PubMed

Affiliation: Department for NMR-based Structural Biology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany.

ABSTRACT
Assembly of amyloid-beta peptide (Aβ) into cytotoxic oligomeric and fibrillar aggregates is believed to be a major pathologic event in Alzheimer's disease (AD) and interfering with Aβ aggregation is an important strategy in the development of novel therapeutic approaches. Prior studies have shown that the double N-methylated analogue of islet amyloid polypeptide (IAPP) IAPP-GI, which is a conformationally constrained IAPP analogue mimicking a non-amyloidogenic IAPP conformation, is capable of blocking cytotoxic self-assembly of Aβ. Here we investigate the interaction of IAPP-GI with Aβ40 and Aβ42 using NMR spectroscopy. The most pronounced NMR chemical shift changes were observed for residues 13-20, while residues 7-9, 15-16 as well as the C-terminal half of Aβ--that is both regions of the Aβ sequence that are converted into β-strands in amyloid fibrils--were less accessible to solvent in the presence of IAPP-GI. At the same time, interaction of IAPP-GI with Aβ resulted in a concentration-dependent co-aggregation of Aβ and IAPP-GI that was enhanced for the more aggregation prone Aβ42 peptide. On the basis of the reduced toxicity of the Aβ peptide in the presence of IAPP-GI, our data are consistent with the suggestion that IAPP-GI redirects Aβ into nontoxic "off-pathway" aggregates.

Show MeSH
Related in: MedlinePlus