Alternate aggregation pathways of the Alzheimer beta-amyloid peptide: Abeta association kinetics at endosomal pH

The deposition of beta-amyloid peptide (Abeta) fibrils around neurons is an invariable feature of Alzheimer's disease and there is increasing evidence that fibrillar deposits and/or prefibrillar intermediates play a central role in the observed neurodegeneration. One site of Abeta generation is the endosomes, and we have investigated the kinetics of Abeta association at endosomal pH over physiologically relevant time frames. We have identified three distinct Abeta association phases that occur at rates comparable to endosomal transit times. Rapid formation of burst phase aggregates, larger than 200nm, was observed within 15 seconds. Two slower association phases were detected by fluorescence resonance energy transfer and termed phase 1 and phase 2 aggregation reactions. At 20 microM Abeta, pH 6, the half lives of the phase 1 and phase 2 aggregation phases were 3.15 minutes and 17.66 minutes, respectively. Atomic force microscopy and dynamic light scattering studies indicate that the burst phase aggregate is large and amorphous, while phase 1 and 2 aggregates are spherical with hydrodynamic radii around 30 nm. There is an apparent equilibrium, potentially mediated through a soluble Abeta intermediate, between the large burst phase aggregates and phase 1 and 2 spherical particles. The large burst phase aggregates form quickly, however, they disappear as the equilibrium shifts toward the spherical aggregates. These aggregated species do not contain alpha-helical or beta-structure as determined by circular dichroism spectroscopy. However, after two weeks beta-structure is observed and is attributable to the insoluble portion of the sample. After two months, mature amyloid fibrils appear and the spherical aggregates are significantly diminished.     

Time-resolved infrared spectroscopy of pH-induced aggregation of the Alzheimer Abeta(1-28) peptide

Aggregation of the Alzheimer's disease-related Aβ_1-28 peptide was induced by a rapid, sub-millisecond pH jump and monitored by time-resolved infrared spectroscopy on the millisecond to second time-scale. The release of protons was induced by the photolysis of a caged compound, 1-(2-nitrophenyl)ethyl sulfate (NPE-sulfate). The pH jump generated in our experimental setup is used to model the Aβ peptide structural conversions that may occur in the acidic endosomal/lysosomal cell compartment system. The aggregation of the Aβ_1-28 peptide induced by the pH jump from 8.5 to < 6 yields an antiparallel β-sheet structure. The kinetics of the structural transition is biphasic, showing an initial rapid phase with a transition from random coil to an oligomeric β-sheet form with a time constant of 3.6 s. This phase is followed by a second slower transition, which yields larger aggregates during 48.0 s.     

Amyloid beta-protein (Abeta)1-40 protects neurons from damage induced by Abeta1-42 in culture and in rat brain

Previously, we found that amyloid beta-protein (Abeta)1-42 exhibits neurotoxicity, while Abeta1-40 serves as an antioxidant molecule by quenching metal ions and inhibiting metal-mediated oxygen radical generation. Here, we show another neuroprotective action of nonamyloidogenic Abeta1-40 against Abeta1-42-induced neurotoxicity in culture and in vivo. Neuronal death was induced by Abeta1-42 at concentrations higher than 2 microm, which was prevented by concurrent treatment with Abeta1-40 in a dose-dependent manner. However, metal chelators did not prevent Abeta1-42-induced neuronal death. Circular dichroism spectroscopy showed that Abeta1-40 inhibited the beta-sheet transformation of Abeta1-42. Thioflavin-T assay and electron microscopy analysis revealed that Abeta1-40 inhibited the fibril formation of Abeta1-42. In contrast, Abeta1-16, Abeta25-35, and Abeta40-1 did not inhibit the fibril formation of Abeta1-42 nor prevent Abeta1-42-induced neuronal death. Abeta1-42 injection into the rat entorhinal cortex (EC) caused the hyperphosphorylation of tau on both sides of EC and hippocampus and increased the number of glial fibrillary acidic protein (GFAP)-positive astrocytes in the ipsilateral EC, which were prevented by the concurrent injection of Abeta1-40. These results indicate that Abeta1-40 protects neurons from Abeta1-42-induced neuronal damage in vitro and in vivo, not by sequestrating metals, but by inhibiting the beta-sheet transformation and fibril formation of Abeta1-42. Our data suggest a mechanism by which elevated Abeta1-42/Abeta1-40 ratio accelerates the development of Alzheimer's disease (AD) in familial AD.     

Replica-exchange molecular dynamics simulation for understanding the initial process of amyloid peptide aggregation

We applied replica-exchange molecular dynamics simulation to five fragments of amyloid-β peptide in order to study the mechanism of amyloid fibril formation. In this study, we calculated the free energy by focusing on how to form the β-structures to obtain the dominant structures. We classify the obtained β-structures and elucidate the order of β-structure assembly.     

Alzheimer's disease Abeta peptide fragment 10-30 forms a spectrum of metastable oligomers with marked preference for N to N and C to C monomer termini proximity

Oligomers of Abeta peptide have been indicated recently as a possible main causative agent of Alzheimer's disease. However, information concerning their structural properties is very limited. Here Abeta oligomers are studied by non-covalent complexes mass spectrometry and disulfide rearrangement. As a model molecule, an Abeta fragment spanning residues 10-30 (Abeta10-30) has been used. This model peptide is known to contain the core region responsible for Abeta aggregation to fibrils. Non-covalent complexes mass spectrometry indicates that, at neutral pH, monomers are accompanied by oligomers up to hexamers of gradually decreasing population. H-2H exchange studies and direct monomer exchange rate measurements with the use of 15N labeled peptides and mass spectrometry show a fast exchange of monomeric units between oligomers. Disulfide exchange studies of cysteine tagged Abeta10-30 and its mutant show proximity of N-N and C-C termini of monomers in oligomers. The presented data underscore a dynamic character for pre-nucleation forms of Abeta, however, with a marked tendency for parallel strand orientation in oligomers.     

Aggregating the amyloid Abeta(11-25) peptide into a four-stranded beta-sheet structure

We present a detailed analysis of the structural properties of one monomer of Abeta(11-25) as well as of the aggregation mechanisms for four chains of Abeta(11-25) using the activation-relaxation technique coupled with a generic energy potential. Starting from a random distribution of these four chains, we find that the system assembles rapidly into a random globular state that evolves into three- and four-stranded antiparallel beta-sheets. The aggregation process is considerably accelerated by the presence of preformed dimers. We also find that the reptation mechanism already identified in shorter peptides plays a significant role here in allowing the structure to reorganize without having to fully dissociate.     

Abeta42 is more rigid than Abeta40 at the C terminus: implications for Abeta aggregation and toxicity

Abeta40 and Abeta42 are the major forms of amyloid beta peptides (Abeta) in the brain. Although Abeta42 differs from Abeta40 by only two residues, Abeta42 is much more prone to aggregation and more toxic to neurons than Abeta40. To probe whether dynamics contribute to such dramatic difference in function, backbone ps-ns dynamics of native Abeta monomers were characterized by 15N spin relaxation at 273.3 K and 800 MHz. Abeta42 aggregates much faster than Abeta40 in the NMR tube. The effect of Abeta aggregation was removed from the relaxation measurement by interleaved data collection. R1, R2 and nuclear Overhauser enhancement (NOE) values are similar in Abeta40 and Abeta42, except at the C terminus, indicating Abeta42 and Abeta40 monomers have identical global motions. Comparisons of the spectral density function J(0.87omegaH) and order parameters (S2) indicate that the Abeta42 C terminus is more rigid than the Abeta40 C terminus. At 280.4 K and 287.6 K, the Abeta42 C terminus remains more rigid than the Abeta40 C terminus, suggesting such a dynamical difference is likely present at the physiological temperature. The Abeta42 monomer likely has less configurational entropy due to restricted motion in the C terminus and may pay a smaller entropic price to form fibrils than the Abeta40 monomer. We hypothesize that the entropic difference between Abeta40 and Abeta42 monomers might partly account for the fact that Abeta42 is the major Abeta species in parenchymal senile plaques in most Alzheimer's diseased brains in spite of the predominance of Abeta40 in plasma. The increased rigidity of the Abeta42 C terminus is likely due to its pre-ordering for beta-conformation present in soluble oligomers and fibrils. The Abeta42 C terminus may therefore serve as an internal seed for aggregation.     

Copper-dependent inhibition of cytochrome c oxidase by Abeta(1-42) requires reduced methionine at residue 35 of the Abeta peptide

By altering key amino acid residues of the Alzheimer's disease-associated amyloid-beta peptide, we investigated the mechanism through which amyloid-beta inhibits cytochrome c oxidase (EC 1.9.3.1). Native amyloid-beta inhibited cytochrome oxidase by up to 65%, and the level of inhibition was determined by the period of amyloid-beta ageing before the cytochrome oxidase assay. Substituting tyrosine-10 with alanine did not affect maximal enzyme inhibition, but the altered peptide required a longer period of ageing. By contrast, oxidizing the sulfur of methionine-35 to a sulfoxide, or substituting methionine-35 with valine, completely abrogated the peptide's inhibitory potential towards cytochrome oxidase. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed that the loss of inhibitory potential towards cytochrome oxidase with the methionine-35-altered peptides did not correlate with a substantially different distribution of amyloid-beta oligomeric species. Although the amyloid-beta-mediated inhibition of cytochrome oxidase was completely dependent on the presence of divalent Cu2+, it was not supported by monovalent Cu+, and experiments with catalase and H2O2 indicated that the mechanism of cytochrome oxidase inhibition does not involve amyloid-beta-mediated H2O2 production. We propose that amyloid-beta-mediated inhibition of cytochrome oxidase is dependent on the peptide's capacity to bind, then reduce Cu2+, and that it may involve the formation of a redox active amyloid-beta-methionine radical.     

The partition and transport behavior of cytotoxic ionic liquids (ILs) through the DPPC bilayer: Insights from molecular dynamics simulation

A molecular dynamics (MD) simulation with atomistic details was performed to examine the partitioning and transport behavior of moderately cytotoxic ionic liquids (ILs), namely choline bis(2-ethylhexyl) phosphate (CBEH), choline bis(2,4,4-trimethylpentyl) phosphinate (CTMP) and choline O,O-diethyl dithiophosphate (CDEP) in a fully hydrated dipalmitoylphosphatidylcholine (DPPC) bilayer in the fluid phase at 323?K. The structure of ILs was so selected to understand if the role of dipole and dispersion forces in the ILs distribution in the membrane can be possible. Several analyses including mass density, electrostatic potential, order parameter, diffusion coefficients and hydrogen bond formation, was carried out to determine the precise location of the anionic species inside the membrane. Moreover, the potential of the mean force (PMF) method was used to calculate free energy profile for transferring anionic species from the DPPC membrane into the bulk water. While less cytotoxic DEP is located within the bulk water, more cytotoxic TMP and BEH ILs were found to remain in the membrane and the energy barrier for crossing through the bilayer center of BEH was higher. Various ILs have no significant effect on P–N vector. The thickness of lipid bilayer decreased in all systems comprising ILs, while area per lipid increased.     

Zinc-induced aggregation of Abeta (10-21) potentiates its action on voltage-gated potassium channel

Zinc may play an important role in the pathogenesis of Alzheimer's disease (AD) through influencing the conformation and neurotoxicity of amyloid beta-proteins (Abeta). Zn(2+) induces rapid aggregation of synthetic or endogenous Abeta in a pH-dependent fashion. Here we show for the first time that Zn(2+)-induced aggregation of Abeta (10-21) potentiates its action on outward potassium currents in hippocampal CA1 pyramidal neurons. Using the whole-cell voltage-clamp technique, we showed that Abeta (10-21) blocked the fast-inactivating outward potassium current (I(A)) in a concentration- and aggregation-dependent manner, but with no effect on the delayed rectifier potassium current (I(K)). Both the unaggregated and aggregated forms of Abeta (10-21) significantly shifted the activation curve and the inactivation curve of I(A) to more negative potentials. But the aggregated form has more effects than the unaggregated form. These data indicated that aggregation of amyloid fragments by zinc ions is required in order to obtain full modulatory effects on potassium channel currents.     

Effect of the Alzheimer amyloid fragment Abeta(25-35) on Akt/PKB kinase and survival of PC12 cells

The phosphatidylinositol 3 kinase (PI3K)-Akt/PKB pathway protects neurons from apoptosis caused by diverse stress stimuli. However, its protective role against the amyloid beta peptide (Abeta), a major constituent of Alzheimer's disease plaques, has not been studied. We investigated the effect of the Abeta-derived Abeta(25-35) peptide on apoptosis and on the Akt survival pathway in PC12 cells. Cells submitted to micromolar concentrations of Abeta(25-35) exhibited increased production of reactive oxygen species (ROS) and morphological alterations consistent with apoptosis. Akt1 was activated shortly after incubation with Abeta(25-35) and Abeta(1-40) with a kinetics different to that of nerve-derived growth factor. Akt1 activation was blocked by the PI3K inhibitor wortmannin. We tested the hypothesis that Akt1 might modify the vulnerability of neural cells to apoptosis induced by Abeta(25-35). Overexpression of an active version of Akt1 attenuated the apoptotic effect of Abeta(25-35) as determined by flow cytometry. Moreover, PC12 cells overexpressing a membrane-targeted N-myristylated fusion protein of enhanced green fluorescence protein (EGFP) and mouse Akt1 exhibited lower levels of ROS than control EGFP-transfected cells. The present findings demonstrate that Akt1 is activated in response to Abeta(25-35) in a PI3K-dependent manner and that active Akt1 protects PC12 cells against the pro-apoptotic action of this peptide.     

Unique physicochemical profile of beta-amyloid peptide variant Abeta1-40E22G protofibrils: conceivable neuropathogen in arctic mutant carriers

A new early-onset form of Alzheimer's disease (AD) was described recently where a point mutation was discovered in codon 693 of the beta-amyloid (Abeta) precursor protein gene, the Arctic mutation. The mutation translates into a single amino acid substitution, glutamic acid-->glycine, in position 22 of the Abeta peptide. The mutation carriers have lower plasma levels of Abeta than normal, while in vitro studies show that Abeta1-40E22G protofibril formation is significantly enhanced. We have explored the nature of the Abeta1-40E22G peptide in more detail, in particular the protofibrils. Using size-exclusion chromatography (SEC) and circular dichroism spectroscopy (CD) kinetic and secondary structural characteristics were compared with other Abeta1-40 peptides and the Abeta12-28 fragment, all having single amino acid substitutions in position 22. We have found that Abeta1-40E22G protofibrils are a group of comparatively stabile beta-sheet-containing oligomers with a heterogeneous size distribution, ranging from >100 kDa to >3000 kDa. Small Abeta1-40E22G protofibrils are generated about 400 times faster than large ones. Salt promotes their formation, which significantly exceeds all the other peptides studied here, including the Dutch mutation Abeta1-40E22Q. Position 22 substitutions had significant effects on aggregation kinetics of Abeta1-40 and in Abeta12-28, although the qualitative aspects of the effects differed between the native peptide and the fragment, as no protofibrils were formed by the fragments. The rank order of protofibril formation of Abeta1-40 and its variants was the same as the rank order of the length of the nucleation/lag phase of the Abeta12-28 fragments, E22V>E22A?E22G>E22Q?E22, and correlated with the degree of hydrophobicity of the position 22 substituent. The molecular mass of peptide monomers and protofibrils were estimated better in SEC studies using linear rather than globular calibration standards. The characteristics of the Abeta1-40E22G suggest an important role for the peptide in the neuropathogenesis in the Arctic form of AD.     

Mutations that reduce aggregation of the Alzheimer's Abeta42 peptide: an unbiased search for the sequence determinants of Abeta amyloidogenesis

The primary component of amyloid plaque in the brains of Alzheimer's patients is the 42 residue amyloid-beta-peptide (Abeta42). Although the amino acid residue sequence of Abeta42 is known, the molecular determinants of Abeta amyloidogenesis have not been elucidated. To facilitate an unbiased search for the sequence determinants of Abeta aggregation, we developed a genetic screen that couples a readily observable phenotype in E. coli to the ability of a mutation in Abeta42 to reduce aggregation. The screen is based on our finding that fusions of the wild-type Abeta42 sequence to green fluorescent protein (GFP) form insoluble aggregates in which GFP is inactive. Cells expressing such fusions do not fluoresce. To isolate variants of Abeta42 with reduced tendencies to aggregate, we constructed and screened libraries of Abeta42-GFP fusions in which the sequence of Abeta42 was mutated randomly. Cells expressing GFP fusions to soluble (non-aggregating) variants of Abeta42 exhibit green fluorescence. Implementation of this screen enabled the isolation of 36 variants of Abeta42 with reduced tendencies to aggregate. The sequences of most of these variants are consistent with previous models implicating hydrophobic regions as determinants of Abeta42 aggregation. Some of the variants, however, contain amino acid substitutions not implicated in pre-existing models of Abeta amyloidogenesis.     

Mutations enhance the aggregation propensity of the Alzheimer's A beta peptide

Aggregation of the amyloid β (Aβ) peptide plays a key role in the molecular etiology of Alzheimer’s disease. Despite the importance of this process, the relationship between the sequence of Aβ and the propensity of the peptide to aggregate has not been fully elucidated. The sequence determinants of aggregation can be revealed by probing the ability of amino acid substitutions (mutations) to increase or decrease aggregation. Numerous mutations that decrease aggregation have been isolated by laboratory-based studies. In contrast, very few mutations that increase aggregation have been reported, and most of these were isolated from rare individuals with early-onset familial Alzheimer’s disease. To augment the limited data set of clinically derived mutations, we developed an artificial genetic screen to isolate novel mutations that increase aggregation propensity. The screen relies on the expression of Aβ-green fluorescent protein fusion in Escherichia coli. In this fusion, the ability of the green fluorescent protein reporter to fold and fluoresce is inversely correlated with the aggregation propensity of the Aβ sequence. Implementation of this screen enabled the isolation of 20 mutant versions of Aβ with amino acid substitutions at 17 positions in the 42-residue sequence of Aβ. Biophysical studies of synthetic peptides corresponding to sequences isolated by the screen confirm the increased aggregation propensity and amyloidogenic behavior of the mutants. The mutations were isolated using an unbiased screen that makes no assumptions about the sequence determinants of aggregation. Nonetheless, all 16 of the most aggregating mutants contain substitutions that reduce charge and/or increase hydrophobicity. These findings provide compelling evidence supporting the hypothesis that sequence hydrophobicity is a major determinant of Aβ aggregation.     

Alpha7-nicotinic acetylcholine receptors mediate an Abeta(1-42)-induced increase in the level of acetylcholinesterase in primary cortical neurones

The beta-amyloid protein (Abeta) is the major protein component of amyloid plaques found in the Alzheimer brain. Although there is a loss of acetylcholinesterase (AChE) from both cholinergic and non-cholinergic neurones in the brain of Alzheimer patients, the level of AChE is increased around amyloid plaques. Previous studies using P19 cells in culture and transgenic mice which overexpress human Abeta have suggested that this increase may be due to a direct action of Abeta on AChE expression in cells adjacent to amyloid plaques. The aim of the present study was to examine the mechanism by which Abeta increases levels of AChE in primary cortical neurones. Abeta1-42 was more potent than Abeta1-40 in its ability to increase AChE in primary cortical neurones. The increase in AChE was unrelated to the toxic effects of the Abeta peptides. The effect of Abeta1-42 on AChE was blocked by inhibitors of alpha7 nicotinic acetylcholine receptors (alpha7 nAChRs) as well as by inhibitors of L- or N-type voltage-dependent calcium channels (VDCCs), whereas agonists of alpha7 nAChRs (choline, nicotine) increased the level of AChE. The results demonstrate that the effect of Abeta1-42 on AChE is due to an agonist effect of Abeta1-42 on the alpha7 nAChR.     

Abeta(31-35) and Abeta(25-35) fragments of amyloid beta-protein induce cellular death through apoptotic signals: Role of the redox state of methionine-35

In order to clarify the basis of neuronal toxicity exerted by the shortest active peptides of amyloid beta-protein (Abeta), the toxic effects of Abeta(31-35) and Abeta(25-35) peptides on isolated rat brain mitochondria were investigated. The results show that exposure of isolated rat brain mitochondria to Abeta(31-35) and Abeta(25-35) peptides determines: (i) release of cytochrome c; (ii) mitochondrial swelling and (iii) a significant reduction in mitochondrial oxygen consumption. In contrast, the amplitude of these events resulted attenuated in isolated brain mitochondria exposed to the Abeta(31-35)Met35(OX) in which methionine-35 was oxidized to methionine sulfoxide. The Abeta peptide derivative with norleucine substituting Met-35, i.e., Abeta(31-35)Nle-35, had not effect on any of the biochemical parameters tested. We have further characterized the action of Abeta(31-35) and Abeta(25-35) peptides on neuronal cells. Taken together our result indicate that Abeta(31-35) and Abeta(25-35) peptides in non-aggregated form, i.e., predominantly monomeric, are strongly neurotoxic, having the ability to enter within the cells, determining mitochondrial damage with an evident trigger of apoptotic signals. Such a mechanism of toxicity seems to be dependent by the redox state of methionine-35.     

Molecular dynamics studies of hexamers of amyloid-beta peptide (16-35) and its mutants: influence of charge states on amyloid formation

To study the early stage of amyloid-beta peptide (Abeta) aggregation, hexamers of the wild-type (WT) Abeta(16-35) and its mutants with amyloid-like conformations have been studied by molecular dynamics simulations in explicit water for a total time of 1.7 micros. We found that the amyloid-like structures in the WT oligomers are destabilized by the solvation of ionic D23/K28 residues, which are buried in the fibrils. This means that the desolvation of D23/K28 residues may contribute to the kinetic barrier of aggregation in the early stage. In the E22Q/D23N, D23N/K28Q, and E22Q/D23N/K28Q mutants, hydration becomes much less significant because the mutated residues have neutral amide side-chains. These amide side-chains can form linear cross-strand hydrogen bond chains, or "polar zippers", if dehydrated. These "polar zippers" increase the stability of the amyloid-like conformation, reducing the barrier for the early-stage oligomerization. This is in accord with experimental observations that both the D23/K28 lactamization and the E22Q/D23N mutation promote aggregation. We also found that the E22Q/D23N mutant prefers an amyloid-like conformation that differs from the one found for WT Abeta. This suggests that different amyloid structures may be formed under different conditions.     

Specificity in protein-DNA interactions: energetic recognition by the (cytosine-C5)-methyltransferase from HhaI

Sequence-specific interactions between proteins and DNA are essential for a variety of biological functions. The (cytosine-C5)-methyltransferase from HhaI (M.HhaI) specifically modifies the second base in GCGC sequences, employing a base flipping mechanism to access the target base being chemically modified. The mechanism of sequence-specific recognition of M.HhaI is not evident based on crystallographic structures, leading to the suggestion that recognition is linked to the flipping event itself, a process that may be referred to as energetic recognition. Using computational methods, it is shown that the free energy barriers to flipping are significantly higher in non-cognate versus the cognate sequence, supporting the energetic recognition mechanism. Energetic recognition is imparted by two protein "selectivity filters" that function via a "web" of protein-DNA interactions in short-lived, high energy states present along the base flipping pathway. Other sequence-specific DNA binding proteins whose function involves significant distortion of DNA's conformation may use a similar recognition mechanism.     

Folding and membrane insertion of amyloid‐beta (25–35) peptide and its mutants: Implications for aggregation and neurotoxicity

The mechanisms of interfacial folding and membrane insertion of the Alzheimer's amyloid‐β fragment Aβ(25–35) and its less toxic mutant, N27A‐Aβ(25–35) and more toxic mutant, M35A‐Aβ(25–35), are investigated using replica–exchange molecular dynamics in an implicit water‐membrane environment. This study simulates the processes of interfacial folding and membrane insertion in a spontaneous fashion to identify their general mechanisms. Aβ(25–35) and N27A‐Aβ(25–35) peptides share similar mechanisms: the peptides are first located in the membrane hydrophilic region where their C‐terminal residues form helical structures. The peptides attempt to insert themselves into the membrane hydrophobic region using the C‐terminal or central hydrophobic residues. A small portion of peptides can successfully enter the membrane's hydrophobic core, led by their C‐terminal residues, through the formation of continuous helical structures. No detectable amount of M35A‐Aβ(25–35) peptides appeared to enter the membrane's hydrophobic core. The three studied peptides share a similar helical structure for their C‐terminal five residues, and these residues mainly buried within the membrane's hydrophobic region. In contrast, their N‐terminal properties are markedly different. With respect to the Aβ(25–35), the N27A‐Aβ(25–35) forms a more structured helix and is buried deeper within the membrane, which may result in a lower degree of aggregation and a lower neurotoxicity; in contrast, the less structured and more water‐exposed M35A‐Aβ(25–35) is prone to aggregation and has a higher neurotoxicity. Understanding the mechanisms of Aβ peptide interfacial folding and membrane insertion will provide new insights into the mechanisms of neurodegradation and may give structure‐based clues for rational drug design preventing amyloid associated diseases. Proteins 2010. © 2010 Wiley‐Liss, Inc.