Zinc(II) Binding Site to the Amyloid-β Peptide: Insights from Spectroscopic Studies with a Wide Series of Modified Peptides

Preparation and Characterization of Zn(II)-Stabilized Aβ42 Oligomers

Aβ oligomers are being investigated as cytotoxic agents in Alzheimer's disease (AD). Because of their transient nature and conformational heterogeneity, the relationship between the structure and activity of these oligomers is still poorly understood. Hence, methods for stabilizing Aβ oligomeric species relevant to AD are needed to uncover the structural determinants of their cytotoxicity. Here, we build on the observation that metal ions and metabolites have been shown to interact with Aβ, influencing its aggregation and stabilizing its oligomeric species. We thus developed a method that uses zinc ions, Zn(II), to stabilize oligomers produced by the 42-residue form of Aβ (Aβ42), which is dysregulated in AD. These Aβ42-Zn(II) oligomers are small in size, spanning the 10-30 nm range, stable at physiological temperature, and with a broad toxic profile in human neuroblastoma cells. These oligomers offer a tool to study the mechanisms of toxicity of Aβ oligomers in cellular and animal AD models.

Divalent metal ion modulation of a simple peptide-based hydrogel: self-assembly and viscoelastic properties

Peptide self-assembly has been highly studied to understand the pathways in forming higher order structures along with the development and application of resulting hydrogel materials. Driven by noncovalent interactions, peptide hydrogels are stimuli-responsive to any addition to its gelling conditions. Here, a Phe-His based peptide, C14-FH(Trt)-OH, was synthesized and characterized with 1H NMR, FT-IR, MS, UV-vis spectroscopies and elemental analysis. Based on SEM imaging, the dipeptide conjugate was capable of forming a nanofibrous, interconnected network encapsulating buffer to produce a supramolecular hydrogel. Through the addition of Zn2+ and Cu2+, there is a clear change in the self-assembled nanostructures characterized through SEM. With this effect on self-assembly follows a change in the viscoelastic properties of the material, as determined through rheological frequency sweeps, with 2 and 3 orders of magnitude decreases in the elastic modulus G' in the presence of Zn2+ and Cu2+ respectively. This highlights the tunability of soft material properties with peptide design and self-assembly, through metal ions and Nδ-directed coordination.

Rationally Designed Cu(I) Ligand to Prevent CuAβ-Generated ROS Production in the Alzheimer's Disease Context

In the context of Alzheimer's disease, copper (Cu) can be loosely bound to the amyloid-β (Aβ) peptide, leading to the formation of CuAβ, which can catalytically generate reactive oxygen species that contribute to oxidative stress. To fight against this phenomenon, the chelation therapy approach has been developed and consists of using a ligand able to remove Cu from Aβ and to redox-silence it, thus stopping the reactive oxygen species (ROS) production. A large number of Cu(II) chelators has been studied, allowing us to define and refine the properties required to design a "good" ligand, but without strong therapeutic outcomes to date. Those chelators targeted the Cu(II) redox state. Herein, we explore a parallel and relevant alternative pathway by designing a chelator able to target the Cu(I) redox state. To that end, we designed LH2 ([1N3S] binding set) and demonstrated that (i) it is perfectly able to extract Cu(I) from Cu(I)Aβ even in the presence of an excess of Zn(II) and (ii) it redox-silences the Cu, preventing the formation of ROS. We showed that LH2 that is sensitive to oxidation can efficiently replace the [Zn(II)L] complex without losing its excellent ability to stop the ROS production while increasing its resistance to oxidation.

Silver nanoparticle-based SERS sensors for sensitive detection of amyloid-β aggregates in biological fluids

One of the hallmarks of Alzheimer's disease (AD) pathogenesis is the production, aggregation, and deposition of amyloid-β (Aβ) peptide. Surface-enhanced Raman spectroscopy (SERS) is a promising analytical technique capable of providing valuable information on chemical composition and molecule conformations in biological samples. However, one of the main challenges for introducing the SERS technique into the practice is preparation of scalable and at the same time stable nanostructured sensors with uniform spatial distribution of nanoparticles. Herein, we propose SERS platforms for reproducible, sensitive, label-free quantification of amyloid-β aggregates for short-wavelength - 532 and 633 nm - lasers. A SERS sensor - based on silver nanoparticles immobilized into a chitosan film (AgNP/CS) - provided a uniform distribution of AgNPs from a colloidal suspension across the SERS sensor, resulting in nanomolar limits of detection (LODs) for Aβ42 aggregates with a portable 532 nm laser. The laser-induced deposition was used to obtain denser periodic plasmonic sensors (AgNP/LID) with a uniform nanoparticle distribution. The AgNP/LID SERS sensor allowed for 15 pM LOD for Aβ42 aggregates with 633 nm laser. Notably, both nanostructured substrates allowed to distinguish amyloid aggregates from monomers. Therefore, our approach demonstrated applicability of SERS for detection of macromolecular volumetric objects as amyloid-β aggregates for fundamental biological studies as well as for "point-of-care" diagnostics and screening for early stages of neurodegenerative diseases.

Concentration Effect, Structural Properties, and Driving Force on Aβ28 Dimerization with and without Zn2+ Cooperation: Learning from Replica Exchange Sampling

Zn²⁺ is a very important factor in promoting the formation of amyloid beta (Aβ) aggregates and amyloid plaques. The Zn²⁺ -bound Aβ species generate amorphous or low molecular-weight oligomers. However, it is a lack of studies to approach the starting structural features (dimerization) in Aβ nucleation processes with and without Zn²⁺ , which is the key point in understanding Zn²⁺ -induced nucleation mechanisms. To better understand the effect of concentration, structural properties, and the driving force, 14 independent replica exchange molecular dynamics simulations were performed in Aβ₂₈ dimerization with and without Zn²⁺ (zAβ₂₈ ) cooperation. Our scanning results show that the aggregation propensity is easier in Aβ₂₈ -Aβ₂₈ and Aβ₂₈ -zAβ₂₈ systems than zAβ₂₈ -zAβ₂₈ system. In binding property, the Aβ₂₈ -Aβ₂₈ model (-61.5 kcal mol^-1 ) is stronger than zAβ₂₈ -zAβ₂₈ (-26.6 kcal mol^-1 ) and Aβ₂₈ -zAβ₂₈ (-7.24 kcal mol^-1 ) models. Further analysis confirmed that H13 and H14 residues play specific roles in the three systems. The key point is the orientation of N atom of the imidazole ring in histidine residues. Furthermore, we discovered different driving forces for each system. Our current study contributes to the understanding of how the Aβ₂₈ dimer interacts with Zn²⁺ , which could lead to new insights into Zn²⁺ -induced nucleation mechanisms.

The pathomimetic oAβ25–35 model of Alzheimer's disease: Potential for screening of new therapeutic agents

Alzheimer's disease (AD) is the most common form of dementia in the elderly, currently affecting more than 40 million people worldwide. The two main histopathological hallmarks of AD were identified in the 1980s: senile plaques (composed of aggregated amyloid-β (Aβ) peptides) and neurofibrillary tangles (composed of hyperphosphorylated tau protein). In the human brain, both Aβ and tau show aggregation into soluble and insoluble oligomers. Soluble oligomers of Aβ include their most predominant forms - Aβ_1-40 and Aβ_1-42 - as well as shorter peptides such as Aβ_25-35 or Aβ_25-35/40. Most animal models of AD have been developed using transgenesis, based on identified human mutations. However, these familial forms of AD represent less than 1% of AD cases. In this context, the idea emerged in the 1990s to directly inject the Aβ_25-35 fragment into the rodent brain to develop an acute model of AD that could mimic the disease's sporadic forms (99% of all cases). This review aims to: (1) summarize the biological activity of Aβ_25-35, focusing on its impact on the main structural and functional alterations observed in AD (cognitive deficits, APP misprocessing, tau system dysfunction, neuroinflammation, oxidative stress, cholinergic and glutamatergic alterations, HPA axis dysregulation, synaptic deficits and cell death); and (2) confirm the interest of this pathomimetic model in AD research, as it has helped identify and characterize many molecules (marketed, in clinical development, and in preclinical testing), and to the development of alternative approaches for AD prevention and therapy. Today, the Aβ_25-35 model appears as a first-intent choice model to rapidly screen the symptomatic or neuroprotective potencies of new compounds, chemical series, or innovative therapeutic strategies.

Current understanding of metal-dependent amyloid-β aggregation and toxicity

The discovery of effective therapeutics targeting amyloid-β (Aβ) aggregates for Alzheimer's disease (AD) has been very challenging, which suggests its complicated etiology associated with multiple pathogenic elements. In AD-affected brains, highly concentrated metals, such as copper and zinc, are found in senile plaques mainly composed of Aβ aggregates. These metal ions are coordinated to Aβ and affect its aggregation and toxicity profiles. In this review, we illustrate the current view on molecular insights into the assembly of Aβ peptides in the absence and presence of metal ions as well as the effect of metal ions on their toxicity.

The co-effect of copper and lipid vesicles on Aβ aggregation

Both metal ions and lipid membranes have a wide distribution in amyloid plaques and play significant roles in AD pathogenesis. Although influences of different metal ions or lipid vesicles on the aggregation of Aβ peptides have been extensively studied, their combined effects are less understood. In this study, we reported a unique effect of copper ion on Aβ aggregation in the presence of lipid vesicles, different from other divalent metal ions. Cu²⁺ in a super stoichiometric amount leads to the rapid formation of β-sheet rich structure, containing abundant low molecular weight (LMW) oligomers. We demonstrated that oligomerization of Aβ40 induced by Cu²⁺ binding was an essential prerequisite for the rapid conformation transition. Overall, the finding provided a new view on the complex triple system of Aβ, copper ion and lipid vesicles, which might help understanding of Aβ pathologies.

Molecular Structure of Cu(II)-Bound Amyloid-β Monomer Implicated in Inhibition of Peptide Self-Assembly in Alzheimer's Disease

Metal ions, such as copper and zinc ions, have been shown to strongly modulate the self-assembly of the amyloid-β (Aβ) peptide into insoluble fibrils, and elevated concentrations of metal ions have been found in amyloid plaques of Alzheimer's patients. Among the physiological transition metal ions, Cu(II) ions play an outstanding role since they can trigger production of neurotoxic reactive oxygen species. In contrast, structural insights into Cu(II) coordination of Aβ have been challenging due to the paramagnetic nature of Cu(II). Here, we employed specifically tailored paramagnetic NMR experiments to determine NMR structures of Cu(II) bound to monomeric Aβ. We found that monomeric Aβ binds Cu(II) in the N-terminus and combined with molecular dynamics simulations, we could identify two prevalent coordination modes of Cu(II). For these, we report here the NMR structures of the Cu(II)-bound Aβ complex, exhibiting heavy backbone RMSD values of 1.9 and 2.1 Å, respectively. Further, applying aggregation kinetics assays, we identified the specific effect of Cu(II) binding on the Aβ nucleation process. Our results show that Cu(II) efficiently retards Aβ fibrillization by predominately reducing the rate of fibril-end elongation at substoichiometric ratios. A detailed kinetic analysis suggests that this specific effect results in enhanced Aβ oligomer generation promoted by Cu(II). These results can quantitatively be understood by Cu(II) interaction with the Aβ monomer, forming an aggregation inert complex. In fact, this mechanism is strikingly similar to other transition metal ions, suggesting a common mechanism of action of retarding Aβ self-assembly, where the metal ion binding to monomeric Aβ is a key determinant.

Sequence-Activity Relationship of ATCUN Peptides in the Context of Alzheimer's Disease

Amino-terminal Cu^II and Ni^II (ATCUN) binding sequences are widespread in the biological world. Here, we report on the study of eight ATCUN peptides aimed at targeting copper ions and stopping the associated formation of reactive oxygen species (ROS). This study was actually more focused on Cu(Aβ)-induced ROS production in which the Aβ peptide is the "villain" linked to Alzheimer's disease. The full characterization of Cu^II binding to the ATCUN peptides, the Cu^II extraction from Cu^II(Aβ), and the ability of the peptides to prevent and/or stop ROS formation are described in the relevant biological conditions. We highlighted in this research that all the ATCUN motifs studied formed the same thermodynamic complex but that the addition of a second histidine in position 1 or 2 allowed for an improvement in the Cu^II uptake kinetics. This kinetic rate was directly related to the ability of the peptide to stop the Cu^II(Aβ)-induced production of ROS, with the most efficient motifs being HWHG and HGHW.

Why the Ala-His-His Peptide Is an Appropriate Scaffold to Remove and Redox Silence Copper Ions from the Alzheimer's-Related Aβ Peptide

The progressive, neurodegenerative Alzheimer's disease (AD) is the most widespread dementia. Due to the ageing of the population and the current lack of molecules able to prevent or stop the disease, AD will be even more impactful for society in the future. AD is a multifactorial disease, and, among other factors, metal ions have been regarded as potential therapeutic targets. This is the case for the redox-competent Cu ions involved in the production of reactive oxygen species (ROS) when bound to the Alzheimer-related Aβ peptide, a process that contributes to the overall oxidative stress and inflammation observed in AD. Here, we made use of peptide ligands to stop the Cu(Aβ)-induced ROS production and we showed why the AHH sequence is fully appropriate, while the two parents, AH and AAH, are not. The AHH peptide keeps its beneficial ability against Cu(Aβ)-induced ROS, even in the presence of ZnII-competing ions and other biologically relevant ions. The detailed kinetic mechanism by which AHH could exert its action against Cu(Aβ)-induced ROS is also proposed.

Neglected N-Truncated Amyloid-β Peptide and Its Mixed Cu-Zn Complexes

Amyloid-β (Aβ) peptides are involved in Alzheimer's disease (AD) development. The interactions of these peptides with copper and zinc ions also seem to be crucial for this pathology. Although Cu(II) and Zn(II) ions binding by Aβ peptides has been scrupulously investigated, surprisingly, this phenomenon has not been so thoroughly elucidated for N-truncated Aβ_4-x-probably the most common version of this biomolecule. This negligence also applies to mixed Cu-Zn complexes. From the structural in silico analysis presented in this work, it appears that there are two possible mixed Cu-Zn(Aβ_4-x) complexes with different stoichiometries and, consequently, distinct properties. The Cu-Zn(Aβ_4-x) complex with 1:1:1 stoichiometry may have a neuroprotective superoxide dismutase-like activity. On the other hand, another mixed 2:1:2 Cu-Zn(Aβ_4-x) complex is perhaps a seed for toxic oligomers. Hence, this work proposes a novel research direction for our better understanding of AD development.

A Dual-Pronged Approach: A Ruthenium(III) Complex That Modulates Amyloid-β Aggregation and Disrupts Its Formed Aggregates

Alzheimer's disease (AD) is a devastating neurological disorder for which soluble oligomers of the peptide amyloid-β (Aβ) are now recognized as the neurotoxic species. Metal-based therapeutics are uniquely suited to target Aβ, with ruthenium-based (Ru) complexes emerging as propitious candidates. Recently, azole-based Ru(III) complexes were observed to modulate the aggregation of Aβ in solution, where the inclusion of a primary amine proximal to the ligand coordination site improved the activity of the complexes. To advance these structure-activity relationships, a series of oxazole-based Ru complexes were prepared and evaluated for their ability to modulate Aβ aggregation. From these studies, a lead candidate, Oc, emerged that had superior activity relative to its azole predecessors in modulating the aggregation of soluble Aβ and diminishing its cytotoxicity. Further evaluation of Oc demonstrated its ability to disrupt formed Aβ aggregates, resulting in smaller amorphous species. Because altering both sides of the aggregation equilibrium for Aβ has not been previously suggested for metal-based complexes for AD, this work represents an exciting new avenue for improved therapeutic success.

Amyloid-beta–copper interaction studied by simultaneous nitrogen K and copper L2,3-edge soft X-ray absorption spectroscopy

We study the interaction between amyloid β (Aβ) peptides and Cu and Zn metal ions by using soft X-ray absorption spectroscopy. The spectral features of the peptides and Cu are simultaneously characterized by recording spectra at the N K-edge and at the Cu L_2,3-edges. In the presence of the peptides, the Cu L_2,3-edge shows a fingerprint of monovalent Cu(I), caused by the interaction with the peptides. The appearance of Cu(I) is less significant at an acidic pH than at a basic pH. Furthermore, aggregation leads to a smaller signature of Cu(I). N K-edge spectra reveal that Cu and Zn ions exhibit a different coordination with the nitrogen atoms in the peptides. This suggests different roles of Cu and Zn in the peptide aggregation. Our work provides physical insight into the participation of the metal ions and Aβ in the toxic reactive oxygen species formation.

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Amyloid-beta–copper interaction leads to distinct X-ray spectroscopic signatures

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After interaction monovalent copper(I) is found

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The X-ray signatures strongly depend on the pH and incubation conditions

Zinc induced structural changes in the intrinsically disordered BDNF Met prodomain confer synaptic elimination

Human brain derived neurotrophic factor (BDNF) encodes a protein product consisting of a C-terminal mature domain (mature BDNF) and an N-terminal prodomain, which is an intrinsically disordered protein. A common single nucleotide polymorphism in humans results in a methionine substitution for valine at position 66 of the prodomain, and is associated with memory deficits, depression and anxiety disorders. The BDNF Met66 prodomain, but not the Val66 prodomain, promotes rapid structural remodeling of hippocampal neurons' growth cones and dendritic spines by interacting directly with the SorCS2 receptor. While it has been reported that the Met66 and Val66 prodomains exhibit only modest differences in structural propensities in the apo state, here we show that Val66 and Met66 prodomains differentially bind zinc (Zn). Zn2+ binds with higher affinity and more broadly impacts residues on the Met66 prodomain compared to the Val66 prodomain as shown by NMR and ITC. Zn2+ binding to the Met66 and Val66 prodomains results in distinct conformational and macroscopic differences observed by NMR, light scattering and cryoEM. To determine if Zn2+ mediated conformational change in the Met66 prodomain is required for biological effect, we mutated His40, a Zn2+ binding site, and observed a loss of Met66 prodomain bioactivity. As the His40 site is distant from the known region of the prodomain involved in receptor binding, we suggest that Met66 prodomain bioactivity involves His40 mediated stabilization of the multimeric structure. Our results point to the necessity of a Zn2+-mediated higher order molecular assembly of the Met66 prodomain to mediate neuronal remodeling.

Probing the acetylcholinesterase inhibitory activity of a novel Ru(II) polypyridyl complex and the supramolecular interaction by (STD)-NMR

Currently, acetylcholinesterase (AChE) inhibitors are the only anti-Alzheimer drugs commercially available. Despite their wide use those drugs are all dose dependent and their effect last for no longer than two years, with several side effects. The search of novel acetylcholinesterase (AChE) inhibitors remains as the main scientific route. Here we describe the synthesis, characterization, biological activity and an NMR binding-target study of a novel cis-[Ru(Bpy)₂(EtPy)₂]²⁺, (RuEtPy), Bpy = 2,2'-bipyridine and EtPy = 4,2-Ethylamino-pyridine) as a potential AChE inhibitor. The classic Ellman's colorimetric assay suggests that the RuEtPy exhibits a high inhibitory activity, following a competitive mechanism, with a remarkable low inhibition constant (Ki ≈ 16.8 μM), together with a IC₅₀ = 39 μM. Hence, we have studied the spatial interactions for this novel candidate towards the human acetylcholinesterase (hAChE) using saturation transfer difference (STD)-NMR, in order to describe the mechanism of the interaction. NMR binding-target results shows that the 4,2-Ethylamino-Pyridine group is spatially closer to hAChE surface chemical arrangement than 2,2' bipyridine counterpart, exerting an efficient intermolecular interaction, with a low dissociation constant (K_D ≈ 55 μM), probing that 4,2-Ethylamino-pyridine motif plays a key role in the inhibitory action.

Forcefield evaluation and accelerated molecular dynamics simulation of Zn(II) binding to N-terminus of amyloid-β

We report conventional and accelerated molecular dynamics simulation of Zn(II) bound to the N-terminus of amyloid-β. By comparison against NMR data for the experimentally determined binding mode, we find that certain combinations of forcefield and solvent model perform acceptably in describing the size, shape and secondary structure, and that there is no appreciable difference between implicit and explicit solvent models. We therefore used the combination of ff14SB forcefield and GBSA solvent model to compare the result of different binding modes of Zn(II) to the same peptide, using accelerated MD to enhance sampling and comparing the free peptide simulated in the same way. We show that Zn(II) imparts significant rigidity to the peptide, disrupts the secondary structure and pattern of salt bridges seen in the free peptide, and induces closer contact between residues. Free energy surfaces in 1 or 2 dimensions further highlight the effect of metal coordination on peptide's spatial extent. We also provide evidence that accelerated MD provides improved sampling over conventional MD by visiting as many or more configurations in much shorter simulation times.

Modulation of amyloid-β aggregation by metal complexes with a dual binding mode and their delivery across the blood-brain barrier using focused ultrasound

One of the key hallmarks of Alzheimer's disease is the aggregation of the amyloid-β peptide to form fibrils. Consequently, there has been great interest in studying molecules that can disrupt amyloid-β aggregation. While a handful of molecules have been shown to inhibit amyloid-β aggregation in vitro, there remains a lack of in vivo data reported due to their inability to cross the blood-brain barrier. Here, we investigate a series of new metal complexes for their ability to inhibit amyloid-β aggregation in vitro. We demonstrate that octahedral cobalt complexes with polyaromatic ligands have high inhibitory activity thanks to their dual binding mode involving π-π stacking and metal coordination to amyloid-β (confirmed via a range of spectroscopic and biophysical techniques). In addition to their high activity, these complexes are not cytotoxic to human neuroblastoma cells. Finally, we report for the first time that these metal complexes can be safely delivered across the blood-brain barrier to specific locations in the brains of mice using focused ultrasound.

Degradation of Alzheimer's Amyloid-β by a Catalytically Inactive Insulin-Degrading Enzyme

It is known that insulin-degrading-enzyme (IDE) plays a crucial role in the clearance of Alzheimer's amyloid-β (Aβ). The cysteine-free IDE mutant (cf-E111Q-IDE) is catalytically inactive against insulin, but its effect on Aβ degradation is unknown that would help in the allosteric modulation of the enzyme activity. Herein, the degradation of Aβ(1-40) by cf-E111Q-IDE via a non-chaperone mechanism is demonstrated by NMR and LC-MS, and the aggregation of fragmented peptides is characterized using fluorescence and electron microscopy. cf-E111Q-IDE presented a reduced effect on the aggregation kinetics of Aβ(1-40) when compared with the wild-type IDE. Whereas LC-MS and diffusion ordered NMR spectroscopy revealed the generation of Aβ fragments by both wild-type and cf-E111Q-IDE. The aggregation propensities and the difference in the morphological phenotype of the full-length Aβ(1-40) and its fragments are explained using multi-microseconds molecular dynamics simulations. Notably, our results reveal that zinc binding to Aβ(1-40) inactivates cf-E111Q-IDE's catalytic function, whereas zinc removal restores its function as evidenced from high-speed AFM, electron microscopy, chromatography, and NMR results. These findings emphasize the catalytic role of cf-E111Q-IDE on Aβ degradation and urge the development of zinc chelators as an alternative therapeutic strategy that switches on/off IDE's function.

Helix-coil transition and conformational deformity in Aβ42-monomer: a case study using the Zn2+ cation

The metal ions (like Fe2+, Zn²⁺, Cu2+) are known to influence the amyloid beta (Aβ) aggregation. In this study, we have examined the conformational and dynamical changes during the coordination of Aβ-monomer with the Zn2+ ion using all-atom molecular dynamics (MD) simulations using explicit solvent models. We have probed the unfolding of the full-length Aβ₄₂ monomer both inclusive and exclusive of the Zn2+ cation, with 1:1 ratio of the peptide and the Zn2+ cation. The inclusion of the Zn2+ cation shows differential intra-peptide interactions which has been probed using various analyses. The Helix - Coil transition of the wild type Aβ42 monomer is studied using the steered molecular dynamics simulations by taking the end-to-end C-α distance across the peptide. This gives an idea of the unequal intra - peptide and peptide - water interactions being found across the length of the Aβ monomer. The transition of an α-helix dominated wild-type (WT) Aβ structure to the unfolded coil structure gives significant evidence of the intra-peptide hydrogen bonding shifts in the presence of the Zn2+ cation. This accounts for the structural and the dynamical variations that take place in the Aβ monomer in the presence of the Zn2+ cation to mimic the conditions/environment at the onset of fibrillation.Communicated by Ramaswamy H. Sarma.

Amyloid Oligomers: A Joint Experimental/Computational Perspective on Alzheimer's Disease, Parkinson's Disease, Type II Diabetes, and Amyotrophic Lateral Sclerosis

Protein misfolding and aggregation is observed in many amyloidogenic diseases affecting either the central nervous system or a variety of peripheral tissues. Structural and dynamic characterization of all species along the pathways from monomers to fibrils is challenging by experimental and computational means because they involve intrinsically disordered proteins in most diseases. Yet understanding how amyloid species become toxic is the challenge in developing a treatment for these diseases. Here we review what computer, in vitro, in vivo, and pharmacological experiments tell us about the accumulation and deposition of the oligomers of the (Aβ, tau), α-synuclein, IAPP, and superoxide dismutase 1 proteins, which have been the mainstream concept underlying Alzheimer's disease (AD), Parkinson's disease (PD), type II diabetes (T2D), and amyotrophic lateral sclerosis (ALS) research, respectively, for many years.

Evaluating the Multifunctionality of a New Modulator of Zinc-Induced Aβ Aggregation Using a Novel Computational Approach

The high concentration of zinc metal ions in Aβ aggregations is one of the most cited hallmarks of Alzheimer's disease (AD), and several substantial pieces of evidence emphasize the key role of zinc metal ions in the pathogenesis of AD. In this study, while designing a multifunctional peptide for simultaneous targeting Aβ aggregation and chelating the zinc metal ion, a novel and comprehensive approach is introduced for evaluating the multifunctionality of a multifunctional drugs based on computational methods. The multifunctional peptide consists of inhibitor and chelator domains, which are included in the C-terminal hydrophobic region of Aβ, and the first four amino acids of human albumin. The ability of the multifunctional peptide in zinc ion chelation has been investigated using molecular dynamics (MD) simulations of the peptide-zinc interaction for 300 ns, and Bennett's acceptance ratio (BAR) method has been used to accurately calculate the chelation free energy. Data analysis demonstrates that the peptide chelating domain can be stably linked to the zinc ion. Besides, the introduced method used for evaluating chelation and calculating the free energy of peptide binding to zinc ions was successfully validated by comparison with previous experimental and theoretical published data. The results indicate that the multifunctional peptide, coordinating with the zinc metal ion, can be effective in Aβ inhibition by preserving the native helical structure of the Aβ₄₂ monomer as well as disrupting the β-sheet structure of Aβ₄₂ aggregates. Detailed assessments of the Aβ₄₂-peptide interactions elucidate that the inhibition of Aβ is achieved by considerable hydrophobic interactions and hydrogen bonding between the multifunctional peptide and the hydrophobic Aβ regions, along with interfering in stable bridges formed inside the Aβ aggregate.

Impact of sphingosine and acetylsphingosines on the aggregation and toxicity of metal-free and metal-treated amyloid-β

Pathophysiological shifts in the cerebral levels of sphingolipids in Alzheimer's disease (AD) patients suggest a link between sphingolipid metabolism and the disease pathology. Sphingosine (SP), a structural backbone of sphingolipids, is an amphiphilic molecule that is able to undergo aggregation into micelles and micellar aggregates. Considering its structural properties and cellular localization, we hypothesized that SP potentially interacts with amyloid-β (Aβ) and metal ions that are found as pathological components in AD-affected brains, with manifesting its reactivity towards metal-free Aβ and metal-bound Aβ (metal–Aβ). Herein, we report, for the first time, that SP is capable of interacting with both Aβ and metal ions and consequently affects the aggregation of metal-free Aβ and metal–Aβ. Moreover, incubation of SP with Aβ in the absence and presence of metal ions results in the aggravation of toxicity induced by metal-free Aβ and metal–Aβ in living cells. As the simplest acyl derivatives of SP, N-acetylsphingosine and 3-O-acetylsphingosine also influence metal-free Aβ and metal–Aβ aggregation to different degrees, compared to SP. Such slight structural modifications of SP neutralize its ability to exacerbate the cytotoxicity triggered by metal-free Aβ and metal–Aβ. Notably, the reactivity of SP and the acetylsphingosines towards metal-free Aβ and metal–Aβ is determined to be dependent on their formation of micelles and micellar aggregates. Our overall studies demonstrate that SP and its derivatives could directly interact with pathological factors in AD and modify their pathogenic properties at concentrations below and above critical aggregation concentrations.

The reactivity of sphingosine and acetylsphingosines towards both metal-free and metal-treated amyloid-β is demonstrated showing a correlation of their micellization properties.

Emergence of Barrel Motif in Amyloid-β Trimer: A Computational Study

Amyloid-β (Aβ) peptides form assemblies that are pathological hallmarks of Alzheimer's disease. Aβ oligomers are soluble, mobile, and toxic forms of the peptide that act in the extracellular space before assembling into protofibrils and fibrils. Therefore, oligomers play an important role in the mechanism of Alzheimer's disease. Since it is difficult to determine by experiment the atomic structures of oligomers, which accumulate fast and are polymorphic, computer simulation is a useful tool to investigate elusive oligomers' structures. In this work, we report extended all-atom molecular dynamics simulations, both canonical and replica exchange, of Aβ(1-42) trimer starting from two different initial conformations: (i) the pose produced by the best docking of a monomer aside of a dimer (simulation 1), representing oligomers freshly formed by assembling monomers, and (ii) a configuration extracted from an experimental mature fibril structure (simulation 2), representing settled oligomers in equilibrium with extended fibrils. We showed that in simulation 1, regions with small β-barrels are populated, indicating the chance of spontaneous formation of domains resembling channel-like structures. These structural domains are alternative to those more representative of mature fibrils (simulation 2), the latter showing a stable bundle of C-termini that is not sampled in simulation 1. Moreover, trimer of Aβ(1-42) can form internal pores that are large enough to be accessed by water molecules and Ca2+ ions.

Binding of Cu2+ to Aβ1-29 causes aggregation and toxicity in SH-SY5Y cells

The accumulation and aggregation of amyloid-β (Aβ) are critical factors in the pathogenesis of Alzheimer's disease (AD). Several studies have indicated that metal ions such as Cu²⁺and Zn²⁺ play a key role in the formation and stabilization of neurotoxic Aβ aggregates, however the molecular mechanisms underlying Aβ cytotoxicity have not yet been fully elucidated. Previously, we showed that the Aβ-derived fragment peptide (Aβ-FrP), Aβ1-19, altered conformation in the presence of Cu²⁺, inhibiting its digestion by metalloproteinase-7 (MMP-7). In this study we demonstrated that Aβ1-19 did not form aggregates in the presence of Cu²⁺. Therefore, we synthesized a new Aβ-FrP, Aβ1-29, which displayed Cu²⁺-dependent conformational conversion and aggregate formation. Aβ1-29 was cleaved by MMP-7, however this reaction was inhibited in the presence of Cu²⁺ in a similar way to Aβ1-19. Interestingly, Aβ1-29 showed conformational conversion and aggregate formation in the presence of Zn²⁺, however this did not confer resistance against MMP-7 cleavage. Moreover, Aβ1-29 induced the apoptotic cell death of neural SH-SY5Y cells in the presence of Cu²⁺ but not Zn²⁺. These results suggest that Cu²⁺, unlike Zn²⁺, may play an important role in the aggregation mechanism of Aβ and thus in the pathology of AD.

Ruthenium(III) complexes with imidazole ligands that modulate the aggregation of the amyloid-β peptide via hydrophobic interactions

Alzheimer's disease (AD) is the most common form of dementia, characterized by extracellular protein deposits, comprised primarily of the peptide amyloid-beta (Aβ), are a pathological indicator of the disease. Commonly known as Aβ plaques, these deposits contain a relatively high concentration of metals, making metallotherapeutics uniquely suited to target soluble Aβ, thereby limiting its aggregation and cytotoxicity. Ruthenium-based complexes are promising candidates for advancement, as the complex PMRU20 (2-aminothiazolium [trans-RuCl₄(2-aminothiazole)₂]) and several thiazole-based derivatives were found to prevent the aggregation of Aβ, with hydrogen-bonding functional groups improving their performance. Further investigation into the impact of the heteroatom in the azole ring on the activity of Ru complexes was achieved through the synthesis and evaluation of a small set of imidazole-based compounds. The ability of the complexes to prevent the aggregation of Aβ was determined where the same sample was subjected to analysis by three complementary methods: ThT fluorescence, dynamic light scattering (DLS), and transmission electron microscopy (TEM). It was found that hydrophobic interactions, along with hydrogen-bonding via the imidazole nitrogen heteroatom, promoted interactions with the Aβ peptide, thereby limiting its aggregation. Furthermore, it was found that having rapid and sequential exchange proved detrimental as it resulted in a decreased association with Aβ. These results highlight important considerations between a balance of intermolecular interactions and ligand exchange kinetics in the design of further therapeutic candidates.

Lead discovery of a guanidinyl tryptophan derivative on amyloid cascade inhibition

Amyloid cascade, one of pathogenic pathways of Alzheimer’s disease (AD), was focused as one of drug discovery targets. In this study, β-secretase (BACE1) inhibitors were designed aiming at the development of multifunctional compounds targeting amyloid pathogenic cascade. Tryptophan was used as a core structure due to its properties of the central nervous system (CNS) penetration and BACE1 inhibition activity. Three amino acid residues and guanidine were selected as linkers to connect the tryptophan core structure and the extended aromatic moieties. The distance between the aromatic systems of the core structure and the extended moieties was kept at the optimal length for amyloid-β (Aβ) peptide binding to inhibit its fibrillation and aggregation. Sixteen designed compounds were evaluated in silico. Eight hit compounds of TSR and TGN series containing serine and guanidine linkers, respectively, were identified and synthesized based on docking results. TSR2 and TGN2 were found to exert strong actions as BACE1 (IC50 24.18 µM and 22.35 µM) and amyloid aggregation inhibitors (IC50 37.06 µM and 36.12 µM). Only TGN2 demonstrated a neuroprotective effect in SH-SY5Y cells by significantly reducing Aβ-induced cell death at a concentration of 2.62 µM. These results support the validity of multifunctional approaches to inhibition of the β-amyloid cascade.

Role of PTA in the prevention of Cu(amyloid-β) induced ROS formation and amyloid-β oligomerisation in the presence of Zn

Metal-targeting drugs are being widely explored as a possible treatment for Alzheimer's disease, but most of these ligands are developed to coordinate Cu(ii). In a previous communication (E. Atrián-Blasco, E. Cerrada, A. Conte-Daban, D. Testemale, P. Faller, M. Laguna and C. Hureau, Metallomics, 2015, 7, 1229-1232) we showed another strategy where Cu(i) was targeted with the PTA (1,3,5-triaza-7-phosphaadamantane) ligand that is able to target Cu(ii) as well, reduce it and keep it in a safe complexed species. Removal of Cu(ii) from the amyloid-β peptide prevents the stabilization of oligomers and protofibrils and the complexation of Cu(i) also stops the formation of reactive oxygen species. Besides, zinc, which is found in the synaptic cleft at a higher concentration than copper, can hamper the ability of metal-targeting drug candidates, an issue that is still poorly considered and studied. Here we show that PTA fully retains the above described properties even in the presence of zinc, thus fulfilling an additional pre-requisite for its use as a model of Cu(i)-targeting drug candidates in the Alzheimer's disease context.

Ruthenium(iii) complexes containing thiazole-based ligands that modulate amyloid-β aggregation

Alzheimer's Disease (AD) is a devastating neurodegenerative disorder where one of the commonly observed pathological hallmarks is extracellular deposits of the peptide amyloid-β (Aβ). These deposits contain a high concentration of metals and initially presented a promising target for therapy; however it has become increasingly evident that the soluble form of the peptide is neurotoxic, not the amyloidogenic species. Metal-based therapeutics are uniquely suited to target soluble Aβ and have shown considerable promise to prevent the aggregation and induced cytotoxicity of the peptide in vitro. Herein, we have prepared a small series of derivatives of two promising Ru(iii) complexes NAMI-A (imidazolium [trans-RuCl₄(1H-imidazole)(dimethyl sulfoxide-S)]) and PMRU20 (2-aminothiazolium [trans-RuCl₄(2-aminothiazole)₂]), to determine structure-activity relationships (SAR) for Ru(iii) therapeutics for AD. Using the three complementary methods of Thioflavin T fluorescence, dynamic light scattering (DLS), and transmission electron microscopy (TEM), it was determined that the symmetry around the metal center did not significantly impact the activity of the complexes, but rather the attached thiazole ligand(s) mitigated Aβ aggregation. Across both families of Ru(iii) complexes the determined SAR for the functional groups on the thiazole ligands to modulate Aβ aggregation were NH₂ > CH₃ > H. These results highlight the importance of secondary interactions between the metallotherapeutic and the Aβ peptide where hydrogen-bonding has the greatest impact on modulating Aβ aggregation.

Reactivities of cyclam derivatives with metal–amyloid-β

New examples of azamacrocyclic metal chelators that modulate the interactions between metal ions and Aβ and the reactivities of metal–Aβ were developed under criteria based on structural and functional variations on the backbone of Cyclam.

Structural Insights Into TDP-43 and Effects of Post-translational Modifications

Transactive response DNA binding protein (TDP-43) is a key player in neurodegenerative diseases. In this review, we have gathered and presented structural information on the different regions of TDP-43 with high resolution structures available. A thorough understanding of TDP-43 structure, effect of modifications, aggregation and sites of localization is necessary as we develop therapeutic strategies targeting TDP-43 for neurodegenerative diseases. We discuss how different domains as well as post-translational modification may influence TDP-43 overall structure, aggregation and droplet formation. The primary aim of the review is to utilize structural insights as we develop an understanding of the deleterious behavior of TDP-43 and highlight locations of established and proposed post-translation modifications. TDP-43 structure and effect on localization is paralleled by many RNA-binding proteins and this review serves as an example of how structure may be modulated by numerous compounding elements.

Identification of a Novel Multifunctional Ligand for Simultaneous Inhibition of Amyloid-Beta (Aβ42) and Chelation of Zinc Metal Ion

Zinc binding to β-amyloid structure could promote amyloid-β aggregation, as well as reactive oxygen species (ROS) production, as suggested in many experimental and theoretical studies. Therefore, the introduction of multifunctional drugs capable of chelating zinc metal ion and inhibiting Aβ aggregation is a promising strategy in the development of AD treatment. The present study has evaluated the efficacy of a new bifunctional peptide drug using molecular docking and molecular dynamics (MD) simulations. This drug comprises two different domains, an inhibitor domain, obtained from the C-terminal hydrophobic region of Aβ, and a Zn²⁺ chelating domain, derived from rapeseed meal, merge with a linker. The multifunctionality of the ligand was evaluated using a comprehensive set of MD simulations spanning up to 3.2 μs including Aβ relaxation, ligand-Zn²⁺ bilateral interaction, and, more importantly, ligand-Zn²⁺-Aβ₄₂ trilateral interactions. Analysis of the results strongly indicated that the bifunctional ligand can chelate zinc metal ion and avoid Aβ aggregation simultaneously. The present study illustrated that the proposed ligand has considerable hydrophobic interactions and hydrogen bonding with monomeric Aβ in the presence of zinc metal ion. Therefore, in light of these considerable interactions and contacts, the α-helical structure of Aβ has been enhanced, while the β-sheet formation is prevented and the α-helix native structure is protected. Furthermore, the analysis of interactions between Aβ and ligand-zinc complex revealed that the zinc metal ion is coordinated to Met13, the ending residue of the ligand and merely one residue in Aβ. The results have proven the previous experimental and theoretical findings in the literature about Aβ interactions with zinc metal ion and also Aβ interactions with the first domain of the proposed ligand. Moreover, the current research has evaluated the chelation using MD simulation and linear interaction energy (LIE) methods, and the result has been satisfactorily verified with previous experimental and theoretical (DFT) studies.

Glial S100A6 Degrades β-amyloid Aggregation through Targeting Competition with Zinc Ions

Evidence has been accumulating that zinc ions can trigger β-amyloid (Aβ) deposition and senile plaque formation in the brain, a pathological hallmark of Alzheimer's disease (AD). Chelating zinc inhibits Aβ aggregation and may hold promise as a therapeutic strategy for AD. S100A6 is an acidic Ca²⁺/Zn²⁺-binding protein found only in a small number of astrocytes in the normal brain. However, in the AD brain, S100A6 is highly expressed in astrocytes around Aβ plaques. The role of the astrocytic S100A6 upregulation in AD is unknown. In the present study, we examined the effects of S100A6 on Aβ plaques and intracellular zinc levels in a mouse model of AD. Chronic exposure to zinc increased Aβ deposition and S100A6 expression, both reversible by the zinc chelator clioquinol, in the brains of amyloid precursor protein/presenilin 1 (APP/PS1) transgenic mice. To examine whether exogenous S100A6 could induce Aβ plaque disaggregation through competition for zinc in vitro, we incubated APP/PS1 mouse brain sections with recombinant human S100A6 protein or co-incubated them with human S100A6-expressing cells. Both treatments efficiently reduced the Aβ plaque burden in situ. In addition, treatment with exogenous S100A6 protected cultured COS-7 cells against zinc toxicity. Our results show for the first time that increased S100A6 levels correlate with both Aβ disaggregation and decrease of Aβ plaque-associated zinc contents in brain sections with AD-like pathology. Astrocytic S100A6 in AD may protect from Aβ deposition through zinc sequestration.

Effects of Metal Ions on Aβ42 Peptide Conformations from Molecular Simulation Studies

In this study, we investigate the conformational characteristics of full-length Aβ₄₂ peptide monomers in the presence of Na⁺ and Zn²⁺ metal ions using atomistic molecular dynamics (MD) simulations with an aim to explore the possible driving forces behind enhanced aggregation rates of the peptides in the presence of salts. The calculations reveal that the presence of metal ions shifts the conformational equilibrium more toward the compact ordered Aβ structures. Such compact ordered structures stabilized by distant nonlocal contacts between two crucial hydrophobic segments, hp1 and hp2, primarily through two important hydrophobic aromatic residues, Phe-19 and Phe-20, are expected to trigger the aggregation process at a faster rate by populating and stabilizing the aggregation prone structures. Formation of a significant number of such distant contacts in the presence of Na⁺ ions has also been found to result in breaking of the N-terminal helix. On the contrary, binding of Zn²⁺ ion to Aβ peptide is highly specific, which stabilizes the N-terminal helix instead of breaking it. This explains why the aggregation rate of Aβ peptides is higher in the presence of divalent Zn²⁺ ions than monovalent Na⁺ ions. Relatively higher overall stability of the most populated Aβ peptide monomers in the presence of Zn²⁺ ions has been found to be associated with specific Zn²⁺-Aβ binding and significant free energy gain.

Transition Metal Ion Interactions with Disordered Amyloid-β Peptides in the Pathogenesis of Alzheimer's Disease: Insights from Computational Chemistry Studies

Monomers and oligomers of the amyloid-β peptide aggregate to form the fibrils found in the brains of Alzheimer's disease patients. These monomers and oligomers are largely disordered and can interact with transition metal ions, affecting the mechanism and kinetics of amyloid-β aggregation. Due to the disordered nature of amyloid-β, its rapid aggregation, as well as solvent and paramagnetic effects, experimental studies face challenges in the characterization of transition metal ions bound to amyloid-β monomers and oligomers. The details of the coordination chemistry between transition metals and amyloid-β obtained from experiments remain debated. Furthermore, the impact of transition metal ion binding on the monomeric or oligomeric amyloid-β structures and dynamics are still poorly understood. Computational chemistry studies can serve as an important complement to experimental studies and can provide additional knowledge on the binding between amyloid-β and transition metal ions. Many research groups conducted first-principles calculations, ab initio molecular dynamics simulations, quantum mechanics/classical mechanics simulations, and classical molecular dynamics simulations for studying the interplay between transition metal ions and amyloid-β monomers and oligomers. This review summarizes the current understanding of transition metal interactions with amyloid-β obtained from computational chemistry studies. We also emphasize the current view of the coordination chemistry between transition metal ions and amyloid-β. This information represents an important foundation for future metal ion chelator and drug design studies aiming to combat Alzheimer's disease.

Johann-type laboratory-scale x-ray absorption spectrometer with versatile detection modes

We present a low-cost laboratory X-ray absorption spectrometer that uses a conventional X-ray tube source and bent Johann-type crystal monochromators. The instrument is designed for X-ray absorption spectroscopy studies in the 4-20 keV range which covers most K edges of 3d transition metals and L edges of 5d transition metals and actinides. The energy resolution is typically in the range of 1-5 eV at 10 keV depending on the crystal analyser and the Bragg angle. Measurements can be performed in transmission, fluorescence, and imaging modes. Due to its simple and modular design, the spectrometer can be modified to accommodate additional equipment and complex sample environments required for in situ studies. A showcase of various applications is presented.

A catalytic antioxidant for limiting amyloid-beta peptide aggregation and reactive oxygen species generation

Alzheimer's disease (AD) is a multifaceted disease that is characterized by increased oxidative stress, metal-ion dysregulation, and the formation of intracellular neurofibrillary tangles and extracellular amyloid-β (Aβ) aggregates. In this work we report the large affinity binding of the iron(iii) 2,17-bis-sulfonato-5,10,15-tris(pentafluorophenyl)corrole complex FeL1 to the Aβ peptide (K d ∼ 10-7) and the ability of the bound FeL1 to act as a catalytic antioxidant in both the presence and absence of Cu(ii) ions. Specific findings are that: (a) an Aβ histidine residue binds axially to FeL1; (b) that the resulting adduct is an efficient catalase; (c) this interaction restricts the formation of high molecular weight peptide aggregates. UV-Vis and electron paramagnetic resonance (EPR) studies show that although the binding of FeL1 does not influence the Aβ-Cu(ii) interaction (K d ∼ 10-10), bound FeL1 still acts as an antioxidant thereby significantly limiting reactive oxygen species (ROS) generation from Aβ-Cu. Overall, FeL1 is shown to bind to the Aβ peptide, and modulate peptide aggregation. In addition, FeL1 forms a ternary species with Aβ-Cu(ii) and impedes ROS generation, thus showing the promise of discrete metal complexes to limit the toxicity pathways of the Aβ peptide.

Cu and Zn interactions with Aβ peptides: consequence of coordination on aggregation and formation of neurotoxic soluble Aβ oligomers

The coordination chemistry of transition metal ions (Fe, Cu, Zn) with the amyloid-β (Aβ) peptides has attracted a lot of attention in recent years due to its repercussions in Alzheimer's disease (AD).

Strategies Employing Transition Metal Complexes To Modulate Amyloid-β Aggregation

Aggregation of amyloid-β (Aβ) peptides is implicated in the development of Alzheimer's disease (AD), the most common type of dementia. Thus, numerous efforts to identify chemical tactics to control the aggregation pathways of Aβ peptides have been made. Among them, transition metal complexes as a class of chemical modulators against Aβ aggregation have been designed and utilized. Transition metal complexes are able to carry out a variety of chemistry with Aβ peptides (e.g., coordination chemistry and oxidative and proteolytic reactions for peptide modifications) based on their tunable characteristics, including the oxidation state of and coordination geometry around the metal center. This Viewpoint illustrates three strategies employing transition metal complexes toward modulation of Aβ aggregation pathways (i.e., oxidation and hydrolysis of Aβ as well as coordination to Aβ), along with some examples of such transition metal complexes. In addition, proposed mechanisms for three reactivities of transition metal complexes with Aβ peptides are discussed. Our greater understanding of how transition metal complexes have been engineered and used for alteration of Aβ aggregation could provide insight into the new discovery of chemical reagents against Aβ peptides found in AD.

Monitoring metal-amyloid-β complexation by a FRET-based probe: design, detection, and inhibitor screening

A FRET-based method was developed for monitoring metal–amyloid-β complexation and identifying inhibitors against such interaction.

Aggregation of amyloidogenic peptides could cause the onset and progression of neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. These amyloidogenic peptides can coordinate to metal ions, including Zn(ii), which can subsequently affect the peptides' aggregation and toxicity, leading to neurodegeneration. Unfortunately, the detection of metal–amyloidogenic peptide complexation has been very challenging. Herein, we report the development and utilization of a probe (A-1) capable of monitoring metal–amyloid-β (Aβ) complexation based on Förster resonance energy transfer (FRET). Our probe, A-1, is composed of Aβ_1–21 grafted with a pair of FRET donor and acceptor capable of providing a FRET signal upon Zn(ii) binding even at nanomolar concentrations. The FRET intensity of A-1 increases upon Zn(ii) binding and decreases when Zn(ii)-bound A-1 aggregates. Moreover, as the FRET intensity of Zn(ii)-added A-1 is drastically changed when their interaction is disrupted, A-1 can be used for screening a chemical library to determine effective inhibitors against metal–Aβ interaction. Eight natural products (out of 145 compounds; >80% inhibition) were identified as such inhibitors in vitro, and six of them could reduce Zn(ii)–Aβ-induced toxicity in living cells, suggesting structural moieties useful for inhibitor design. Overall, we demonstrate the design of a FRET-based probe for investigating metal–amyloidogenic peptide complexation as well as the feasibility of screening inhibitors against metal-bound amyloidogenic peptides, providing effective and efficient methods for understanding their pathology and finding therapeutic candidates against neurodegenerative disorders.

Metal Binding to Aβ Peptides Inhibits Interaction with Cytochrome c: Insights from Abiological Constructs

Aβ(1-40) peptide is mutated to introduce cysteine residue to allow formation of organized self-assembled monolayers (SAMs) on Au electrodes. Three mutants of this peptide are produced, which vary in the position of the inserted cysteine residue. Fourier transform infrared data on these peptide SAMs show the presence of both α helices and β sheet in these Aβ constructs. These peptide constructs interact with cytochrome c (Cytc), allowing electron transfer between Cytc and the electrode via the Aβ peptides. Binding of metals like Zn2+ or Cu2+ induces changes in the morphologies of these assemblies, making them fold, which inhibits their spontaneous interaction with Cytc.

Mutations of Histidine 13 to Arginine and Arginine 5 to Glycine Are Responsible for Different Coordination Sites of Zinc(II) to Human and Murine Peptides

Because mice and rats do not naturally develop Alzheimer's disease, genetically modified animals are required to study this pathology. This striking difference in terms of disease onset could be due to three alterations in the murine sequence (R5G, Y10F and H13R) of the amyloid-β peptide with respect to the human counterpart. Whether the metal-ion binding properties of the murine peptide are at the origin of such different amyloidogenicity of the two peptides is still an open question. Herein, the main zinc binding site to the murine amyloid-β at physiological pH has been determined through the combination of several spectroscopic and analytical methods applied to a series of six peptides with one or two of the key mutations. These results have been compared with the zinc binding site encountered in the human peptide. A coordination mechanism that demonstrates the importance of the H13R and R5G mutations in the different zinc environments present in the murine and human peptides is proposed. The nature of the minor zinc species present at physiological pH is also suggested for both peptides. Finally, the biological relevance and fallouts of the differences determined in zinc binding to human versus murine amyloid-β are also discussed.