Insights into the oxygen-based ligand of the low pH component of the Cu(2+)-amyloid-β complex

An N-terminal acidic β-sheet domain is responsible for the metal-accumulation properties of amyloid-β protofibrils: a molecular dynamics study

The influence of metal ions on the structure of amyloid- β (Aβ) protofibril models was studied through molecular dynamics to explore the molecular mechanisms underlying metal-induced Aβ aggregation relevant in Alzheimer's disease (AD). The models included 36-, 48-, and 188-mers of the Aβ42 sequence and two disease-modifying variants. Primary structural effects were observed at the N-terminal domain, as it became susceptible to the presence of cations. Specially when β-sheets predominate, this motif orients N-terminal acidic residues toward one single face of the β-sheet, resulting in the formation of an acidic region that attracts cations from the media and promotes the folding of the N-terminal region, with implications in amyloid aggregation. The molecular phenotype of the protofibril models based on Aβ variants shows that the AD-causative D7N mutation promotes the formation of N-terminal β-sheets and accumulates more Zn2+, in contrast to the non-amyloidogenic rodent sequence that hinders the β-sheets and is more selective for Na+ over Zn2+ cations. It is proposed that forming an acidic β-sheet domain and accumulating cations is a plausible molecular mechanism connecting the elevated affinity and concentration of metals in Aβ fibrils to their high content of β-sheet structure at the N-terminal sequence.

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.

Copper Binding Induces Polymorphism in Amyloid-β Peptide: Results of Computational Models

Amyloid-β (Aβ) peptides are intrinsically disordered peptides, and their aggregation is the hallmark of Alzheimer's disease development. The propensity of the Aβ peptide to intermolecular interactions, the latter favoring different types of oligomers and aggregated forms, has been the object of a huge number of studies. Several facts are now established: the presence of large amount of d-block (M) ions (Zn, Cu, and Fe) in the aggregated forms; the 1:1 M/Aβ ratio favors the formation of amorphous aggregates, with an aggregation rate lower than that in the absence of such ions. In particular, statistical models describing the interactions between copper and amyloid peptides are mandatory to explain the relationship between neurodegeneration, copper dyshomeostasis, and overproduction of reactive oxygen species, the latter event occurring with aging. In this work, we show, by replica-exchange molecular dynamics simulations, that a copper ion (Cu²⁺) bound as in the experimentally observed prevailing coordination enhances the probability of closed structures that hinder the formation of extended intermolecular hydrogen bonds that stabilize fibrillar ordered aggregated forms. On the other hand, this effect enhances the catalytic role of the complex during the lifetime of soluble forms.

Identification of key structural features of the elusive Cu-Aβ complex that generates ROS in Alzheimer's disease

Oxidative stress is linked to the etiology of Alzheimer's disease (AD), the most common cause of dementia in the elderly. Redox active metal ions such as copper catalyze the production of Reactive Oxygen Species (ROS) when bound to the amyloid-β (Aβ) peptide encountered in AD. We propose that this reaction proceeds through a low-populated Cu-Aβ state, denoted the "catalytic in-between state" (CIBS), which is in equilibrium with the resting state (RS) of both Cu(i)-Aβ and Cu(ii)-Aβ. The nature of this CIBS is investigated in the present work. We report the use of complementary spectroscopic methods (X-ray absorption spectroscopy, EPR and NMR) to characterize the binding of Cu to a wide series of modified peptides in the RS. ROS production by the resulting Cu-peptide complexes was evaluated using fluorescence and UV-vis based methods and led to the identification of the amino acid residues involved in the Cu-Aβ CIBS species. In addition, a possible mechanism by which the ROS are produced is also proposed. These two main results are expected to affect the current vision of the ROS production mechanism by Cu-Aβ but also in other diseases involving amyloidogenic peptides with weakly structured copper binding sites.

Dioxygen activation in the Cu-amyloid β complex

We investigate, by means of density-functional theory, the binding of dioxygen to Cu(I)-amyloid β (Aβ), one of the first steps in the oxidation of ascorbate by dioxygen. Cu, Aβ, ascorbate and dioxygen are all present in the synapse during neurodegeneration, when the above species can trigger an irreversible oxidative stress inducing the eventual death of neurons. The binding of dioxygen to Cu(I) is possible and its role in dioxygen activation of Cu ligands and of residues in the first coordination sphere is described in atomic detail. Dioxygen is activated when a micro-environment suitable for a square-planar Cu(2+) coordination is present and a negatively charged group like Asp 1 carboxylate takes part in the Cu coordination anti to O2.

Ligand–metal-drug coordination based micelles for efficient intracellular doxorubicin delivery

A ligand–metal-drug coordination architecture is exploited to construct polymeric micelles with the high efficient loading and pH-triggered release of anticancer drug.