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

Abstract

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 selfassembly, where the metal ion binding to monomeric Aβ is a key determinant.

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

“…Especially, the Cu 2 + and Zn 2 + have been demonstrated to dramatically regulate the selfassembly of the Aβ peptide into insoluble fibrils. [10] Generally, metal-bound species generate amorphous or low molecularweight oligomers which has highly polymorphic features and varied neurotoxicity. [11] According to the observation of high concentration of zinc in AD associated plaques, [12] zinc plays an important role in plaques formations.…”

“…[8d,17] The majority of theoretical studies indicate that H6, E11, H13, and H14 are the main binding sites of Zn 2 + at the N-terminus of Aβ. [17a,c,18] NMR spectroscopy [19] was in experiments to determine the binding structure of Zn 2 + to Aβ (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16). Furthermore, our previous study found that Zn 2 + can have a strong effect on the structural and hydrophobic properties of Aβ.…”

“…As the results, elevated amounts of metal ions have been detected in Aβ plaques of AD patients. Especially, the Cu 2+ and Zn 2+ have been demonstrated to dramatically regulate the self‐assembly of the Aβ peptide into insoluble fibrils [10] . Generally, metal‐bound species generate amorphous or low molecular‐weight oligomers which has highly polymorphic features and varied neurotoxicity [11] .…”

Structural Dynamics of Amyloid-β Protofibrils and Actions of Anti-Amyloid-β Antibodies as Observed by High-Speed Atomic Force Microscopy

“…This energy landscape changes shape depending on the environment surrounding the amyloid molecules. It has been shown that cofactors, including the interaction of amyloid aggregates with lipid membranes, − the effect of metal ions, ,− and interactions with other types of amyloid molecules, can lead to a variety of structural dynamics of the amyloid molecules. HS-AFM is an effective tool for visualizing the effects of cofactors.…”

Chasing the Elusive “In‐Between” State of the Copper‐Amyloid β Complex by X‐ray Absorption through Partial Thermal Relaxation after Photoreduction

“…Indeed, since Aβ1−16 very well reproduces the coordination of Cu(II) and Cu(I) to Aβ1−42, Aβ1−40 and Aβ1−28, it is often used as a model for the longer peptide. [15,26,27] It is well known that, in the physical conditions of standard XAS experiments, which are typically performed at a temperature as low as 10 K, a progressive reduction of Cu(II) to Cu(I) is observed in the Cu-Aβ1−42 peptide complex in vitro.…”