3D Structures
and Redox Potentials of Cu<sup>2+</sup>–Aβ(1–16)
Complexes at Different pH: A Computational
Study
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Abstract
Oxidative
stress induced by redox-active metal cations such as
Cu<sup>2+</sup> is a key event in the development of Alzheimer’s
disease. A detailed knowledge of the structure of Cu<sup>2+</sup>–Aβ
complex is thus important to get a better understanding of this critical
process. In the present study, we use a computational approach that
combines homology modeling with quantum-mechanics-based methods to
determine plausible 3D structures of Cu<sup>2+</sup>–Aβ(1–16)
complexes that enclose the different metal coordination spheres proposed
experimentally at different pH values. With these models in hand,
we determine their standard reduction potential (SRP) with the aim
of getting new insights into the relation between the structure of
these complexes and their redox behavior. Results show that in all
cases copper reduction induces CO<sub>backbone</sub> decoordination,
which, for distorted square planar structures in the oxidized state
(Ia_δδ, IIa_εδε, IIa_εεε,
and IIc_ε), leads to tricoordinated species. For the pentacoordinated
structural candidate Ib_δε with Glu11 at the apical position,
the reduction leads to a distorted tetrahedral structure. The present
results highlight the importance of the nature of the ligands on the
SRP. The computed values (with respect to the standard hydrogen electrode)
for complexes enclosing negatively charged ligands in the coordination
sphere (from −0.81 to −0.12 V) are significantly lower
than those computed for models involving neutral ligands (from 0.19
to 0.28 V). Major geometry changes induced by reduction, on both the
metal site and the peptide configuration, are discussed as well as
their possible influence in the formation of reactive oxygen species