ИСТИНА

Amyloid-β (Aβ) is a 39-42 amino acid long peptide found in the cerebrospinal fluid. Aggregation of Aβ plays a key role in Alzheimer’s disease (AD). Details of the molecular mechanism underlying that pathological aggregation still remain unclear. It is widely accepted that metals such as zinc and copper may play a critical role in the Aβ aggregation. Aβ is known to interact with Zn(II) and Cu(II) ions through its metal-binding domain composed of N-terminal residues 1-16 (Aβ16). Due to the presence of the single Tyr residue at the position 10 of the amino acid chain (Tyr-10), Aβ peptides render themselves for electrochemical analysis since the accessibility of Tyr-10 for electrochemical oxidation on the electrode surface can alter upon peptide aggregation and/or complexing with the metal ions [1]. Electrochemical oxidation of the synthetic peptides Aβ16 and Aβ42 was investigated on carbon screen printed electrodes. The Aβ16 and Aβ42 oxidation signals determined by the oxidation of Tyr-10 at the potential of about 0.6-0.7 V (vs. Ag/AgCl) were used for monitoring peptide interactions with metal ions and its aggregation in vitro. Addition of both Zn(II) and Cu(II) ions significantly reduced the intensity of the Aβ16 oxidation current and shifted the peak to more positive potentials, while Mg(II) and Ca(II) ions had no noticeable effect. Substitution of two His residues at positions 6 and 13 by Ala in Aβ16 dramatically changed its electrochemical oxidation signal and behavior in the presence of Zn(II) ions. Compare to Aβ16, the oxidation signal of H6A-H13A-Aβ16 was about 2.5 times smaller and increased with the concentration of Zn(II) ions. Aβ16 mutants with a single amino acid substitution E11K or a modification such as phosphorylation of Ser-8 demonstrated the electrooxidation peaks differing in an amplitude and their own behavior toward Zn(II) ions. Aβ42 aggregation reduced the peptide oxidation peak that is associated with a lesser accessibility of Tyr-10 for the electrochemical reaction upon peptide aggregation. Correlation between the intensity of Aβ42 oxidation signal and the mean size of aggregates measured by the dynamic light scattering was found. The proposed electrochemical assay based on the direct oxidation signal of Tyr-10 appears to be very promising for monitoring the metal-induced conformational changes and aggregation of Aβ peptides in vitro and can potentially be used in screening of drug candidates for the treatment of AD. This work was financially supported by the Russian Ministry of Education and Science (Contract No. 14.604.21.0074, ID RFMEFI60414X0074). [1] E.V. Suprun, N.V. Zaryanov, S.P. Radko, A.A. Kulikova, S.A. Kozin, A.A. Makarov, A.I. Archakov, V.V. Shumyantseva, Tyrosine Based Electrochemical Analysis of Amyloid-β Fragment (1-16) Binding to Metal(II) Ions, Electrochim. Acta (2015), http://dx.doi.org/10.1016/j.electacta.2015.01.066