Hydrogen peroxide can be generated by tau in the presence of Cu(II)

https://doi.org/10.1016/j.bbrc.2007.04.191Get rights and content

Abstract

Alzheimer’s disease has been closely related with oxidative stress, which might be responsible for the dysfunction or death of neuronal cells that contributes to disease pathogenesis. Impaired copper homeostasis makes contribution to the oxidative stress and consequently to several neurodegenerative conditions. Inappropriate binding of Cu(II) to cellular proteins are currently being explored as sources of pathological oxidative stress in several neurodegenerative disorders. Here we report that a fragment of tau protein possesses copper reduction activity and initiates the copper-mediated generation of hydrogen peroxide. The tau peptide was found to be oxidized to form disulfide bond-linked dimer. The hydrogen peroxide generated was quantified by TCEP/DTNB (tris(2-carboxyethyl) phosphine hydrochloride/5,5′-dithio-bis(2-nitrobenzoic acid). Since the copper reduction capacity and the generation of hydrogen peroxide were believe to be a major toxicological pathway of Aβ peptide, the functional similarity shared by tau and Aβ implies a new perspective of tau pathology.

Section snippets

Materials and methods

Peptide synthesis. R2 peptide was synthesized on Fmoc-Wang resin by means of the standard Fmoc/tBu strategy and O-benzotriazol-N,N,N′,N′-tetramethyluronium hexafluorophosphate/1-hydroxybenzotriazol (HBTU/HOBt) protocol [21]. The peptide and all protecting groups were cleaved from the resin with TFA containing phenol (5%), thioanisole (5%), ethanedithiol (2.5%), and water (5%) for 120 min [22]. The crude peptide was purified by reverse phase HPLC using an ODS-UG-5 column (Develosil) with a linear

R2 is capable of reducing copper

We first analyzed the copper reduction capacity of R2 peptide. R2 peptide, ascorbic acid (as a positive control) and BSA (as a negative control) were co-incubated with copper ions at 37 °C for 30 min. Cu(I) formation was monitored by using BC, which formed a complex with Cu(I), showing an absorbance at 480 nm. Results indicate that R2 peptide showed copper reduction capacity, though weaker than ascorbic acid, a strong reducing agent (Fig. 1). In the same experiments, BSA showed hardly any copper

Discussion

Our work clearly demonstrated that copper can be reduced by tau peptide and can catalyze tau peptide oxidation. However, iron, another redox-active metal ion, is incapable of catalyzing tau oxidation. This is different from Aβ peptide, which can reduce both copper and iron and may generate hydrogen peroxide in the presence of either of them [7], [10]. This could be attributed to the different affinity of tau with these two metals. It has been reported that copper may bind tightly with tau

Acknowledgments

The authors appreciate the financial support from the National Natural Science Foundation of China (Nos. 20532020 and 20672067), and the Program for Changjiang Scholars and Innovative Research Team in University (PCSIRT, IRT0404).

References (29)

  • J.C. Han et al.

    A procedure for quantitative determination of tris(2-carboxyethyl)phosphine, an odorless reducing agent more stable and effective than dithiothreitol

    Anal. Biochem.

    (1994)
  • J. Han et al.

    Quantitation of hydrogen peroxide using tris(2-carboxyethyl)phosphine

    Anal. Biochem.

    (1996)
  • E. Mandelkow

    Alzheimer’s disease. The tangled tale of tau

    Nature

    (1999)
  • K.J. Barnham et al.

    Neurodegenerative diseases and oxidative stress

    Nat. Rev. Drug Discov.

    (2004)
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