Thermo-Stable Nature of Aromatic Monoamine-Dependent Superoxide-Generating Activity of Human Prion-Derived Cu-Binding Peptides (original) (raw)
Related papers
Objectives: Studies have proposed two opposing roles for copper-bound forms of prion protein (PrP) as an anti-oxidant supporting the neuronal functions and as a pro-oxidant leading to neurodegenerative process involving the generation of reactive oxygen species. The aim of this study is to test the hypothesis in which putative copper-binding peptides derived from PrP function as possible catalysts for monoamine-dependent conversion of hydrogen peroxide to superoxide in vitro. Materials and methods: Four peptides corresponding to the copper (II)-binding motifs in PrP were synthesized and used for analysis of peptide-catalyzed generation of superoxide in the presence of Cu (II) and other factors naturally present in the neuronal tissues. Results: Among the Cu-binding peptides tested, the amino acid sequence corresponding to the Cu-binding site in the helical region was shown to be the most active for superoxide generation in the presence of Cu(II), hydrogen peroxide and aromatic monoamines, known precursors or intermediates of neurotransmitters. Among monoamines tested, three compounds namely phenylethylamine, tyramine and benzylamine were shown to be good substrates for superoxide-generating reactions by the Cu-bound helical peptide. Conclusions: Possible roles for these reactions in development of prion disease were suggested.
Previously, generation of superoxide anion (O2 •-) catalyzed by Cu-binding peptides derived from human prion protein (model sequence for helical Cu-binding motif VNITKQHTVTTTT was most active) in the presence of catecholamines and related aromatic monoamines such as phenylethylamine and tyramine, has been reported [Kawano, T., Int J Biol Sci 2007; 3: 57-63]. The peptide sequence (corresponding to helix 2) tested here is known as threonine-rich neurotoxic peptide. In the present article, the redox behaviors of aromatic monoamines, 20 amino acids and prion-derived tyrosine-rich peptide sequences were compared as putative targets of the oxidative reactions mediated with the threonine-rich prion-peptide. For detection of O2 •-, an O2 •-specific chemiluminescence probe, Cypridina luciferin analog was used. We found that an aromatic amino acid, tyrosine (structurally similar to tyramine) behaves as one of the best substrates for the O2 •-generating reaction (conversion from hydrogen peroxide) catalyzed by Cu-bound prion helical peptide. Data suggested that phenolic moiety is required to be an active substrate while the presence of neither carboxyl group nor amino group was necessarily required. In addition to the action of free tyrosine, effect of two tyrosine-rich peptide sequences YYR and DYEDRYYRENMHR found in human prion corresponding to the tyrosine-rich region was tested as putative sub-strates for the threonine-rich neurotoxic peptide. YYR motif (found twice in the Y-rich region) showed 2-to 3-fold higher activity compared to free tyrosine. Comparison of Y-rich sequence consisted of 13 amino acids and its Y-to-F substitution mutant sequence revealed that the tyrosine-residues on Y-rich peptide derived from prion may contribute to the higher production of O2 •-. These data suggest that the tyrosine residues on prion molecules could be additional targets of the prion-mediated reactions through intra-or inter-molecular interactions. Lastly, possible mechanism of O2 •-generation and the impacts of such self-redox events on the conformational changes in prion are discussed.
It is widely accepted that plant peroxidases (EC1.11.1.7) can catalyze the generation of superoxide anion upon oxidation of substrates in the presence of hydrogen peroxide. Similarly, recent studies have shown that peptides derived from human prion protein (PrP) catalyses the generation of superoxide coupled to oxidation of neurotransmitters and their analogues. As human PrP possesses four putative copper-binding regions, the binding to copper confers the catalytic activities to PrP and derived peptides. Recent demonstrations suggested that PrP-derived copper-binding peptides catalyze the generation of superoxide in peroxidative manner involving hydrogen peroxide as electron acceptor and aromatic compounds or phenolics as electron donors. The least components required for the reaction were shown to be (i) short peptides with copper-binding capability, (ii) copper ions, (iii) hydrogen peroxide, and (iv) amines or phenolics. Notably, tyrosine residue(s) on PrP itself can be a good phenolic substrate, thus the superoxide generating reaction could be completed within copper-bound PrP supplied with hydrogen peroxide. According to earlier studies, at least single histidine (His or H) residue is required for binding of copper, and the catalytically active copper-binding motif within PrP-derived peptides was determined to be X-X-H (where X can be any amino acids followed by His). This review covers the latest results performing and explaining the mechanism of catalytic activities found in copper-bound short peptides derived from PrPs, by comparing the mechanism for the reactions catalyzed by natural plant peroxidase. Furthermore, chemical and biological approaches for designing the novel small-sized artificial enzymes mimicking the natural peroxidase are described.
Free Superoxide is an Intermediate in the Production of H2 O2 by Copper(I)-Aβ Peptide and O2
Angewandte Chemie (International ed. in English), 2015
Oxidative stress is considered as an important factor and an early event in the etiology of Alzheimer's disease (AD). Cu bound to the peptide amyloid-β (Aβ) is found in AD brains, and Cu-Aβ could contribute to this oxidative stress, as it is able to produce in vitro H2 O2 and HO(.) in the presence of oxygen and biological reducing agents such as ascorbate. The mechanism of Cu-Aβ-catalyzed H2 O2 production is however not known, although it was proposed that H2 O2 is directly formed from O2 via a 2-electron process. Here, we implement an electrochemical setup and use the specificity of superoxide dismutase-1 (SOD1) to show, for the first time, that H2 O2 production by Cu-Aβ in the presence of ascorbate occurs mainly via a free O2 (.-) intermediate. This finding radically changes the view on the catalytic mechanism of H2 O2 production by Cu-Aβ, and opens the possibility that Cu-Aβ-catalyzed O2 (.-) contributes to oxidative stress in AD, and hence may be of interest.
Ozone-inducible (OI ) peptides found in plants contain repeated sequences consisting of a hexa-repeat unit (YGH GGG) repeated 8–10 times in tandem, and each unit tightly binds copper. To date, the biochemical roles for OI peptides are not fully understood. Here, we demonstrated that the hexa-repeat unit from OI peptides behaves as metal-binding motif catalytically active in the superoxide generation. Lastly, possible mechanisms of the reaction and biological consequence of the reactions are discussed by analogy to the action of human prion octarepeat peptides.