Alzheimer's disease related copper(II)-β-amyloid peptide exhibits phenol monooxygenase and catechol oxidase activities
Alzheimer's disease related copper(II)-β-amyloid peptide exhibits phenol monooxygenase and catechol oxidase activities
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DOI：
10.1002/anie.200501013
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发表时间：
2005-01-01
影响因子：
16.6
通讯作者：
Ming, LJ
中科院分区：
文献类型：
--
作者：
da Silva, GFZ;Ming, LJ
在过去的几年里，大量的研究工作都集中在金属依赖性机制的研究上，这些机制导致了阿尔茨海默病（AD）的神经病理学改变。[1]自组装的金属-β-淀粉样蛋白（Aβ）肽原纤维是这种疾病的标志[2]，并已归因于在还原条件下以FeIII和CuII为中心的H2 O2生成。后者，H2 O2，已被假定为是显着的重要性与AD中的神经病变。[3，4]然而，除了受到普遍好评的ROS（活性氧物质;如H2 O2）攻击外，与AD神经病理学相关的详细化学过程一直是一个被忽视的领域。[5]因此，更好地了解以金属为中心的氧化还原化学和ROS的产生机制及其命运可以为预防和治疗AD提供潜在的策略。已知生物系统中的氧化还原化学的几个例子与双核或多核“3型”Cu氧化酶有关，[6]这可能与CuIIAβ的氧化还原活性有关。[1-4]已经成功地证明了靶向3型铜中心的许多化学模型系统含有高活性的等电子铜-二氧物质（即CuII 2-μ-η1：η1-过氧、CuII 2-μ-η2：η2-过氧和CuIII 2-双-μ-氧），其负责铜依赖性氧化和羟基化反应。[6-9]尽管进行了广泛的建模研究，但这些酶的肽模拟物显然已被排除在研究之外。CuIIAβ似乎填补了这一差距，因为它是一种天然存在的Cu-肽复合物，显示出与氧相关的氧化还原化学[1-4]，尽管缺乏有关其氧结合和活化机制的详细信息。在这里，我们提出的结果，汇集了两个不同的研究领域：阿尔茨海默病和3型铜中心。结果表明，Cu Ⅱ络合物（CuAβ1-20）Aβ二十碳肽金属结合结构域（DAEFR 5 HDSGY 10 EVHHN 15-KLVFF 20）具有金属中心的氧化还原化学，与3型铜酶，即苯酚单加氧酶（如酪氨酸酶）和儿茶酚氧化酶的机制一致。[10邻苯二酚在有氧条件下的氧化在低mm浓度下达到平台，并且饱和曲线很好地符合预平衡动力学[Eqs. (1)和（2）][12]得到速率常数kcat= 0.154 s·h ~（-1），解离常数K ′ app = 0.35 mm（图1a），和一个显著的二级速率常数kcat/K ′ app = 440 m·h ~（-1）s·h ~（-1）（cat=催化的，app=表观的）。由于从儿茶酚形成醌是一个双电子氧化过程，该反应预计遵循儿茶酚氧化酶的双电子双核反应途径，[13]其中儿茶酚与活性位点二铜（ii）中心的结合导致中心还原产生二铜（i），同时产生邻醌。还原的二铜（i）中心可以结合分子氧以提供活性过氧桥连的二铜（ii）中心，其可以进一步氧化随后结合的底物。H2 O2也可以在该反应途径中在还原剂如底物本身的存在下从过氧桥连的二铜（ii）中心产生。这种在还原条件下产生H2 O2的途径与AD研究中的先前观察结果一致。[3]在几种化学模型系统的动力学研究中[14]和在多酚的氧化中也观察到了儿茶酚氧化酶样机制。
Over the past few years an enormous effort has been directed toward the investigation of the metal-dependent mechanisms that lead to the neuropathology of Alzheimer s disease (AD).[1] The self-assembled metallo-β-amyloid (Aβ) peptide fibrils are the hallmark of this disease [2] and have been attributed to FeIII-and CuII-centered generation of H2O2 under reducing conditions. The latter, H2O2, has been postulated to be of significant importance in connection with neuropathy in AD.[3, 4] However, an area of oversight has been the detailed chemical processes associated with the neuropathology of AD, besides the generally acclaimed assault by ROS (reactive oxygen species; eg H2O2).[5] Hence, a better understanding of metal-centered redox chemistry and the mechanism for the generation of ROS and their fate can provide insight into potential strategies for the prevention and treatment of AD. Several examples of redox chemistry in biological systems are known to be associated with di-or multinuclear “Type-3” Cu oxidases,[6] which may be related to the redox activity of CuIIAβ.[1–4] A number of chemical model systems that target Type-3 copper centers have successfully been demonstrated to contain highly active isoelectronic copper–dioxygen species (ie CuII2-μ-η1: η1-peroxo, CuII 2-μ-η2: η2-peroxo, and CuIII 2-bis-μ-oxo), which are responsible for copper-dependent oxidation and hydroxylation reactions.[6–9] Despite extensive modeling studies, peptide mimics of these enzymes have apparently been excluded from the studies. CuIIAβ seems to fill the gap as it is a naturally occurring Cu–peptide complex demonstrated to exhibit oxygen-associated redox chemistry,[1–4] although details about its oxygen binding and activation mechanisms are lacking. Herein, we present results which bring together two distinct fields of research: Alzheimer s disease and Type-3 copper centers. The results elucidate that the CuII complex (CuAβ1–20) of the icosapeptidyl metalbinding domain of Aβ (DAEFR5HDSGY10EVHHN15-KLVFF20) exhibits metal-centered redox chemistry that is consistent with the mechanisms of the Type-3 copper enzymes, namely, phenol monooxygenase (eg tyrosinase) and catechol oxidase.The metal-centered redox chemistry of CuAβ1–20 was probed using catechol and the more-inert phenol as substrates.[10, 11] The oxidation of catechol under aerobic conditions reached a plateau at low mm concentrations, and the saturation profile fits well to pre-equilibrium kinetics [Eqs.(1) and (2)][12] to afford the rate constant kcat= 0.154 sÀ1, the dissociation constant K’app= 0.35 mm (Figure1a), and a significant second-order rate constant kcat/K’app= 440mÀ1 sÀ1 (cat= catalytic, app= apparent). As the formation of quinone from catechol is a two-electron oxidative process, the reaction is expected to follow the two-electron dinuclear reaction pathway for catechol oxidase,[13] wherein the binding of catechol to the active-site dicopper (ii) center results in the reduction of the center to yield dicopper (i) with concomitant production of o-quinone. The reduced dicopper (i) center can bind dioxygen to afford the active peroxo-bridged dicopper (ii) center, which can further oxidize a subsequently bound substrate. H2O2 can also be generated in this reaction pathway from the peroxobridged dicopper (ii) center in the presence of a reducing agent such as the substrate itself. This pathway for the production of H2O2 under reducing conditions is consistent with previous observations in AD studies.[3] The catechol oxidase like mechanism has also been observed in kinetic studies of several chemical model systems [14] and in the oxidation of polyphenols by …