Dipartimento di Scienze Chimiche, Università di Catania, Catania, Italy.
Chemistry. 2011 Feb 25;17(9):2752-62. doi: 10.1002/chem.201002809. Epub 2011 Jan 27.
Accumulation of neurotoxic amyloid-β peptide (Aβ) and alteration of metal homeostasis (metallostasis) in the brain are two main factors that have been very often associated with neurodegenerative diseases, such as Alzheimer's disease (AD). Aβ is constantly produced from the amyloidprecursor-protein APP precursor and immediately catabolized under normal conditions, whereas dysmetabolism of Aβ and/or metal ions seems to lead to a pathological deposition. Although insulin-degrading enzyme (IDE) is the main metalloprotease involved in Aβ degradation in the brain being up-regulated in some areas of AD brains, the role of IDE for the onset and development of AD is far from being understood. Moreover, the biomolecular mechanisms involved in the recognition and interaction between IDE and its substrates are still obscure. In spite of the important role of metals (such as copper, aluminum, and zinc), which has brought us to propose a "metal hypothesis of AD", a targeted study of the effect of metallostasis on IDE activity has never been carried out. In this work, we have investigated the role that various metal ions (i.e., Cu(2+), Cu(+), Zn(2+), Ag(+), and Al(3+)) play in modulating the interaction between IDE and two Aβ peptide fragments, namely Aβ(1-16) and Aβ(16-28). It was therefore possible to identify the direct effect that such metal ions have on IDE structure and enzymatic activity without interferences caused by metal-induced substrate modifications. Mass spectrometry and kinetic studies revealed that, among all the metal ions tested, only Cu(2+), Cu(+), and Ag(+) have an inhibitory effect on IDE activity. Moreover, the inhibition of copper(II) is reversed by adding zinc(II), whereas the monovalent cations affect the enzyme activity irreversibly. The molecular basis of their action on the enzyme is also discussed on the basis of computational investigations.
淀粉样β肽（Aβ）的神经毒性积累和金属内稳（metallostasis）的改变是与神经退行性疾病（如阿尔茨海默病（AD））密切相关的两个主要因素。Aβ 不断从淀粉样前体蛋白 APP 前体中产生，并在正常条件下立即被分解代谢，而 Aβ 和/或金属离子的代谢紊乱似乎导致病理性沉积。尽管胰岛素降解酶（IDE）是大脑中 Aβ 降解的主要金属蛋白酶，并且在 AD 大脑的某些区域中被上调，但 IDE 对于 AD 的发生和发展的作用还远未被理解。此外，IDE 与其底物之间的识别和相互作用所涉及的生物分子机制仍然不清楚。尽管金属（如铜、铝和锌）的重要作用使我们提出了 AD 的“金属假说”，但针对金属内稳对 IDE 活性的影响进行的靶向研究从未进行过。在这项工作中，我们研究了各种金属离子（即 Cu(2+)、Cu(+)、Zn(2+)、Ag(+)和 Al(3+)）在调节 IDE 与两种 Aβ 肽片段（即 Aβ(1-16)和 Aβ(16-28)之间相互作用中的作用。因此，有可能确定这些金属离子对 IDE 结构和酶活性的直接影响，而没有金属诱导的底物修饰引起的干扰。质谱和动力学研究表明，在所测试的所有金属离子中，只有 Cu(2+)、Cu(+)和 Ag(+)对 IDE 活性具有抑制作用。此外，锌（II）的加入可以逆转铜（II）的抑制作用，而单价阳离子则不可逆地影响酶活性。还基于计算研究讨论了它们对酶作用的分子基础。
