Somatostatin: A Novel Substrate and a Modulator of Insulin-Degrading Enzyme Activity
Somatostatin: A Novel Substrate and a Modulator of Insulin-Degrading Enzyme Activity
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DOI：
10.1016/j.jmb.2008.11.025
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发表时间：
2009-02-06
影响因子：
5.6
通讯作者：
Coletta, Massimo
中科院分区：
文献类型：
--
作者：
Ciaccio, Chiara;Tundo, Grazia R.;Coletta, Massimo
胰岛素降解酶（IDE）是阿尔茨海默病（AD）的一个有趣的药理学靶点，因为它能水解β -淀粉样蛋白，产生非神经毒性片段。也有研究表明，生长抑素水平降低是AD的病理特征，它调节了针对β -淀粉样蛋白的neprilysin活性。在这项工作中，我们首次报道了IDE能够水解生长抑素[k(cat) (s(-1)) = 0.38 (+/-0.05)；K-m (M) = 7.5 （+/-0.9） × 10(-6)]在Phe6-Phe7氨基酸键上。另一方面，生长抑素调节IDE活性，通过降低对该底物的K-m，增强新型荧光β -淀粉样蛋白的酶切，该底物对应于a β的10-25个氨基酸序列（1-40）。圆二色光谱和表面等离子体共振成像实验表明，生长抑素与IDE结合会导致酶的二级和三级结构发生浓度依赖性的结构变化，揭示了两个可能的结合位点。高亲和力的结合位点在IDE被乙二胺四乙酸失活后消失，它与催化的Zn2+离子螯合。总的来说，这些特征表明，调节作用是由于一种变构机制：生长抑素与一个IDE亚基的活性位点结合（生长抑素被切割），诱导另一个亚基增强IDE对荧光β -淀粉样蛋白的水解活性。因此，对IDE-生长抑素相互作用的研究有助于更全面地了解IDE的功能和结构方面，以及IDE在脑内淀粉样蛋白沉积和生长抑素稳态中的病理生理意义。(C) 2008 Elsevier Ltd版权所有。
Insulin-degrading enzyme (IDE) is an interesting pharmacological target for Alzheimer's disease (AD), since it hydrolyzes beta-amyloid, producing non-neurotoxic fragments. It has also been shown that the somatostatin level reduction is a pathological feature of AD and that it regulates the neprilysin activity toward beta-amyloid.In this work, we report for the first time that IDE is able to hydrolyze somatostatin [k(cat) (s(-1)) = 0.38 (+/-0.05); K-m (M) = 7.5 (+/-0.9) x 10(-6)] at the Phe6-Phe7 amino acid bond. On the other hand, somatostatin modulates IDE activity, enhancing the enzymatic cleavage of a novel fluorogenic beta-amyloid through a decrease of the K-m toward this substrate, which corresponds to the 10-25 amino acid sequence of the A beta(1-40). Circular dichroism spectroscopy and surface plasmon resonance imaging experiments show that somatostatin binding to IDE brings about a concentration-dependent structural change of the secondary and tertiary structure(s) of the enzyme, revealing two possible binding sites. The higher affinity binding site disappears upon inactivation of IDE by ethylenediaminetetra acetic acid, which chelates, the catalytic Zn2+ ion. As a whole, these features suggest that the modulatory effect is due to an allosteric mechanism: somatostatin binding to the active site of one IDE subunit (where somatostatin is cleaved) induces an enhancement of IDE proteolytic activity toward fluorogenic beta-amyloid by another subunit. Therefore, this investigation on IDE-somatostatin interaction contributes to a more exhaustive knowledge about the functional and structural aspects of IDE and its pathophysiological implications in the amyloid deposition and somatostatin homeostasis in the brain. (C) 2008 Elsevier Ltd. All rights reserved.