A two-site mechanism for the inhibition of IAPP amyloidogenesis by zinc.
A two-site mechanism for the inhibition of IAPP amyloidogenesis by zinc.
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DOI：
10.1016/j.jmb.2011.05.015
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发表时间：
2011-07-08
影响因子：
5.6
通讯作者：
Ramamoorthy A
中科院分区：
文献类型：
--
作者：
Salamekh S;Brender JR;Hyung SJ;Nanga RP;Vivekanandan S;Ruotolo BT;Ramamoorthy A
人胰岛淀粉样多肽（humanisletamyloidpolypeptide，hIAPP）是一种高淀粉样蛋白，在葡萄糖浓度升高时与胰岛素共同分泌。胰岛细胞附近hIAPP淀粉样斑块的形成与人类胰岛素分泌β细胞的死亡和II型糖尿病的进展有关。由于健康个体和II型糖尿病患者都产生和分泌hIAPP，因此寻找与储存hIAPP和预防淀粉样变性有关的因素是合理的。我们以前已经表明，锌抑制hIAPP的不溶性淀粉样蛋白斑块的形成，但是，在潜在的机制仍然存在显着的模糊性。在这项研究中，我们表明锌以与细胞外环境中发现的浓度相似的微摩尔浓度与未聚集的hIAPP结合。相比之下，hIAPP的纤维状淀粉样蛋白形式对锌具有低亲和力。从ITC实验获得的结合化学计量表明锌有利于hIAPP六聚体的形成。结合锌的hIAPP的高分辨率NMR结构揭示了电子环境沿着残基的变化，所述残基将位于两亲性hIAPP α-螺旋的沿着一面，所述两亲性hIAPP α-螺旋被提出作为淀粉样蛋白形成的中间体。ESI-MS研究的结果表明，单一锌主要结合hIAPP，并揭示锌抑制二聚体的形成。在较高浓度的锌下，第二个锌与hIAPP结合，表明存在低亲和力的二级结合位点。结合起来，这些结果表明锌促进低聚物的形成，同时为淀粉样纤维的形成创造一个充满活力的障碍。
Human Islet Amyloid Polypeptide (hIAPP) is a highly amyloidogenic protein cosecreted with insulin in response to glucose levels. The formation of hIAPP amyloid plaques near islet cells has been linked to the death of insulin-secreting beta-cells in humans and the progression of type II diabetes. Since both healthy individuals and those with type II diabetes produce and secrete hIAPP, it is reasonable to look for factors involved in storing hIAPP and preventing amyloidosis. We have previously shown that zinc inhibits the formation of insoluble amyloid plaques of hIAPP; however, there remains significant ambiguity in the underlying mechanisms. In this study, we show zinc binds unaggregated hIAPP at micromolar concentrations similar to those found in the extracellular environment. By contrast, the fibrillar amyloid form of hIAPP has low affinity for zinc. The binding stoichiometry obtained from ITC experiments indicates zinc favors the formation of hIAPP hexamers. High-resolution NMR structures of hIAPP bound to zinc reveal changes in the electron environment along residues that would be located along one face of the amphipathic hIAPP alpha-helix proposed as an intermediate for amyloid formation. Results from ESI-MS investigations showed that a single zinc is predominantly bound to hIAPP and revealed that zinc inhibits the formation of the dimer. At higher concentrations of zinc a second zinc binds to hIAPP, suggesting the presence of a low affinity secondary binding site. Combined, these results suggest zinc promotes the formation of oligomers while creating a energetic barrier for the formation of amyloid fibers.
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