Probing the Sources of the Apparent Irreproducibility of Amyloid Formation: Drastic Changes in Kinetics and a Switch in Mechanism Due to Micelle like Oligomer Formation at Critical Concentrations of IAPP
Probing the Sources of the Apparent Irreproducibility of Amyloid Formation: Drastic Changes in Kinetics and a Switch in Mechanism Due to Micelle like Oligomer Formation at Critical Concentrations of IAPP
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DOI：
10.1021/jp511758w
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发表时间：
2015-02-19
影响因子：
3.3
通讯作者：
Ramamoorthy, Ayyalusamy
中科院分区：
文献类型：
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作者：
Brender, Jeffrey R.;Krishnamoorthy, Janarthanan;Ramamoorthy, Ayyalusamy
淀粉样蛋白的聚集因高度混乱而臭名昭著，条件的微小变化有时会导致聚集率的巨大变化。以淀粉样蛋白IAPP（胰岛淀粉样多肽蛋白，也称为amylin）为例，我们表明这种现象的部分原因可能与在特定临界浓度和温度下形成胶束状寡聚体有关。我们表明，芘荧光可以灵敏地检测 IAPP 形成的胶束状低聚物，并区分来自纤维和单体的胶束状低聚物，使芘成为少数特异于前原纤维低聚物的化学探针之一。我们进一步表明，这种类型的低聚物在低微摩尔范围的临界浓度和特定的临界温度下可逆形成。胶束样低聚物的形成对 IAPP 淀粉样蛋白的形成有多种影响。首先，随着接近临界浓度，纤维形成的动力学显着增加，但几乎与低于临界浓度的浓度无关，这表明低聚物在纤维形成中具有直接作用。其次，临界浓度与形成淀粉样蛋白的倾向密切相关：对于淀粉样蛋白生成性较低的 IAPP 变体和在酸性 pH 值下聚集大大减慢的天然 IAPP，观察到较高的临界浓度。此外，使用 DEST NMR 技术，我们表明淀粉样蛋白形成的途径随着接近临界点而切换，自相互作用主要在临界温度以下的 N 末端附近和临界温度以上的中心区域附近，从而协调了关于 IAPP 聚集起始的两种明显相互矛盾的观点。
The aggregation of amyloidogenic proteins is infamous for being highly chaotic, with small variations in conditions sometimes leading to large changes in aggregation rates. Using the amyloidogenic protein IAPP (islet amyloid polypeptide protein, also known as amylin) as an example, we show that a part of this phenomenon may be related to the formation of micellelike oligomers at specific critical concentrations and temperatures. We show that pyrene fluorescence can sensitively detect micellelike oligomer formation by IAPP and discriminate between micellelike oligomers from fibers and monomers, making pyrene one of the few chemical probes specific to a prefibrillar oligomer. We further show that oligomers of this type reversibly form at critical concentrations in the low micromolar range and at specific critical temperatures. Micellelike oligomer formation has several consequences for amyloid formation by IAPP. First, the kinetics of fiber formation increase substantially as the critical concentration is approached but are nearly independent of concentration below it, suggesting a direct role for the oligomers in fiber formation. Second, the critical concentration is strongly correlated with the propensity to form amyloid: higher critical concentrations are observed for both IAPP variants with lower amyloidogenicity and for native IAPP at acidic pH in which aggregation is greatly slowed. Furthermore, using the DEST NMR technique, we show that the pathway of amyloid formation switches as the critical point is approached, with self-interactions primarily near the N-terminus below the critical temperature and near the central region above the critical temperature, reconciling two apparently conflicting views of the initiation of IAPP aggregation.