Amorphous Aggregation of Cytochrome c with Inherently Low Amyloidogenicity Is Characterized by the Metastability of Supersaturation and the Phase Diagram
Amorphous Aggregation of Cytochrome c with Inherently Low Amyloidogenicity Is Characterized by the Metastability of Supersaturation and the Phase Diagram
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DOI：
10.1021/acs.langmuir.5b03810
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发表时间：
2016-03-01
期刊：
影响因子：
3.9
通讯作者：
Lee, Young-Ho
中科院分区：
文献类型：
--
作者：
Lin, Yuxi;Kardos, Jozsef;Lee, Young-Ho
尽管对细胞色素c的折叠和功能进行了广泛的研究，但其聚集的机制在很大程度上仍然未知。我们在此研究了生理上相关的两种类型的细胞色素c的聚集行为，金属结合的细胞色素c，以及在酒精/水混合物中预测的具有高淀粉样变性的片段。虽然由于溶解度高，全息细胞色素c的聚集倾向较低，但明显展开的载脂蛋白细胞色素c缺乏血红素假基，强烈促进了无定形聚集倾向，并增加了疏水性。银结合的载脂蛋白细胞色素c增加了纤维聚集（即原纤维或未成熟原纤维）的能力，这是由于载脂蛋白细胞色素c在银的强结合下发生了微妙的结构变化。然而，成熟的淀粉样蛋白原纤维未检测到任何细胞色素c变异或其片段，即使是广泛的超声检查，这是一种强大的淀粉样蛋白诱导剂。这些结果揭示了细胞色素c内在的低淀粉样蛋白原性，这有利于其内稳态和功能，促进折叠和减少不可逆淀粉样蛋白的形成。我们认为细胞色素c的低淀粉样变性本质上是由于过饱和度的低亚稳态。基于溶解度和聚集类型构建的相图有助于对蛋白质聚集的全面理解。此外，无定形聚集（也被视为蛋白质的一般性质）和淀粉样蛋白颤动可以通过过饱和亚稳性相互区分。
Despite extensive studies on the folding and function of cytochrome c, the mechanisms underlying its aggregation remain largely unknown. We herein examined the aggregation behavior of the physiologically relevant two types of cytochrome c, metal-bound cytochrome c, and its fragment with high amyloidogenicity as predicted in alcohol/water mixtures. Although the aggregation propensity of holo cytochrome c was low due to high solubility, markedly unfolded apo cytochrome c, lacking the heme prosthetic group, strongly promoted the propensity for amorphous aggregation with increases in hydrophobicity. Silver-bound apo cytochrome c increased the capacity of fibrillar aggregation (i.e., protofibrils or immature fibrils) due to subtle structural changes of apo cytochrome c by strong binding of silver. However, mature amyloid fibrils were not detected for any of the cytochrome c variants or its fragment, even with extensive ultrasonication, which is a powerful amyloid inducer. These results revealed the intrinsically low amyloidogenicity of cytochrome c, which is beneficial for its homeostasis and function by facilitating the folding and minimizing irreversible amyloid formation. We propose that intrinsically low amyloidogenicity of cytochrome c is attributed to the low metastability of supersaturation. The phase diagram constructed based on solubility and aggregate type is useful for a comprehensive understanding of protein aggregation. Furthermore, amorphous aggregation, which is also viewed as a generic property of proteins, and amyloid fibrillation can be distinguished from each other by the metastability of supersaturation.