Cosolvent effects on the fibrillation reaction of human IAPP.
Cosolvent effects on the fibrillation reaction of human IAPP.
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DOI：
10.1039/c3cp44412k
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发表时间：
2013-05
期刊：
影响因子：
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通讯作者：
J. Seeliger;K. Estel;Nelli Erwin;R. Winter
中科院分区：
文献类型：
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作者：
J. Seeliger;K. Estel;Nelli Erwin;R. Winter
由于细胞环境中存在各种类型的渗透物，本研究主要关注稳定（TMAO和甜菜碱）和不稳定（尿素）共溶剂对高度淀粉样蛋白生成的胰岛淀粉样多肽（IAPP）聚集和纤颤反应的影响。IAPP与2型糖尿病相关，是伴随β细胞膜通透和最终β细胞丢失的疾病的原因。为了揭示共溶剂对IAPP纤颤的聚集动力学、构象和形态变化的影响，应用了硫黄酮T荧光光谱、原子力显微镜和衰减全反射傅立叶变换红外光谱。对于氧化三甲胺（TMAO），观察到原纤维生长速率降低，而滞后期基本保持不变，这表明相容溶质能够稳定大的低聚物和原纤维结构，从而阻碍原纤维的伸长，甜菜碱则不那么明显。相反，尿素表现出浓度依赖的滞后期延长，表明IAPP在其未折叠的单体状态下稳定，从而导致IAPP核形成迟缓。尿素与氧化三甲胺的混合物，以及在较小程度上与甜菜碱的混合物，表现出反作用。TMAO能够充分补偿尿素引起的延迟期延长。这与TMAO和尿素在蛋白质折叠和展开实验中的反作用的发现非常吻合。数据还表明，这些共溶剂的影响仅对聚集动力学有影响，而不会显著改变最终的IAPP纤维形态，即溶液结构和共溶剂组成本质上只影响纤颤过程的动力学。
Owing to the presence of various types of osmolytes in the cellular environment, this study focuses on the impact of stabilizing (TMAO and betaine) as well as destabilizing (urea) cosolvents on the aggregation and fibrillation reaction of the highly amyloidogenic islet amyloid polypeptide (IAPP). IAPP is associated with type-2 diabetes mellitus and is responsible for the disease accompanying β-cell membrane permeabilization and final β-cell loss. To reveal the impact of the cosolvents on the aggregation kinetics, conformational and morphological changes upon IAPP fibrillation, Thioflavin T fluorescence spectroscopy, atomic force microscopy and attenuated total reflection Fourier-transform infrared spectroscopy were applied. For TMAO, and less pronounced for betaine, a decrease of the growth rate of fibrils is observed, whereas the lag phase remains essentially unchanged, indicating the ability of the compatible solutes to stabilize large oligomeric and protofibrillar structures and therefore hamper fibril elongation. Conversely, urea displays concentration-dependent prolongation of the lag phase, indicating stabilization of IAPP in its unfolded monomeric state, hence leading to retardation of IAPP nuclei formation. Mixtures of urea with TMAO, and to a lesser extent with betaine, exhibit a counteractive effect. TMAO is able to fully compensate the prolonged lag phase induced by urea. This strongly matches the findings of a counteraction of TMAO and urea in protein folding and unfolding experiments. The data also reveal that the influence of these cosolvents is only on the aggregation kinetics without markedly changing the final IAPP fibrillar morphology, i.e., the solution structure and cosolvent composition essentially affect the kinetics of the fibrillation process only.