Glucagon Fibril Polymorphism Reflects Differences in Protofilament Backbone Structure
Glucagon Fibril Polymorphism Reflects Differences in Protofilament Backbone Structure
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DOI：
10.1016/j.jmb.2010.02.012
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发表时间：
2010-04-09
影响因子：
5.6
通讯作者：
Otzen, Daniel Erik
中科院分区：
文献类型：
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作者：
Andersen, Christian Beyschau;Hicks, Matthew R.;Otzen, Daniel Erik
当通过透射电子显微镜观察时，由29个残基的肽激素胰高血糖素在不同浓度下形成的淀粉样原纤维具有显著不同的形态。在低浓度（0.25 mg/mL）下形成的原纤维由两个或多个具有规则扭曲的原丝组成，而在高浓度（8 mg/mL）下形成的原纤维由两个直的原丝组成。在这里，我们探讨胰高血糖素多态性的结构差异，使用蛋白水解降解，线性和圆二色性，傅里叶变换红外光谱（FTIR），和X-射线纤维衍射。形态学差异在所有结构水平上都是永久存在的，这表明两种原纤维类别在原丝骨架区域、二级结构、发色团沿原纤维轴沿着排列和原纤维超结构方面不同。直原纤维显示出传统的β-片层丰富的远紫外圆二色性光谱，而扭曲的原纤维主要由β-转角的贡献。傅里叶变换红外光谱证实了这一点，也表明了一个更密集的骨干与较弱的氢键扭曲的形态。根据线性二色性，直原纤维中的二级结构元件和芳香族侧链相对于排列轴比扭曲原纤维更高度有序。直纤丝衍射图中的一系列高周期性反射可以拟合到预期的圆柱体衍射图案。因此，直原纤维中的高度整合的结构组织导致具有明确限定的边缘的紧凑且高度均匀的原纤维。长时间的蛋白水解消化证实，直原纤维非常致密和稳定，而扭曲的原纤维骨架的部分更容易降解。两种形态的消化模式的差异与来自两种算法的预测相关，表明多态性是胰高血糖素序列中固有的。胰高血糖素提供了一个引人注目的例子，说明相同的短序列如何折叠成两种显着不同的纤维结构。(C)2010爱思唯尔有限公司保留所有权利。
Amyloid fibrils formed by the 29-residue peptide hormone glucagon at different concentrations have strikingly different morphologies when observed by transmission electron microscopy. Fibrils formed at low concentration (0.25 mg/mL) consist of two or more protofilaments with a regular twist, while fibrils at high concentration (8 mg/mL) consist of two straight protofilaments. Here, we explore the structural differences underlying glucagon polymorphism using proteolytic degradation, linear and circular dichroism, Fourier transform infrared spectroscopy (FTIR), and X-ray fiber diffraction. Morphological differences are perpetuated at all structural levels, indicating that the two fibril classes differ in terms of protofilament backbone regions, secondary structure, chromophore alignment along the fibril axis, and fibril superstructure. Straight fibrils show a conventional beta-sheet-rich far-UV circular dichroism spectrum whereas that of twisted fibrils is dominated by contributions from beta-turns. Fourier transform infrared spectroscopy confirms this and also indicates a more dense backbone with weaker hydrogen bonding for the twisted morphology. According to linear dichroism, the secondary structural elements and the aromatic side chains in the straight fibrils are more highly ordered with respect to the alignment axis than the twisted fibrils. A series of highly periodical reflections in the diffractogram of the straight fibrils can be fitted to the diffraction pattern expected from a cylinder. Thus, the highly integrated structural organization in the straight fibril leads to a compact and highly uniform fibril with a well-defined edge. Prolonged proteolytic digestion confirmed that the straight fibrils are very compact and stable, while parts of the twisted fibril backbone are much more readily degraded. Differences in the digest patterns of the two morphologies correlate with predictions from two algorithms, suggesting that the polymorphism is inherent in the glucagon sequence. Glucagon provides a striking illustration of how the same short sequence can be folded into two remarkably different fibrillar structures. (C) 2010 Elsevier Ltd. All rights reserved.