Yagi N, Ohta N, Iida T, Inoue K
Japan Synchrotron Radiation Research Institute, SPring-8, Kouto, Sayo, Hyogo 679-5198, Japan.
J Mol Biol. 2006 Sep 15;362(2):327-33. doi: 10.1016/j.jmb.2006.07.041. Epub 2006 Jul 27.
The peptide hormone insulin forms a spherical aggregate, called a spherulite, at low pH and high temperature. A spherulite is composed of a core and many fibrils extending from it. These fibrils are thought to be amyloid fibers with a beta-sheet structure. In the present study, spherulites with a diameter of 50-100 microm were examined by X-ray fiber diffraction using a 6 microm beam. When a spherulite was scanned with the microbeam and the observed diffraction patterns were arranged in a two-dimensional array, the direction of the scatter was centrosymmetric, demonstrating a symmetric growth of fibrils. There were diffraction peaks at Bragg spacings of 23 nm, 3.3 nm and 1.2 nm in the direction perpendicular to the fibrils and 0.48 nm along the fibrils. The 0.48 nm reflection shows that the hydrogen bonds between beta-strands are along the fibril. The 23 nm reflection corresponds to the separation between fibrils, the 3.3 nm reflection is due to the arrangement of protofilaments, and the 1.2 nm reflection arises from the arrangement of peptide chains. On the basis of these results, a model of a fibril with an extended insulin molecule is proposed.
肽激素胰岛素在低pH值和高温下会形成一种球形聚集体，称为球晶。球晶由一个核心和许多从其延伸出的纤维组成。这些纤维被认为是具有β-折叠结构的淀粉样纤维。在本研究中，使用6微米的光束通过X射线纤维衍射对直径为50 - 100微米的球晶进行了检测。当用微光束扫描球晶并将观察到的衍射图案排列成二维阵列时，散射方向是中心对称的，这表明纤维呈对称生长。在垂直于纤维的方向上，布拉格间距为23纳米、3.3纳米和1.2纳米处有衍射峰，沿纤维方向有0.48纳米的衍射峰。0.48纳米的反射表明β-链之间的氢键沿纤维方向排列。23纳米的反射对应于纤维之间的间距，3.3纳米的反射是由于原纤维的排列，1.2纳米的反射源于肽链的排列。基于这些结果，提出了一个具有伸展胰岛素分子的纤维模型。
