Restoration of 3-D structure of insect flight muscle from a rotationally averaged 2-D X-ray diffraction pattern

Hiroyuki Iwamoto
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Abstract

The contractile machinery of muscle, especially that of skeletal muscle, has a very regular array of contractile protein filaments, and gives rise to a very complex and informative diffraction pattern when irradiated with X-rays. However, the analysis of the diffraction patterns is often difficult, because (1) only rotationally averaged diffraction patterns can be obtained, resulting in substantial loss of information, and (2) the contractile machinery contains two different sets of protein filaments (actin and myosin) with different helical symmetries, and the reflections originating from them are often overlapped. These problems may be solved if the real-space 3-D structure of the contractile machinery is directly calculated from the diffraction pattern. Here we demonstrate that, by using the conventional phase-retrieval algorithm (hybrid input-output), the real-space 3-D structure of the contractile machinery can be well restored from a single rotationally averaged 2-D diffraction pattern. In this calculation, we used a model structure of insect flight muscle, known to have a very regular structure. Possibilities of extending this technique to the actual muscle diffraction patterns is discussed.
从旋转平均二维 X 射线衍射图样还原昆虫飞行肌肉的三维结构
肌肉(尤其是骨骼肌)的收缩机制具有非常规则的收缩蛋白丝阵列,用 X 射线照射时会产生非常复杂且信息丰富的衍射图样。然而,对衍射图样的分析往往很困难,因为:(1)只能获得旋转平均衍射图样,导致大量信息丢失;(2)收缩机械包含两组不同螺旋对称性的不同蛋白丝(肌动蛋白和肌球蛋白),它们产生的反射常常重叠。如果能根据衍射图样直接计算出收缩机械的实空间三维结构,这些问题就能迎刃而解。在这里,我们证明了通过使用传统的相位检索算法(混合输入输出),可以从单一的旋转平均二维衍射图样中很好地还原出收缩机械的实空间三维结构。在计算中,我们使用了昆虫飞行肌肉的模型结构,已知其结构非常规则。我们还讨论了将这一技术扩展到实际肌肉衍射图样的可能性。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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