Dynamics of supramolecular biological systems by synchrotron radiation

Wakabayshi等人基于肌动蛋白单体的结晶学数据，构建了F-肌动蛋白与原肌球蛋白结合的模型，该模型表明，松弛状态下细丝的X射线强度计算值与实测值吻合良好。由此可见，肌动蛋白分子的结构变化在肌肉收缩中起着重要作用。Wakabayashi等人用电子冷冻显微镜成功地观察到了相互作用的放线肌球蛋白头部复合体，分辨率为2 nm。显微照片表明，肌动蛋白和肌球蛋白分子之间的相对取向不是恒定的，在滑动运动中存在着不同的相互作用部位。此外，Katayama等人还可以使用快速冷冻、冷冻断裂和深度蚀刻技术在添加ATP后获得云母表面肌动蛋白-肌球蛋白复合体的图像。结果表明，肌球蛋白头部结合在肌动蛋白细丝上具有较宽的取向分布，可以在多种肌动蛋白单体的范围内移动。Namba等人用电子冷冻显微镜和X射线纤维衍射法研究了鞭毛细丝多态的分子机制。结果表明，纤丝核心的双管状结构对于鞭毛的多态能力是必不可少的，而鞭毛的多态能力是细菌趋向性游动调节所必需的。Tokunaga等人用X射线衍射法研究了细菌视紫红质D96N突变体的结构，其中间体的寿命比天然突变体长，并检测到光周期中M和N中间体的结构发生了显著变化。Tawada等人展示了通过化学交联的肌球蛋白-肌动蛋白交叉桥产生的力量，以响应镁ATP的耗尽。他们还研究了动蛋白在微管平移滑动运动中的波动，并表明蛋白质摩擦对滑动运动的可能机制产生了显着的限制。

Wakabayshi et al.constructed the model of F-actin bound with tropomyosin which showed the good fitness between the calculated and observed x-ray intensities from the thin filament in relaxing state, based on the crystallographic data of actin monomers. From this result, it was suggested that the structural change of the actin molecule playd important role in the contraction of muscle. Wakabayashi et al.observed successfuly the interacting actinmyosin head complex at 2 nm resolution by electron cryo-microscopy. The micrographs indicated that the relative orientation between actin and myosin molecules was not constant and the various interaction sites existed in the sliding movement. Also, Katayama et al.could obtain images of the actin-heavy meromyosin complexes on mica surfaces after the addition of ATP using a quick-freeze, freeze-fracture, deep-etch technique. The result showed that the myosin head bound to the actin filament with a broad orientational distribution and could move over the range of several actin monomers. Namba et al.studied the molecular mechanism of polymorphism of flagellar filaments by electron cryo-microscopy and x-ray fiber diffraction method. It appeared that the double tublar structure of the filament core was essential for the polymorphic ability of flagellar filaments, which is required for the swimming-tunbling of bacterial taxies. Tokunaga et al.studied the structure of the D96N mutant of bacteriorhodopsin, the intermediates of which had longer life times than the native ones, by x-ray diffraction and detected significant changes of the structure at M and N intermediates of the photocycle. Tawada et al.showed the force production by chemically crosslinked myosin-actin cross-brideges in response to MgATP depletion. They also studied the fluctuation in the translational sliding movement of microtubles by kinesin and showed that the protein friction places significant constraint on the possible mechanisms of the sliding movement.