Dynamics of supramolecular biological systems by synchrotron radiation

Wakabayshi等人基于肌动蛋白单体的晶体学数据构建了F-肌动蛋白与原肌球蛋白结合的模型，该模型显示了来自松弛状态的细丝的计算的X射线强度与观察的X射线强度之间的良好拟合。这一结果提示肌动蛋白分子结构的变化在肌肉收缩中起重要作用。Wakabayashi等用冷冻电子显微镜成功地观察到2nm分辨率的相互作用的肌动蛋白头复合物。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各种相互作用位点。此外，Katayama等人使用快速冷冻、冷冻断裂、深蚀刻技术，在加入ATP后，可以获得云母表面上肌动蛋白-重酶解肌球蛋白复合物的图像。结果表明，肌球蛋白头与肌动蛋白丝结合，具有较宽的取向分布，可在几个肌动蛋白单体的范围内运动。Namba等用冷冻电镜和x-射线纤维衍射方法研究了鞭毛丝多态性的分子机制。这表明鞭毛核心的双管结构是鞭毛的多态性所必需的，而鞭毛的多态性是细菌游动的必要条件。Tokunaga等人通过X射线衍射研究了细菌视紫红质的D96 N突变体的结构，其中间体比天然的中间体具有更长的寿命，并检测到光循环的M和N中间体的结构的显著变化。Tawada等表明，化学交联的肌球蛋白-肌动蛋白交叉桥接物响应MgATP消耗而产生力。他们还研究了驱动蛋白引起的微管平移滑动运动的波动，并表明蛋白质摩擦力对滑动运动的可能机制有重要的约束。

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.