X-RAY STRUCTURAL ANALYSES OF THIN FILAMENTS IN A SKELETAL MUSCLE DURING CONTRACTION AND MYOSIN HEADS DURING AN HYDROLYSIS OF ATP

青蛙骨骼肌收缩时细丝的结构变化首先，我们利用同步辐射精确测量了等距收缩肌肉x射线衍射图中肌动蛋白丝基反射的间距变化。我们发现在肌动蛋白丝和肌凝蛋白丝中有0.2-0.3%的延伸。这种长丝的延展性是有弹性的。这些结果为肌肉中的力产生机制提供了一个很好的见解。其次，我们测量了薄长丝基层线高达-13A的强度。利用肌动蛋白单体和原肌球蛋白的原子数据，我们构建了细丝的模型，并计算了差分傅里叶，表明细丝内部发生了结构变化。模型研究显示，肌动蛋白与肌凝蛋白头的相互作用引起了丝内肌动蛋白结构域的明显变化。原肌凝蛋白分子也在方位角方向上移动了约55a，比先前肌肉调节的空间阻滞假说所假设的要小同步加速器x射线溶液散射显示，肌凝蛋白头部在ATP水解过程中改变了构象：旋转半径和最大弦长分别减少了3A和10A。利用原子数据进行的模型研究表明，轻链结合结构域在包括长轴在内的平面上围绕氨基酸711旋转了12个，向下旋转了10个。从核苷酸类似物的实验来看，ADP发生了构象变化。P_i状态，并在产品发布步骤中反转。我们成功地制备了非聚合的肌动蛋白-肌球蛋白头复合物，并通过x射线溶液散射研究了该复合物的溶液结构。结果表明，肌动蛋白单体结合在肌凝蛋白头催化结构域的近端，中心到中心距离为75A。这些研究为肌动球蛋白系统中最小能量转导单元的结构研究开辟了一条非常重要的途径。少

[1] Structural change of the thin filaments during contraction of frog skeletal muscleFirstly, we measured precisely the spacing changes of the actin filament-based reflections in the X-ray diffraction pattern from an isometrically contracting muscle using synchrotron radiation. We found 0.2-0.3% of extnsion in the actin filaments as well as the myosin filaments. Such filament extensibility was elastic. These results provided a great insight to a force-generation mechanism in muscle. Secondly, we measured intensities of the thin filament-based layr lines up to -13A.Using the atomic data of the actin monomer and tropomyosin, we constructed a model of the thin filament and calculated a difference Fourier, indicating that the structural change occurred within the thin filaments. Modeling studies revealed distinct changes of the domain structure of actin in the filament which were induced by interaction with myosin heads. Tropomyosin molecules also moved in the azimuthal direction by about … More 5A,less than previously postulated in a steric block hypothesis of muscle regulation.[2] Conformational changes of the myosin head and the solution structure of an actomyosin complexSynchrotron X-ray solution scattering revealed that the myosin head altered its conformation during an hydrolysis of ATP : the radius of gyration and maximum chord length decreased by 3A and 10A,respectively. Modeling studies using the atomic data indicated that the light chain-binding domain rotated around the amino acid 711 by 12ﾟ downward by 10ﾟ in the plane including its long axis. From the experiments with nucleotide analogs, the conformational changes occurred in the ADP.P_i state and reversed in the product release steps. We succeeded in preparing non-polymerized actin-myosin head complex and investigated the solution structure of this complex by X-ray solution scattering. The result indicated that the actin monomer bound to the proximal end of the catalytic domain of the myosin head with a center-to-center distance of 75A.Such studies have opened a very important root to structural studies of the smallest energy transducing unit in the actomyosin system. Less