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

[1]青蛙骨骼肌收缩过程中细丝结构的变化首先，我们利用同步辐射技术精确测量了等长收缩肌肉X射线衍射图中肌动蛋白折射率的间距变化。我们发现肌动蛋白丝和肌球蛋白丝中有0.2-0.3%的延伸。这种长丝延展性是弹性的。这些结果提供了一个很大的洞察力在肌肉中的力产生机制。其次，我们测量了-13 A以下的细丝结构线的强度，利用肌动蛋白单体和原肌球蛋白的原子数据，建立了细丝结构模型，并计算了其傅立叶差，表明结构变化发生在细丝内部。建模研究揭示了与肌球蛋白头相互作用引起的肌动蛋白在细丝中的结构域的明显变化。原肌球蛋白分子也在方位角方向上移动了约 关于我们 5A，小于先前在肌肉调节的空间阻滞假说中所假设的。[2]肌球蛋白头部构象变化及肌动球蛋白复合物的溶液结构同步辐射X射线溶液散射研究表明，在ATP水解过程中，肌球蛋白头部的构象发生了变化，回转半径和最大弦长分别减小了3A和10A.使用原子数据的建模研究表明，轻链结合结构域在包括其长轴的平面内围绕氨基酸711向下旋转12 π/10 π。从核苷酸类似物的实验中，构象变化发生在ADP.P_i状态，并在产物释放步骤中逆转。成功地制备了非聚合肌动蛋白-肌球蛋白头复合物，并用X-射线溶液散射研究了该复合物的溶液结构。结果表明，肌动蛋白单体以75 A的中心距与肌球蛋白头的催化结构域近端结合，为肌动球蛋白系统中最小能量传递单元的结构研究奠定了基础。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