Motion of myosin head domains during activation and force development in skeletal muscle
Motion of myosin head domains during activation and force development in skeletal muscle
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DOI：
10.1073/pnas.1018330108
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发表时间：
2011-04-26
影响因子：
11.1
通讯作者：
Irving, Malcolm
中科院分区：
文献类型：
--
作者：
Reconditi, Massimo;Brunello, Elisabetta;Irving, Malcolm
肌肉收缩是由肌球蛋白头部区域结构的变化驱动的，肌球蛋白头部区域的结构变化是将肌动蛋白细丝拉向肌球蛋白细丝中点的“工作行程”。通过X射线干涉可以在完整的肌肉细胞中非常精确地测量肌球蛋白头部的这种运动，但到目前为止，这项技术还没有被应用于电刺激肌肉细胞后的生理激活和力的产生。通过这种方法，我们发现肌球蛋白头部结构域的长轴与静息肌肉中的细丝大致平行，它们的质心距头部结构域的C末端约7 nm。观察到的质量分布与分离的肌球蛋白细丝的电子显微照片中看到的一致，在电子显微镜下，肌球蛋白细丝的头部向后向细丝中点折叠。在电刺激后，磁头在与工作行程相反的方向上，从灯丝中点移动大约10 nm。这一运动的时间进程与力的产生过程一致，但慢于肌球蛋白细丝激活时的其他结构变化，包括肌球蛋白头部螺旋和轴向有序性的丧失以及肌球蛋白骨架的周期性变化。肌球蛋白头与肌动蛋白以与稳态等长收缩相同的构象附着的速度限制了力的发展速度；与附着步骤相比，肌球蛋白头的力产生更快。
Muscle contraction is driven by a change in the structure of the head domain of myosin, the "working stroke" that pulls the actin filaments toward the midpoint of the myosin filaments. This movement of the myosin heads can be measured very precisely in intact muscle cells by X-ray interference, but until now this technique has not been applied to physiological activation and force generation following electrical stimulation of muscle cells. By using this approach, we show that the long axes of the myosin head domains are roughly parallel to the filaments in resting muscle, with their center of mass offset by approximately 7 nm from the C terminus of the head domain. The observed mass distribution matches that seen in electron micrographs of isolated myosin filaments in which the heads are folded back toward the filament midpoint. Following electrical stimulation, the heads move by approximately 10 nm away from the filament midpoint, in the opposite direction to the working stroke. The time course of this motion matches that of force generation, but is slower than the other structural changes in the myosin filaments on activation, including the loss of helical and axial order of the myosin heads and the change in periodicity of the filament backbone. The rate of force development is limited by that of attachment of myosin heads to actin in a conformation that is the same as that during steadystate isometric contraction; force generation in the actin-attached head is fast compared with the attachment step.