Skubiszak Ludmila
Nałęcz Institute of Biocybernetics and Biomedical Engineering of the Polish Academy of Sciences, Ks. Trojdena 4, 02-109 Warszawa, Poland; E-Mail:
Int J Mol Sci. 2011;12(4):2138-57. doi: 10.3390/ijms12042138. Epub 2011 Mar 29.
Computer simulation has uncovered the geometrical conditions under which the vertebrate striated muscle sarcomere can contract. First, all thick filaments should have identical structure, namely: three myosin cross-bridges, building a crown, should be aligned at angles of 0°, 120°, 180°, and the successive crowns and the two filament halves should be turned around 120°. Second, all thick filaments should act simultaneously. Third, coordination in action of the myosin cross-bridges should exist, namely: the three cross-bridges of a crown should act simultaneously and the cross-bridge crowns axially 43 and 14.333 nm apart should act, respectively, simultaneously and with a phase shift. Fifth, six thin filaments surrounding the thick filament should be turned around 180° to each other in each sarcomere half. Sixth, thin filaments should be oppositely oriented in relation to the sarcomere middle. Finally, the structure of each of the thin filaments should change in consequence of strong interaction with myosin heads, namely: the axial distance and the angular alignment between neighboring actin monomers should be, respectively, 2.867 nm and 168° instead of 2.75 nm and 166.15°. These conditions ensure the stereo-specific interaction between actin and myosin and good agreement with the data gathered by electron microscopy and X-ray diffraction methods. The results suggest that the force is generated not only by the myosin cross-bridges but also by the thin filaments; the former acts by cyclical unwrapping and wrapping the thick filament backbone, and the latter byelongation.
计算机模拟揭示了脊椎动物横纹肌肌节能够收缩的几何条件。首先，所有粗肌丝应具有相同的结构，即：构成冠状结构的三个肌球蛋白横桥应以0°、120°、180°的角度排列，并且相继的冠状结构以及粗肌丝的两半应绕轴旋转120°。其次，所有粗肌丝应同时起作用。第三，肌球蛋白横桥的作用应存在协调性，即：一个冠状结构的三个横桥应同时起作用，并且轴向相距43和14.333 nm的横桥冠状结构应分别同时起作用且有相位差。第五，在每个肌节的一半中，围绕粗肌丝的六条细肌丝应彼此绕轴旋转180°。第六，细肌丝应相对于肌节中部反向排列。最后，由于与肌球蛋白头部的强烈相互作用，每条细肌丝的结构应发生变化，即：相邻肌动蛋白单体之间的轴向距离和角度排列应分别为2.867 nm和168°，而不是2.75 nm和166.15°。这些条件确保了肌动蛋白和肌球蛋白之间的立体特异性相互作用，并与电子显微镜和X射线衍射方法收集的数据高度吻合。结果表明，力不仅由肌球蛋白横桥产生，也由细肌丝产生；前者通过周期性地解开和缠绕粗肌丝主干起作用，后者通过伸长起作用。
