Koubassova Natalia A, Tsaturyan A K
Institute of Mechanics, Lomonosov Moscow State University, Vorobjovy Gory, Moscow 119992, Russia.
Biophys J. 2002 Aug;83(2):1082-97. doi: 10.1016/S0006-3495(02)75232-6.
Available high-resolution structures of F-actin, myosin subfragment 1 (S1), and their complex, actin-S1, were used to calculate a 2D x-ray diffraction pattern from skeletal muscle in rigor. Actin sites occupied by myosin heads were chosen using a "principle of minimal elastic distortion energy" so that the 3D actin labeling pattern in the A-band of a sarcomere was determined by a single parameter. Computer calculations demonstrate that the total off-meridional intensity of a layer line does not depend on disorder of the filament lattice. The intensity of the first actin layer A1 line is independent of tilting of the "lever arm" region of the myosin heads. Myosin-based modulation of actin labeling pattern leads not only to the appearance of the myosin and "beating" actin-myosin layer lines in rigor diffraction patterns, but also to changes in the intensities of some actin layer lines compared to random labeling. Results of the modeling were compared to experimental data obtained from small bundles of rabbit muscle fibers. A good fit of the data was obtained without recourse to global parameter search. The approach developed here provides a background for quantitative interpretation of the x-ray diffraction data from contracting muscle and understanding structural changes underlying muscle contraction.
利用现有的F-肌动蛋白、肌球蛋白亚片段1（S1）及其复合物肌动蛋白-S1的高分辨率结构，计算出处于强直状态的骨骼肌的二维X射线衍射图谱。使用“最小弹性畸变能原理”选择被肌球蛋白头部占据的肌动蛋白位点，以便通过单个参数确定肌节A带中的三维肌动蛋白标记模式。计算机计算表明，层线的总离子午线强度不依赖于细丝晶格的无序度。第一条肌动蛋白层A1线的强度与肌球蛋白头部“杠杆臂”区域的倾斜无关。基于肌球蛋白的肌动蛋白标记模式调节不仅导致在强直衍射图谱中出现肌球蛋白和“跳动”的肌动蛋白-肌球蛋白层线，而且与随机标记相比，还导致一些肌动蛋白层线强度的变化。将建模结果与从兔肌纤维小束获得的实验数据进行比较。无需进行全局参数搜索就获得了数据的良好拟合。这里开发的方法为定量解释收缩肌肉的X射线衍射数据和理解肌肉收缩背后的结构变化提供了背景。
