2-DIMENSIONAL TIME-RESOLVED X-RAY-DIFFRACTION STUDIES OF LIVE ISOMETRICALLY CONTRACTING FROG SARTORIUS MUSCLE
2-DIMENSIONAL TIME-RESOLVED X-RAY-DIFFRACTION STUDIES OF LIVE ISOMETRICALLY CONTRACTING FROG SARTORIUS MUSCLE
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DOI：
10.1007/bf00123096
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发表时间：
1993-06-01
影响因子：
2.7
通讯作者：
TOWNSANDREWS, E
中科院分区：
文献类型：
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作者：
BORDAS, J;DIAKUN, GP;TOWNSANDREWS, E
通过在英国同步辐射源（SERC，达雷斯伯里，实验室）收集高质量的时间分辨的二维X射线衍射图，从收缩的青蛙肌肉中获得结果。与等距张力生成相关的结构转变的条件下，在该条件下，三维秩序特征的休息状态是存在或不存在。在这两种情况下，新的层线出现在张力产生过程中，随后从激活事件的变化在细丝。与严格状态的“装饰”肌动蛋白层线相比，新层线的间距相似，但它们的强度有很大不同。我们的结论是，在收缩肌肉形成的肌动球蛋白复合物的结构是不一样的僵硬，虽然它是可能的，相互作用的网站是相同的。从静止到张力平台的过渡伴随着肌球蛋白层线的轴向间距增加约1.6%。这被解释为所产生的相互作用的肌球蛋白头的肌动球蛋白复合物的轴向配置。模型计算支持这一观点。我们认为，在收缩过程中形成的肌动球蛋白复合物的情况下，不能描述的衍射功能是厚或薄的细丝为基础。因此，在张力产生期间看到的层线被称为肌动球蛋白层线。它示出，这些层线可以被索引为约218.7 nm的最小轴向重复的约数。在考虑晶格无序效应后，第15和第21层AM层线的强度分别在14.58和10.4nm处随张力的增加而增加，表现出与张力增加相同的时间过程。然而，其他肌动球蛋白层线的强度增加和间距变化（这两种现象是相同的）的时间过程显示了对张力上升的实质性领先。这些发现表明，在张力上升之前形成的肌动球蛋白复合物是一种非张力产生状态，随后是复合物向张力产生状态的过渡。第15肌动球蛋白层线的强度增加，平行于张力上升，可以解释为假设在张力产生状态下，连接的头部相对于肌肉轴采取（轴向）比在休息或非张力产生状态下看到的更垂直的方向。这表明存在至少两种结构不同的相互作用的肌球蛋白头部构象。比较静止时肌球蛋白层线和张力平台时肌动球蛋白层线之间的螺旋强度的结果（测量到约2.6 nm的分辨率）被解释为表明肌动球蛋白复合物中的大多数肌球蛋白头部不进行平均值大于约3.0 nm的随机轴向旋转。从这一点我们得出结论，在相互作用的头部轴向秩序的程度必须至少是一样高，是休息的头部。
Results were obtained from contracting frog muscles by collecting high quality time-resolved, two-dimensional, X-ray diffraction patterns at the British Synchrotron Radiation Source (SERC, Daresbury, Laboratory). The structural transitions associated with isometric tension generation were recorded under conditions in which the three-dimensional order characteristic of the rest state is either present or absent. In both cases, new layer lines appear during tension generation, subsequent to changes from activation events in the thin filaments. Compared with the 'decorated' actin layer lines of the rigor state, the spacings of the new layer lines are similar whereas their intensities differ substantially. We conclude that in contracting muscle an actomyosin complex is formed whose structure is not like that in rigor, although it is possible that the interacting sites are the same. Transition from rest to plateau of tension is accompanied by approximately 1.6% increase in the axial spacing of the myosin layer lines. This is explained as arising from the axial disposition of the interacting myosin heads in the actomyosin complex. Model calculations are presented which support this view. We argue that in a situation where an actomyosin complex is formed during contraction, one cannot describe the diffraction features as being either thick or thin filament based. Accordingly, the layer lines seen during tension generation are referred to as actomyosin layer lines. It is shown that these layer lines can be indexed as submultiples of a minimum axial repeat of approximately 218.7 nm. After lattice disorder effects are taken into account, the intensity increases on the 15th and 21st AM layer lines at spacings of approximately 14.58 and 10.4 nm respectively, show the same time course as tension rise. However, the time course of the intensity increase of the other actomyosin layer lines and of the spacing change (which is the same for both phenomena) shows a substantial lead over tension rise. These findings suggest that the actomyosin complex formed prior to tension rise is a non-tension-generating state and that this is followed by a transition of the complex to a tension-generating state. The intensity increase in the 15th actomyosin layer line, which parallels tension rise, can be accounted for assuming that in the tension-generating state the attached heads adopt (axially) a more perpendicular orientation with respect to the muscle axis than is seen at rest or in the non-tension-generating state. This suggests the existence of at least two structurally distinct interacting myosin head conformations. The results of comparing the meridional intensities between the myosin layer lines at rest and the actomyosin layer lines at the plateau of tension (measured to a resolution of approximately 2.6 run) are interpreted to indicate that the majority of the myosin heads in the actomyosin complex do not perform random axial rotations with a mean value greater than approximately 3.0 nm. From this we conclude that the extent of axial order in the interacting heads must be at least as high as is that of resting heads.