Activation of the myosin motors in fast-twitch muscle of the mouse is controlled by mechano-sensing in the myosin filaments.
Activation of the myosin motors in fast-twitch muscle of the mouse is controlled by mechano-sensing in the myosin filaments.
复制标题
DOI：
10.1113/jp283048
复制
发表时间：
2022-09
影响因子：
5.5
通讯作者：
Irving, Malcolm
中科院分区：
文献类型：
--
作者：
Hill, Cameron;Brunello, Elisabetta;Fusi, Luca;Ovejero, Jesus Garcia;Irving, Malcolm
静息肌肉中的肌凝蛋白马达通过以有序的螺旋阵列折叠肌凝蛋白丝的主干而失活，并且必须从该构象中释放以参与力的产生。两栖动物肌肉单纤维的时间分辨X射线衍射显示，在刺激开始时施加卸载缩短可以抑制肌球蛋白细丝的激活，这表明细丝是由机械应力激活的。在这里，我们利用小鼠整个指长伸肌在28°C下强直收缩，提高了该方法的信噪比。与肌凝蛋白丝激活相关的X射线信号的变化，包括与螺旋马达阵列相关的一阶肌凝蛋白层线的减少，与肌凝蛋白尾部在纤维主干中堆积相关的基于肌凝蛋白的反射间距的增加，以及与马达远离主干运动相关的1,1和1,0赤道反射比例的增加，通过在刺激开始时施加10 ms的卸载缩短而延迟。这些结果表明肌球蛋白丝主要是由丝应力激活，如在两栖动物肌肉。然而，在零负荷下检测到纤维活化的一小部分，这意味着部分纤维活化的独立机制。X射线干涉测量表明，在力发展开始时，肌凝蛋白运动构象发生了类似开关的变化，同时在肌凝蛋白丝中点附近的区域出现了短暂的运动紊乱，这表明丝区动力学也在其激活中起作用。小鼠指长伸肌中肌球蛋白丝的激活被从刺激开始施加的快速缩短所延迟。应激是这些肌肉中肌球蛋白丝激活的主要机制，但在零应激的电刺激下，丝的激活也有一小部分。肌凝蛋白马达在力发展早期迅速从折叠抑制构象切换到肌动蛋白附着力产生构象。哺乳动物骨骼肌粗纤维中的机械感应。时间分辨X射线衍射允许在完整的工作肌肉收缩期间跟踪含有肌球蛋白的粗丝和含有肌动蛋白的细丝的结构变化。在静止的肌肉（青色）中，由于没有钙与肌钙蛋白（六边形）结合，细纤维处于关闭状态，肌凝蛋白马达被折叠回以螺旋排列的粗纤维主干（灰色）所抑制。在高负荷收缩期间（紫色），大多数肌凝蛋白马达离开螺旋阵列，一些（绿色）与细丝结合产生力，而另一些（黄色）变得混乱。当在电刺激开始时施加一段时间的快速缩短，以保持肌肉上的负荷非常低（低负荷；连续的黑色力迹），几乎所有的马达都保持在螺旋折叠状态（灰色），即使细丝是打开的，两个钙离子（白色）与每个肌钙蛋白（六边形）结合。这些结果表明，哺乳动物骨骼肌肌球蛋白运动的激活是由粗丝中的机械应力控制的。
Myosin motors in resting muscle are inactivated by folding against the backbone of the myosin filament in an ordered helical array and must be released from that conformation to engage in force generation. Time‐resolved X‐ray diffraction from single fibres of amphibian muscle showed that myosin filament activation could be inhibited by imposing unloaded shortening at the start of stimulation, suggesting that filaments were activated by mechanical stress. Here we improved the signal‐to‐noise ratio of that approach using whole extensor digitorum longus muscles of the mouse contracting tetanically at 28°C. Changes in X‐ray signals associated with myosin filament activation, including the decrease in the first‐order myosin layer line associated with the helical motor array, increase in the spacing of a myosin‐based reflection associated with packing of myosin tails in the filament backbone, and increase in the ratio of the 1,1 and 1,0 equatorial reflections associated with movement of motors away from the backbone, were delayed by imposing 10‐ms unloaded shortening at the start of stimulation. These results show that myosin filaments are predominantly activated by filament stress, as in amphibian muscle. However, a small component of filament activation at zero load was detected, implying an independent mechanism of partial filament activation. X‐ray interference measurements indicated a switch‐like change in myosin motor conformation at the start of force development, accompanied by transient disordering of motors in the regions of the myosin filament near its midpoint, suggesting that filament zonal dynamics also play a role in its activation. Activation of myosin filaments in extensor digitorum longus muscles of the mouse is delayed by imposing rapid shortening from the start of stimulation. Stress is the major mechanism of myosin filament activation in these muscles, but there is a small component of filament activation during electrical stimulation at zero stress. Myosin motors switch rapidly from the folded inhibited conformation to the actin‐attached force‐generating conformation early in force development. Abstract figure legend Mechano‐sensing in the thick filament of mammalian skeletal muscle. Time‐resolved X‐ray diffraction allows changes in the structure of the myosin‐containing thick filaments and actin‐containing thin filaments during contraction to be followed in an intact working muscle. In resting muscle (cyan), thin filaments are OFF because no calcium is bound to troponin (hexagons), and myosin motors are inhibited by folding back against the thick filament backbone in a helical array (grey). During contraction at high load (purple), most myosin motors leave the helical array, and some (green) bind to the thin filament to generate force, whilst others (yellow) become disordered. When a period of rapid shortening is imposed at the start of electrical stimulation to keep the load on the muscle very low (low‐load; continuous black force trace), nearly all motors remain in the helical folded state (grey) even though the thin filament is ON and two calcium ions (white) are bound to each troponin (hexagons). These results show that activation of myosin motors in mammalian skeletal muscle is controlled by mechanical stress in the thick filament.