Wang Tianbang, Nayak Arnab, Kraft Theresia, Amrute-Nayak Mamta
Institute of Molecular and Cell Physiology, Hannover Medical School, 30625, Hannover, Germany.
Small. 2024 Dec;20(51):e2406865. doi: 10.1002/smll.202406865. Epub 2024 Oct 7.
Myosins are ATP-powered, force-generating motor proteins involved in cardiac and muscle contraction. The external load experienced by the myosins modulates and coordinates their function in vivo. Here, this study investigates the tension-sensing mechanisms of rabbit native β-cardiac myosin (βM-II) and slow skeletal myosins (SolM-II) that perform in different physiological settings. Using mobile optical tweezers with a square wave-scanning mode, a range of external assisting and resisting loads from 0 to 15 pN is exerted on single myosin molecules as they interact with the actin filament. Influenced of load on specific strongly-bound states in the cross-bridge cycle is examined by adjusting the [ATP]. The results implies that the detachment kinetics of actomyosin ADP.Pi strongly-bound force-generating state are load sensitive. Low assisting load accelerates, while the resisting load hinders the actomyosin detachment, presumably, by slowing both the Pi and ADP release. However, under both high assisting and resisting load, the rate of actomyosin dissociation decelerates. The transition from actomyosin ADP.Pi to ADP state appears to occur with a higher probability for βM-II than SolM-II. This study interpret that dissociation of at least three strongly-bound actomyosin states are load-sensitive and may contribute to functional diversity among different myosins.
肌球蛋白是由ATP驱动、产生力的马达蛋白，参与心脏和肌肉收缩。肌球蛋白在体内所承受的外部负荷会调节并协调其功能。在此，本研究调查了在不同生理环境中发挥作用的兔天然β-心脏肌球蛋白（βM-II）和慢骨骼肌肌球蛋白（SolM-II）的张力传感机制。使用具有方波扫描模式的移动光镊，在单个肌球蛋白分子与肌动蛋白丝相互作用时，对其施加0至15皮牛顿的一系列外部辅助和阻力负荷。通过调节[ATP]来研究负荷对横桥循环中特定强结合状态的影响。结果表明，肌动球蛋白ADP·Pi强结合力产生状态的解离动力学对负荷敏感。低辅助负荷会加速，而阻力负荷会阻碍肌动球蛋白解离，推测是通过减缓Pi和ADP的释放。然而，在高辅助负荷和阻力负荷下，肌动球蛋白解离速率都会减慢。βM-II从肌动球蛋白ADP·Pi转变为ADP状态的概率似乎高于SolM-II。本研究解释说，至少三种强结合肌动球蛋白状态的解离对负荷敏感，可能导致不同肌球蛋白之间的功能多样性。
