美国奥多明尼昂大学Howard D. White团队的一项最新研究探明了时间分辨低温电镜直接显示肌球蛋白的摆动机制。2025年4月9日出版的《自然》发表了这项成果。

为了解决这些问题，课题组研究人员对一种水解产物释放缓慢的肌球蛋白-5突变体进行了时间分辨低温电子显微镜（cryo-EM）观察。引物肌动球蛋白主要被捕获10与F-肌动蛋白混合后，肌动蛋白在120Ms，没有检测到大量的中间态。为了详细解释，低温电镜图用伪原子模型拟合。微小但关键的变化伴随着引物马达通过其较低的50 kda亚结构域与肌动蛋白结合，肌动蛋白结合的间隙打开，磷酸盐释放被禁止。氨基末端肌动蛋白与肌球蛋白的相互作用促进上部50kda亚结构域的旋转，关闭肌动蛋白结合间隙，并使磷酸盐释放。上50 kda子结构域和肌动蛋白之间相互作用的形成创造了有效作用力产生所需的强结合界面。肌凝蛋白-5杠杆摆动93°，主要沿着肌动蛋白轴，几乎没有扭曲。杠杆摆动的幅度与肌凝蛋白-5沿着acti7的典型步长相匹配。这些时间分辨的结构证明了摆动杆机制，阐明了力量击球的结构转变，并解决了几十年来关于肌凝蛋白如何产生运动的猜想。

据了解，肌凝蛋白通过与F-肌动蛋白1的相互作用在细胞中产生力量和运动。运动的产生被认为是通过肌动蛋白催化的肌球蛋白从ATP产生的启动（力量冲程前）状态到力量冲程后状态的转化，伴随着肌球蛋白杠杆的摆动。然而，最初的，引物肌动球蛋白状态从未被观察到，肌动蛋白催化肌球蛋白ATP酶活性的机制尚不清楚。

附：英文原文

Title: Swinging lever mechanism of myosin directly shown by time-resolved cryo-EM

Author: Klebl, David P., McMillan, Sean N., Risi, Cristina, Forgacs, Eva, Virok, Betty, Atherton, Jennifer L., Harris, Sarah A., Stofella, Michele, Winkelmann, Donald A., Sobott, Frank, Galkin, Vitold E., Knight, Peter J., Muench, Stephen P., Scarff, Charlotte A., White, Howard D.

Issue&Volume: 2025-04-09

Abstract: Myosins produce force and movement in cells through interactions with F-actin1. Generation of movement is thought to arise through actin-catalysed conversion of myosin from an ATP-generated primed (pre-powerstroke) state to a post-powerstroke state, accompanied by myosin lever swing2,3. However, the initial, primed actomyosin state has never been observed, and the mechanism by which actin catalyses myosin ATPase activity is unclear. Here, to address these issues, we performed time-resolved cryogenic electron microscopy (cryo-EM)4 of a myosin-5 mutant having slow hydrolysis product release5,6. Primed actomyosin was predominantly captured 10ms after mixing primed myosin with F-actin, whereas post-powerstroke actomyosin predominated at 120ms, with no abundant intermediate states detected. For detailed interpretation, cryo-EM maps were fitted with pseudo-atomic models. Small but critical changes accompany the primed motor binding to actin through its lower 50-kDa subdomain, with the actin-binding cleft open and phosphate release prohibited. Amino-terminal actin interactions with myosin promote rotation of the upper 50-kDa subdomain, closing the actin-binding cleft, and enabling phosphate release. The formation of interactions between the upper 50-kDa subdomain and actin creates the strong-binding interface needed for effective force production. The myosin-5 lever swings through 93°, predominantly along the actin axis, with little twisting. The magnitude of lever swing matches the typical step length of myosin-5 along actin7. These time-resolved structures demonstrate the swinging lever mechanism, elucidate structural transitions of the power stroke, and resolve decades of conjecture on how myosins generate movement.

DOI: 10.1038/s41586-025-08876-5

Source: https://www.nature.com/articles/s41586-025-08876-5