Nature. 2016 Jun 30;534(7609):724-8. doi: 10.1038/nature18295. Epub 2016 Jun 20.
The interaction of myosin with actin filaments is the central feature of muscle contraction and cargo movement along actin filaments of the cytoskeleton. The energy for these movements is generated during a complex mechanochemical reaction cycle. Crystal structures of myosin in different states have provided important structural insights into the myosin motor cycle when myosin is detached from F-actin. The difficulty of obtaining diffracting crystals, however, has prevented structure determination by crystallography of actomyosin complexes. Thus, although structural models exist of F-actin in complex with various myosins, a high-resolution structure of the F-actin–myosin complex is missing. Here, using electron cryomicroscopy, we present the structure of a human rigor actomyosin complex at an average resolution of 3.9 Å. The structure reveals details of the actomyosin interface, which is mainly stabilized by hydrophobic interactions. The negatively charged amino (N) terminus of actin interacts with a conserved basic motif in loop 2 of myosin, promoting cleft closure in myosin. Surprisingly, the overall structure of myosin is similar to rigor-like myosin structures in the absence of F-actin, indicating that F-actin binding induces only minimal conformational changes in myosin. A comparison with pre-powerstroke and intermediate (Pi-release) states of myosin allows us to discuss the general mechanism of myosin binding to F-actin. Our results serve as a strong foundation for the molecular understanding of cytoskeletal diseases, such as autosomal dominant hearing loss and diseases affecting skeletal and cardiac muscles, in particular nemaline myopathy and hypertrophic cardiomyopathy.
肌球蛋白与肌动蛋白丝的相互作用是肌肉收缩和细胞骨架中肌动蛋白丝上货物运动的核心特征。这些运动的能量是在一个复杂的机械化学反应循环中产生的。肌球蛋白在不同状态下的晶体结构为肌球蛋白脱离 F-肌动蛋白时的肌球蛋白马达循环提供了重要的结构见解。然而，获得衍射晶体的困难阻碍了肌球蛋白肌动蛋白复合物的晶体学结构测定。因此，尽管存在与各种肌球蛋白结合的 F-肌动蛋白的结构模型，但缺少 F-肌动蛋白-肌球蛋白复合物的高分辨率结构。在这里，我们使用电子冷冻显微镜，以平均分辨率 3.9 Å 呈现了一个人类僵硬肌球蛋白肌动蛋白复合物的结构。该结构揭示了肌球蛋白肌动蛋白界面的细节，该界面主要由疏水相互作用稳定。肌动蛋白的带负电荷的氨基（N）末端与肌球蛋白环 2中的保守碱性基序相互作用，促进肌球蛋白的裂隙闭合。令人惊讶的是，肌球蛋白的整体结构与缺乏 F-肌动蛋白的僵硬样肌球蛋白结构相似，这表明 F-肌动蛋白结合仅在肌球蛋白中诱导最小的构象变化。与预功 stroke 和中间（Pi 释放）状态的肌球蛋白进行比较，使我们能够讨论肌球蛋白与 F-肌动蛋白结合的一般机制。我们的结果为细胞骨架疾病（如常染色体显性遗传性听力损失以及影响骨骼和心肌的疾病，特别是杆状体肌病和肥厚型心肌病）的分子理解提供了坚实的基础。
