Division of Cell Biology and Imaging, Department of Radiology, University of Massachusetts Medical School, Worcester, MA.
Department of Cellular and Molecular Biology, University of Texas Health Science Center at Tyler, Tyler, TX.
J Gen Physiol. 2019 Sep 2;151(9):1081-1093. doi: 10.1085/jgp.201912431. Epub 2019 Aug 6.
Myosin II is a motor protein with two heads and an extended tail that plays an essential role in cell motility. Its active form is a polymer (myosin filament) that pulls on actin to generate motion. Its inactive form is a monomer with a compact structure (10S sedimentation coefficient), in which the tail is folded and the two heads interact with each other, inhibiting activity. This conformation is thought to function in cells as an energy-conserving form of the molecule suitable for storage as well as transport to sites of filament assembly. The mechanism of inhibition of the compact molecule is not fully understood. We have performed a 3-D reconstruction of negatively stained 10S myosin from smooth muscle in the inhibited state using single-particle analysis. The reconstruction reveals multiple interactions between the tail and the two heads that appear to trap ATP hydrolysis products, block actin binding, hinder head phosphorylation, and prevent filament formation. Blocking these essential features of myosin function could explain the high degree of inhibition of the folded form of myosin thought to underlie its energy-conserving function in cells. The reconstruction also suggests a mechanism for unfolding when myosin is activated by phosphorylation.
肌球蛋白 II 是一种具有两个头部和一个延伸尾部的运动蛋白，在细胞运动中起着至关重要的作用。其活性形式是一种聚合物（肌球蛋白丝），可拉动肌动蛋白产生运动。其非活性形式是一种具有紧凑结构的单体（10S 沉降系数），其中尾部折叠，两个头部相互作用，抑制活性。这种构象被认为在细胞中作为一种节能形式的分子，适合储存以及运输到丝组装的部位。紧凑分子抑制的机制尚未完全理解。我们使用单颗粒分析对抑制状态下平滑肌中的负染 10S 肌球蛋白进行了 3D 重建。重建揭示了尾部和两个头部之间的多种相互作用，这些相互作用似乎捕获了 ATP 水解产物，阻止肌动蛋白结合，阻碍头部磷酸化，并防止丝形成。阻止这些肌球蛋白功能的基本特征可以解释折叠形式的肌球蛋白被认为在细胞中具有节能功能的高度抑制。该重建还提出了一种机制，即当肌球蛋白通过磷酸化激活时，其解折叠。
