Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405, USA.
Mol Biol Cell. 2010 Mar 15;21(6):989-1000. doi: 10.1091/mbc.e09-10-0852. Epub 2010 Jan 28.
Myosin-II (Myo2p) and tropomyosin are essential for contractile ring formation and cytokinesis in fission yeast. Here we used a combination of in vivo and in vitro approaches to understand how these proteins function at contractile rings. We find that ring assembly is delayed in Myo2p motor and tropomyosin mutants, but occurs prematurely in cells engineered to express two copies of myo2. Thus, the timing of ring assembly responds to changes in Myo2p cellular levels and motor activity, and the emergence of tropomyosin-bound actin filaments. Doubling Myo2p levels suppresses defects in ring assembly associated with a tropomyosin mutant, suggesting a role for tropomyosin in maximizing Myo2p function. Correspondingly, tropomyosin increases Myo2p actin affinity and ATPase activity and promotes Myo2p-driven actin filament gliding in motility assays. Tropomyosin achieves this by favoring the strong actin-bound state of Myo2p. This mode of regulation reflects a role for tropomyosin in specifying and stabilizing actomyosin interactions, which facilitates contractile ring assembly in the fission yeast system.
肌球蛋白-II（Myo2p）和原肌球蛋白是裂殖酵母收缩环形成和胞质分裂所必需的。在这里，我们使用体内和体外相结合的方法来了解这些蛋白质在收缩环中的作用。我们发现，肌球蛋白 II 马达和原肌球蛋白突变体中的环组装延迟，但在表达两个肌球蛋白 II 拷贝的细胞中过早出现。因此，环组装的时间响应于肌球蛋白 II 细胞水平和马达活性以及结合肌球蛋白 II 的肌动蛋白丝的出现的变化。肌球蛋白 II 水平加倍可抑制与原肌球蛋白突变体相关的环组装缺陷，这表明原肌球蛋白在最大限度地发挥肌球蛋白 II 功能方面发挥作用。相应地，原肌球蛋白增加肌球蛋白 II 肌动蛋白亲和力和 ATP 酶活性，并在运动分析中促进肌球蛋白 II 驱动的肌动蛋白丝滑行。原肌球蛋白通过有利于肌球蛋白 II 的强肌动蛋白结合状态来实现这一点。这种调节模式反映了原肌球蛋白在指定和稳定肌球蛋白 II 肌动蛋白相互作用中的作用，这有助于裂殖酵母系统中的收缩环组装。
