Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington, USA.
Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, Virginia, USA.
Protein Sci. 2022 Jul;31(7):e4358. doi: 10.1002/pro.4358.
A transient increase in Ca concentration in sarcomeres is essential for their proper function. Ca drives striated muscle contraction via binding to the troponin complex of the thin filament to activate its interaction with the myosin thick filament. In addition to the troponin complex, the myosin essential light chain and myosin-binding protein C were also found to be Ca sensitive. However, the effects of Ca on the function of the tropomodulin family proteins involved in regulating thin filament formation have not yet been studied. Leiomodin, a member of the tropomodulin family, is an actin nucleator and thin filament elongator. Using pyrene-actin polymerization assay and transmission electron microscopy, we show that the actin nucleation activity of leiomodin is attenuated by Ca . Using circular dichroism and nuclear magnetic resonance spectroscopy, we demonstrate that the mostly disordered, negatively charged region of leiomodin located between its first two actin-binding sites binds Ca . We propose that Ca binding to leiomodin results in the attenuation of its nucleation activity. Our data provide further evidence regarding the role of Ca as an ultimate regulator of the ensemble of sarcomeric proteins essential for muscle function. SUMMARY STATEMENT: Ca fluctuations in striated muscle sarcomeres modulate contractile activity via binding to several distinct families of sarcomeric proteins. The effects of Ca on the activity of leiomodin-an actin nucleator and thin filament length regulator-have remained unknown. In this study, we demonstrate that Ca binds directly to leiomodin and attenuates its actin nucleating activity. Our data emphasizes the ultimate role of Ca in the regulation of the sarcomeric protein interactions.
肌节中 Ca 浓度的短暂增加对于其正常功能是必不可少的。Ca 通过与细肌丝上的肌钙蛋白复合物结合来驱动横纹肌收缩，从而激活其与肌球蛋白粗肌丝的相互作用。除了肌钙蛋白复合物外，肌球蛋白必需轻链和肌球蛋白结合蛋白 C 也被发现对 Ca 敏感。然而，Ca 对调节细肌丝形成的 tropomodulin 家族蛋白功能的影响尚未得到研究。雷奥莫丁（Leiomodin）是 tropomodulin 家族的一员，是一种肌动蛋白成核因子和细肌丝伸长因子。我们使用芘基肌动蛋白聚合测定法和透射电子显微镜显示，Ca 会减弱雷奥莫丁的肌动蛋白成核活性。我们通过圆二色性和核磁共振波谱法证明，位于其前两个肌动蛋白结合位点之间的雷奥莫丁的大部分无序、带负电荷的区域与 Ca 结合。我们提出，Ca 与雷奥莫丁结合会导致其成核活性减弱。我们的数据提供了进一步的证据，表明 Ca 作为调节肌肉功能所必需的肌节蛋白总体的最终调节剂的作用。摘要陈述：横纹肌肌节中的 Ca 波动通过结合几种不同家族的肌节蛋白来调节收缩活性。Ca 对肌动蛋白成核因子和细肌丝长度调节剂雷奥莫丁（Leiomodin）活性的影响尚不清楚。在这项研究中，我们证明 Ca 直接与雷奥莫丁结合并减弱其肌动蛋白成核活性。我们的数据强调了 Ca 在调节肌节蛋白相互作用中的最终作用。
