Myosin light chain phosphorylation enhances contraction of heart muscle via structural changes in both thick and thin filaments
Myosin light chain phosphorylation enhances contraction of heart muscle via structural changes in both thick and thin filaments
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DOI：
10.1073/pnas.1602776113
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发表时间：
2016-05-24
影响因子：
11.1
通讯作者：
Irving, Malcolm
中科院分区：
文献类型：
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作者：
Kampourakis, Thomas;Sun, Yin-Biao;Irving, Malcolm
心肌收缩是由钙与含肌动蛋白的细丝结合而触发的，但受含肌球蛋白的粗丝结构变化的调节。我们使用肌球蛋白调节轻链(CRLC)的磷酸化来阐明大鼠右室去膜小梁中粗丝介导的收缩调节机制。正如双功能罗丹明探针在cRLC上所报道的那样，cRLC的磷酸化增强了活性和钙敏感性，并改变了粗丝结构：肌球蛋白头域变得更加垂直于细丝轴。CRLC的磷酸化对粗丝结构和钙敏感性的影响可以通过增加肌节长度或删除cRLC的N端来模拟。粗丝结构的变化与钙离子浓度或cRLC磷酸化程度高度相关。未磷酸化的肌球蛋白头部的探针报告了当相邻头部被磷酸化时类似的结构变化，直接证明了肌球蛋白头部之间的信号传递。此外，对肌钙蛋白的探测表明，cRLC磷酸化的钙增敏作用是由细丝介导的，揭示了粗丝和细丝之间的信号通路，当激活力被Blebbistatin阻断时，这种信号通路仍然存在。这些结果表明，粗丝和细丝的协调和协同结构变化是心脏收缩能力的生理调节的基础。这种收缩调节的综合双丝概念可能有助于理解与心脏病相关的两种纤维蛋白成分突变的功能影响。
Contraction of heart muscle is triggered by calcium binding to the actin-containing thin filaments but modulated by structural changes in the myosin-containing thick filaments. We used phosphorylation of the myosin regulatory light chain (cRLC) by the cardiac isoform of its specific kinase to elucidate mechanisms of thick filament-mediated contractile regulation in demembranated trabeculae from the rat right ventricle. cRLC phosphorylation enhanced active force and its calcium sensitivity and altered thick filament structure as reported by bifunctional rhodamine probes on the cRLC: the myosin head domains became more perpendicular to the filament axis. The effects of cRLC phosphorylation on thick filament structure and its calcium sensitivity were mimicked by increasing sarcomere length or by deleting the N terminus of the cRLC. Changes in thick filament structure were highly cooperative with respect to either calcium concentration or extent of cRLC phosphorylation. Probes on unphosphorylated myosin heads reported similar structural changes when neighboring heads were phosphorylated, directly demonstrating signaling between myosin heads. Moreover probes on troponin showed that calcium sensitization by cRLC phosphorylation is mediated by the thin filament, revealing a signaling pathway between thick and thin filaments that is still present when active force is blocked by Blebbistatin. These results show that coordinated and cooperative structural changes in the thick and thin filaments are fundamental to the physiological regulation of contractility in the heart. This integrated dual-filament concept of contractile regulation may aid understanding of functional effects of mutations in the protein components of both filaments associated with heart disease.