Cooperation between the two heads of smooth muscle myosin is essential for full activation of the motor function by phosphorylation.
Cooperation between the two heads of smooth muscle myosin is essential for full activation of the motor function by phosphorylation.
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DOI：
10.1021/bi400554s
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发表时间：
2013-08
期刊：
影响因子：
2.9
通讯作者：
Rong-Na Ma;K. Mabuchi;Jing Li;Zekuan Lu;Chih‐Lueh A. Wang;Xiang-dong Li
中科院分区：
文献类型：
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作者：
Rong-Na Ma;K. Mabuchi;Jing Li;Zekuan Lu;Chih‐Lueh A. Wang;Xiang-dong Li
肌球蛋白(SMM)的运动功能是由SMM重链颈部的调节轻链(RLC)的磷酸化来调节的。一般认为，未磷酸化的RLC可引起两头之间以及头尾之间的相互作用，从而抑制SMM的运动活动，而RLC的磷酸化则阻断这些相互作用，从而逆转这种抑制，使运动活动恢复到最大值。该模型的一个假设是单头SMM是完全活跃的，与磷酸化无关。为了重新评估这一模型，我们生产了一些具有不同长度的螺旋线圈的SMM结构，并检查了它们的结构和调节。通过这些结构，我们确定了螺旋线圈钥匙中用于形成稳定的双头结构的片段。与目前的模型一致，我们发现未磷酸化的SMM的肌动蛋白激活的ATPase活性随着卷曲线圈的缩短而增加。然而，与目前的模型相反，我们发现磷酸化的SMM的肌动蛋白激活的ATPase活性随着卷曲长度的缩短而降低，只有稳定的双头SMM才能被磷酸化完全激活。这些结果表明，单头SMM既不完全活跃，也不完全被抑制。基于我们的发现，我们认为两个头部之间的合作是必不可少的，不仅对于抑制非磷酸化的SMM，而且对于激活磷酸化的SMM也是必要的。
The motor function of smooth muscle myosin (SmM) is regulated by phosphorylation of the regulatory light chain (RLC) bound to the neck region of the SmM heavy chain. It is generally accepted that unphosphorylated RLC induces interactions between the two heads and between the head and the tail, thus inhibiting the motor activity of SmM, whereas phosphorylation of RLC interrupts those interactions, thus reversing the inhibition and restoring the motor activity to the maximal value. One assumption of this model is that single-headed SmM is fully active regardless of phosphorylation. To re-evaluate this model, we produced a number of SmM constructs with coiled coils of various lengths and examined their structure and regulation. With these constructs we identified the segment in the coiled-coil key for the formation of a stable double-headed structure. In agreement with the current model, we found that the actin-activated ATPase activity of unphosphorylated SmM increased with shortening of the coiled-coil. However, contrary to the current model, we found that the actin-activated ATPase activity of phosphorylated SmM decreased with shortening coiled-coil and only the stable double-headed SmM was fully activated by phosphorylation. These results indicate that single-headed SmM is neither fully active nor fully inhibited. Based on our findings, we propose that cooperation between the two heads is essential, not only for the inhibition of unphosphorylated SmM, but also for the activation of phosphorylated SmM.