Myosin II molecules in the thick filaments of striated muscle form a structure in which the heads interact with each other and fold back onto the tail. This structure, the "interacting heads motif" (IHM), provides a mechanistic basis for the auto-inhibition of myosin in relaxed thick filaments. Similar IHM interactions occur in single myosin molecules of smooth and nonmuscle cells in the switched-off state. In addition to the interaction between the two heads, which inhibits their activity, the IHM also contains an interaction between the motor domain of one head and the initial part (subfragment 2, S2) of the tail. This is thought to be a crucial anchoring interaction that holds the IHM in place on the thick filament. S2 appears to cross the head at a specific location within a broader region of the motor domain known as the myosin mesa. Here, we show that the positive and negative charge distribution in this part of the mesa is complementary to the charge distribution on S2. We have designated this the "mesa trail" owing to its linear path across the mesa. We studied the structural sequence alignment, the location of charged residues on the surface of myosin head atomic models, and the distribution of surface charge potential along the mesa trail in different types of myosin II and in different species. The charge distribution in both the mesa trail and the adjacent S2 is relatively conserved. This suggests a common basis for IHM formation across different myosin IIs, dependent on attraction between complementary charged patches on S2 and the myosin head. Conservation from mammals to insects suggests that the mesa trail/S2 interaction plays a key role in the inhibitory function of the IHM.

中文翻译：

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台球轨迹和肌球蛋白II的相互作用的头模。

横纹肌的粗细丝中的肌球蛋白II分子形成一种结构，在这种结构中，头彼此相互作用并折回到尾巴上。这种结构称为“相互作用的头部基序”（IHM），为松弛的粗长丝中肌球蛋白的自动抑制提供了机理基础。在关闭状态下，平滑肌和非肌肉细胞的单个肌球蛋白分子中也会发生类似的IHM相互作用。除了两个头部之间的相互作用（这抑制了它们的活动）之外，IHM还包含一个头部的运动域与尾巴的初始部分（子片段2，S2）之间的相互作用。这被认为是将IHM固定在粗细丝上的关键锚固作用。S2似乎在称为肌球蛋白台面的运动区域的较宽区域内的特定位置横过头部。在这里，我们表明台面这一部分的正电荷分布和负电荷分布与S2上的电荷分布互补。由于其跨台面的线性路径，我们将其称为“台面路径”。我们研究了结构序列比对，肌球蛋白头部原子模型表面带电残基的位置，以及在不同类型的肌球蛋白II和不同物种中沿台面路径的表面电荷电位的分布。台面路径和相邻S2中的电荷分布相对保守。这表明跨不同肌球蛋白IIs形成IHM的共同基础，取决于S2上互补的带电荷斑块和肌球蛋白头的吸引力。