Crystal structures of human cardiac β-myosin IIS2-Δ provide insight into the functional role of the S2 subfragment
Crystal structures of human cardiac β-myosin IIS2-Δ provide insight into the functional role of the S2 subfragment
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DOI：
10.1073/pnas.0606741103
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发表时间：
2006-11-21
影响因子：
11.1
通讯作者：
Schlichting, Ilme
中科院分区：
文献类型：
--
作者：
Blankenfeldt, Wulf;Thoma, Nicolas H.;Schlichting, Ilme
肌球蛋白II是肌粗丝的主要成分。它由两个n端S1亚片段（“头”）组成，连接到一个长二聚体线圈棒。棒本身是双重对称的，但在灯丝中，两个头指向远离灯丝表面，因此不是等效的。这种对称性的破坏要求杆的初始部分，亚片段2 （S2）相对灵活。S2是一个重要的功能元件，参与平滑肌和横纹肌活动调节的多种机制。我们已经确定了人类心脏β -肌球蛋白II （S2- delta）的126个n端残基的晶体结构，包括WT和疾病相关的E924K突变体。S2-Delta是一种直平行的二聚体卷曲线圈，但WT-S2-Delta中有一条链的N端由于晶体接触而无序，表明局部结构不稳定。庞大的非规范侧链堆积在S2-Delta的N端a/d位置，导致局部不对称和轴向交错，这可能导致S1亚片段的不等效。此外，52具有保守的电荷分布，在S2-Delta内具有三个突出的负电位环，其中第一个环可能为平滑肌肌球蛋白在OFF状态下的“阻塞头”提供结合界面。许多疾病相关突变影响第二个带负电荷环的观察结果进一步表明，电荷相互作用通过肌球蛋白结合蛋白C在心肌活动调节中起重要作用。
Myosin II is the major component of the muscle thick filament. it consists of two N-terminal S1 subfragments ("heads") connected to a long dimeric coiled-coil rod. The rod is in itself twofold symmetric, but in the filament, the two heads point away from the filament surface and are therefore not equivalent. This breaking of symmetry requires the initial section of the rod, subfragment 2 (S2), to be relatively flexible. S2 is an important functional element, involved in various mechanisms by which the activity of smooth and striated muscle is regulated. We have determined crystal structures of the 126 N-terminal residues of S2 from human cardiac beta-myosin II (S2-Delta), of both WT and the disease-associated E924K mutant. S2-Delta is a straight parallel dimeric coiled coil, but the N terminus of one chain is disordered in WT-S2-Delta due to crystal contacts, indicative of unstable local structure. Bulky noncanonical side chains pack into a/d positions of S2-Delta's N terminus, leading to defined local asymmetry and axial stagger, which could induce nonequivalence of the S1 subfragments. Additionally, 52 possesses a conserved charge distribution with three prominent rings of negative potential within S2-Delta, the first of which may provide a binding interface for the "blocked head" of smooth muscle myosin in the OFF state. The observation that many disease-associated mutations affect the second negatively charged ring further suggests that charge interactions play an important role in regulation of cardiac muscle activity through myosin-binding protein C.