Electron tomography of swollen rigor fibers of insect flight muscle reveals a short and variably angled S2 domain
Electron tomography of swollen rigor fibers of insect flight muscle reveals a short and variably angled S2 domain
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DOI：
10.1016/j.jmb.2006.07.084
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发表时间：
2006-09-29
影响因子：
5.6
通讯作者：
Taylor, Kenneth A.
中科院分区：
文献类型：
--
作者：
Liu, Jun;Wu, Shenping;Taylor, Kenneth A.
亚片段2（S2），将两个肌球蛋白头连接到粗丝骨架的片段，可以作为一个向外摆动的适配器，允许横桥进入肌动蛋白，作为横桥的弹性成分，并作为平滑肌中横桥磷酸化调节开关的一部分。低盐膨胀增加了许多横桥的丝间间距（从52 nm到67 nm）。将actoS 1原子模型对接到可分配给S2的片段的角度的EM断层图像中。对应分析1831 38.7 nm的crossbridge重复分组自相似的形式，类平均值可以计算。通过使用acto-SI原子拟合的类平均值显示暴露的S2的角度和长度的可变性的全范围，而S2通过将卷曲螺旋的长度拟合到未平均的个体重复来建模。该混合建模示出了S2系链沿着厚细丝（除了锥形端部附近）的平均长度类似于10 nm，或S2总长度的16%，其中角度范围包括轴向90度和方位角120度。S2角的大范围表明，一些刚性桥产生的正向力必须由其他产生阻力的力平衡。短拴系段澄清限制的功能，S2在适应可变的肌球蛋白头访问肌动蛋白。我们认为，S2的短长度也可能有利于IFM松弛的粗丝分子间的头-头相互作用。(c)2006爱思唯尔有限公司保留所有权利。
Subfragment 2 (S2), the segment that links the two myosin heads to the thick filament backbone, may serve as a swing-out adapter allowing crossbridge access to actin, as the elastic component of crossbridges and as part of a phosphorylation-regulated on-off switch for crossbridges in smooth muscle. Low-salt expansion increases interfilament spacing (from 52 nm to 67 nm) of many crossbridges. Docking an actoS1 atomic model into EM tomograms of angle assignable to a segment of S2. Correspondence analysis of 1831 38.7 nm crossbridge repeats grouped self-similar forms from which class averages could be computed. The full range of the variability in angles and lengths of exposed S2 was displayed by using class averages for atomic fittings of acto-SI, while S2 was modeled by fitting a length of coiled-coil to unaveraged individual repeats. This hybrid modeling shows that the average length of S2 tethers along the thick filament (except near the tapered ends) is similar to 10 nm, or 16% of S2's total length, with an angular range encompassing 90 degrees axially and 120 degrees azimuthally. The large range of S2 angles indicates that some rigor bridges produce positive force that must be balanced by others producing drag force. The short tethering segment clarifies constraints on the function of S2 in accommodating variable myosin head access to actin. We suggest that the short length of S2 may also favor intermolecular head-head interactions in IFM relaxed thick filaments. (c) 2006 Elsevier Ltd. All rights reserved.