Myosin filament structure in vertebrate smooth muscle.
Myosin filament structure in vertebrate smooth muscle.
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脊椎动物平滑肌中的肌球蛋白丝结构。
DOI：
10.1083/jcb.134.1.53
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发表时间：
1996-07
期刊：
影响因子：
--
通讯作者：
Craig R
中科院分区：
文献类型：
--
作者：
Xu JQ;Harder BA;Uman P;Craig R
脊椎动物平滑肌中肌球蛋白丝的体内结构尚不清楚。来自纯化的平滑肌肌球蛋白和一些完整平滑肌的研究的证据表明，它们可能有一个非螺旋的，侧极性排列的横桥。然而，横纹肌中肌球蛋白丝的双极螺旋结构特征在平滑肌中尚未被证明是错误的。我们已经使用EM来研究这个问题，在一个功能多样的平滑肌组（从血管，胃肠道，生殖和视觉系统）从哺乳动物，两栖动物和鸟类物种。生理条件下的完整肌肉，快速冷冻，然后冷冻替代，显示出许多肌球蛋白丝与一个正方形的骨干在横向轮廓。固定的、化学皮肤化的肌肉的横切面也显示出正方形的骨干，此外，只在正方形的两个相对侧上显示出突起（横桥）。从带皮平滑肌轻轻分离的细丝，通过负染色观察，显示在细丝的相对侧上以相反方向突出的14.5 nm重复的横桥。这样的细丝经受低离子强度条件显示裸露的细丝末端和肌球蛋白尾部沿细丝长度的反平行排列沿着。所有这些观察结果都与侧极结构相一致，并反对双极螺旋横桥排列。我们的结论是，肌球蛋白丝在所有平滑肌，无论功能，很可能是侧极性。这种结构可能是平滑肌大量收缩能力的重要因素。
The in vivo structure of the myosin filaments in vertebrate smooth muscle is unknown. Evidence from purified smooth muscle myosin and from some studies of intact smooth muscle suggests that they may have a nonhelical, side-polar arrangement of crossbridges. However, the bipolar, helical structure characteristic of myosin filaments in striated muscle has not been disproved for smooth muscle. We have used EM to investigate this question in a functionally diverse group of smooth muscles (from the vascular, gastrointestinal, reproductive, and visual systems) from mammalian, amphibian, and avian species. Intact muscle under physiological conditions, rapidly frozen and then freeze substituted, shows many myosin filaments with a square backbone in transverse profile. Transverse sections of fixed, chemically skinned muscles also show square backbones and, in addition, reveal projections (crossbridges) on only two opposite sides of the square. Filaments gently isolated from skinned smooth muscles and observed by negative staining show crossbridges with a 14.5-nm repeat projecting in opposite directions on opposite sides of the filament. Such filaments subjected to low ionic strength conditions show bare filament ends and an antiparallel arrangement of myosin tails along the length of the filament. All of these observations are consistent with a side-polar structure and argue against a bipolar, helical crossbridge arrangement. We conclude that myosin filaments in all smooth muscles, regardless of function, are likely to be side-polar. Such a structure could be an important factor in the ability of smooth muscles to contract by large amounts.