Lehman W, Vibert P, Uman P, Craig R
Department of Physiology, Boston University School of Medicine, Massachusetts 02118, USA.
J Mol Biol. 1995 Aug 11;251(2):191-6. doi: 10.1006/jmbi.1995.0425.
Although widely accepted, the steric-blocking model of vertebrate skeletal muscle regulation has not been confirmed. Previous attempts to directly visualize tropomyosin in relaxed skeletal muscle and demonstrate that it interferes with the crossbridge-thin filament contractile cycle were unsuccessful. In the work reported here, tropomyosin was resolved in electron micrographs of native thin filaments isolated from relaxed vertebrate striated muscle. Three-dimensional helical reconstructions of these filaments showed continuous narrow strands of density, representing tropomyosin, which followed the outer domains of successive actin monomers. The results obtained from fitting the atomic model of filamentous actin to these reconstructions illustrate, and are consistent with, the mechanism of steric-blocking, since tropomyosin was found to be positioned on the actin surface of thin filaments over clusters of identifiable amino acids required for myosin crossbridge docking.
尽管脊椎动物骨骼肌调节的空间位阻模型已被广泛接受，但尚未得到证实。此前试图直接观察松弛状态下骨骼肌中的原肌球蛋白，并证明其干扰横桥-细肌丝收缩循环的尝试均未成功。在本文报道的研究中，从松弛的脊椎动物横纹肌中分离出的天然细肌丝的电子显微照片中分辨出了原肌球蛋白。对这些细肌丝的三维螺旋重建显示出连续的狭窄密度带，代表原肌球蛋白，其沿着连续肌动蛋白单体的外部结构域分布。将丝状肌动蛋白的原子模型与这些重建结果进行拟合得到的结果说明了空间位阻机制，并且与之相符，因为发现原肌球蛋白位于细肌丝的肌动蛋白表面上，覆盖着肌球蛋白横桥对接所需的可识别氨基酸簇。
