Hodgkinson J L, Marston S B, Craig R, Vibert P, Lehman W
Imperial College School of Medicine, National Heart and Lung Institute, London, United Kingdom.
Biophys J. 1997 Jun;72(6):2398-404. doi: 10.1016/S0006-3495(97)78885-4.
Caldesmon inhibits actomyosin ATPase and filament sliding in vitro, and therefore may play a role in modulating smooth and non-muscle motile activities. A bacterially expressed caldesmon fragment, 606C, which consists of the C-terminal 150 amino acids of the intact molecule, possesses the same inhibitory properties as full-length caldesmon and was used in our structural studies to examine caldesmon function. Three-dimensional image reconstruction was carried out from electron micrographs of negatively stained, reconstituted thin filaments consisting of actin and smooth muscle tropomyosin both with and without added 606C. Helically arranged actin monomers and tropomyosin strands were observed in both cases. In the absence of 606C, tropomyosin adopted a position on the inner edge of the outer domain of actin monomers, with an apparent connection to sub-domain 1 of actin. In 606C-containing filaments that inhibited acto-HMM ATPase activity, tropomyosin was found in a different position, in association with the inner domain of actin, away from the majority of strong myosin binding sites. The effect of caldesmon on tropomyosin position therefore differs from that of troponin on skeletal muscle filaments, implying that caldesmon and troponin act by different structural mechanisms.
钙调蛋白在体外可抑制肌动球蛋白ATP酶及细丝滑动，因此可能在调节平滑肌和非肌肉运动活性中发挥作用。一种细菌表达的钙调蛋白片段606C，由完整分子的C端150个氨基酸组成，具有与全长钙调蛋白相同的抑制特性，并在我们的结构研究中用于检测钙调蛋白的功能。对由肌动蛋白和平滑肌原肌球蛋白组成的、添加或未添加606C的负染重组细丝的电子显微照片进行三维图像重建。在两种情况下均观察到螺旋排列的肌动蛋白单体和原肌球蛋白链。在没有606C的情况下，原肌球蛋白位于肌动蛋白单体外部结构域的内边缘位置，与肌动蛋白的亚结构域1有明显连接。在抑制肌动蛋白-重酶解肌球蛋白ATP酶活性的含606C细丝中，发现原肌球蛋白处于不同位置，与肌动蛋白的内部结构域相关联，远离大多数强肌球蛋白结合位点。因此，钙调蛋白对原肌球蛋白位置的影响不同于肌钙蛋白对骨骼肌细丝的影响，这意味着钙调蛋白和肌钙蛋白通过不同的结构机制起作用。
