TROPOMODULIN IS ASSOCIATED WITH THE FREE (POINTED) ENDS OF THE THIN-FILAMENTS IN RAT SKELETAL-MUSCLE
TROPOMODULIN IS ASSOCIATED WITH THE FREE (POINTED) ENDS OF THE THIN-FILAMENTS IN RAT SKELETAL-MUSCLE
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DOI：
10.1083/jcb.120.2.411
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发表时间：
1993-01-01
影响因子：
7.8
通讯作者：
DANIELS, MP
中科院分区：
文献类型：
--
作者：
FOWLER, VM;SUSSMANN, MA;DANIELS, MP
骨骼肌肌节中细丝的长度和空间组织得到精确维持，并且对于有效的肌肉收缩是必不可少的。虽然骨骼肌肌节的主要结构成分已经得到很好的表征，但调节细丝长度和空间组织的机制还不清楚。原肌调节蛋白是一种新的，40.6 kD的原肌球蛋白结合蛋白，从人红细胞膜骨架，结合到红细胞原肌球蛋白的一端，并阻止头到尾的原肌球蛋白分子的协会沿着肌动蛋白丝。在这里，我们表明，大鼠腰大肌骨骼肌含有基于免疫反应性，SDS凝胶上相同的表观流动性，并结合肌肉原肌球蛋白的能力。结果从免疫荧光标记的分离肌原纤维在休息和拉伸长度使用抗红细胞原调节蛋白抗体表明，原调节蛋白是本地化或附近的自由（尖）端的细丝，这种本地化是不依赖于肌球蛋白粗丝的存在。从肌原纤维中提取肌球蛋白后获得的上清液和颗粒的免疫印迹也表明原调节蛋白仍然与细丝相关。在肌原纤维中，每根细丝存在1.2-1.6个拷贝的肌肉原调节蛋白，支持了一个或两个原调节蛋白分子可能与每根细丝尖端的两个末端原肌球蛋白分子结合的可能性。尽管许多蛋白质与Z盘上细丝的倒刺末端相关，但原调节蛋白是第一种特异性位于细丝尖端或尖端附近的蛋白质。我们建议，原调节蛋白可能帽原肌球蛋白聚合物在尖端的细丝，并发挥作用，在调节细丝长度。
The length and spatial organization of thin filaments in skeletal muscle sarcomeres are precisely maintained and are essential for efficient muscle contraction. While the major structural components of skeletal muscle sarcomeres have been well characterized, the mechanisms that regulate thin filament length and spatial organization are not well understood. Tropomodulin is a new, 40.6-kD tropomyosin-binding protein from the human erythrocyte membrane skeleton that binds to one end of erythrocyte tropomyosin and blocks head-to-tail association of tropomyosin molecules along actin filaments. Here we show that rat psoas skeletal muscle contains tropomodulin based on immunoreactivity, identical apparent mobility on SDS gels, and ability to bind muscle tropomyosin. Results from immunofluorescence labeling of isolated myofibrils at resting and stretched lengths using antierythrocyte tropomodulin antibodies indicate that tropomodulin is localized at or near the free (pointed) ends of the thin filaments; this localization is not dependent on the presence of myosin thick filaments. Immunoblotting of supernatants and pellets obtained after extraction of myosin from myofibrils also indicates that tropomodulin remains associated with the thin filaments. 1.2-1.6 copies of muscle tropomodulin are present per thin filament in myofibrils, supporting the possibility that one or two tropomodulin molecules may be associated with the two terminal tropomyosin molecules at the pointed end of each thin filament. Although a number of proteins are associated with the barbed ends of the thin filaments at the Z disc, tropomodulin is the first protein to be specifically located at or near the pointed ends of the thin filaments. We propose that tropomodulin may cap the tropomyosin polymers at the pointed end of the thin filament and play a role in regulating thin filament length.