White S P, Cohen C, Phillips G N
Nature. 1987;325(6107):826-8. doi: 10.1038/325826a0.
Troponin, a Ca2+-sensitive complex, regulates the motions of tropomyosin on the thin filaments in many muscles. It has three subunits, each with a different architecture and function: TnC binds Ca2+; TnI binds to actin and inhibits contraction; and TnT binds one complex to each tropomyosin molecule. The troponin complex has an elongated shape with TnC and TnI forming a globular 'head' region and TnT a long (approximately 160 A) 'tail'. TnT binds to two widely separated regions of tropomyosin: the head region of the complex is near Cys 190 of tropomyosin and the tail region is near the overlapping joint that links the tropomyosin molecules into filaments. Here we report the X-ray structure determination at 17 A resolution of glutaraldehyde-treated tropomyosin crystals in which native troponin complex or fragments of TnT have been bound. Our results show that the amino-terminal tail end of TnT spans the head-to-tail joint of the tropomyosin filaments, and that the 'head' region of the whole troponin complex binds approximately 200 A away near residues 150-180 of the tropomyosin molecule.
肌钙蛋白是一种对Ca2+敏感的复合物，在许多肌肉中调节细肌丝上原肌球蛋白的运动。它有三个亚基，每个亚基都有不同的结构和功能：肌钙蛋白C（TnC）结合Ca2+；肌钙蛋白I（TnI）结合肌动蛋白并抑制收缩；肌钙蛋白T（TnT）将一个复合物与每个原肌球蛋白分子结合。肌钙蛋白复合物呈细长形，TnC和TnI形成一个球状的“头部”区域，TnT形成一条长（约160埃）的“尾巴”。TnT与原肌球蛋白的两个相距很远的区域结合：复合物的头部区域靠近原肌球蛋白的半胱氨酸190，尾巴区域靠近将原肌球蛋白分子连接成细丝的重叠接头。在此，我们报告了戊二醛处理的原肌球蛋白晶体在17埃分辨率下的X射线结构测定结果，其中已结合了天然肌钙蛋白复合物或TnT片段。我们的结果表明，TnT的氨基末端尾部跨越原肌球蛋白细丝的头对头接头，并且整个肌钙蛋白复合物的“头部”区域在原肌球蛋白分子的150 - 180位残基附近约200埃处结合。
