Lindhout Darrin A, Sykes Brian D
Canadian Institutes of Health Research Group in Protein Structure and Function and the Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
J Biol Chem. 2003 Jul 18;278(29):27024-34. doi: 10.1074/jbc.M302497200. Epub 2003 May 5.
Cardiac troponin C is the Ca2+-dependent switch for heart muscle contraction. Troponin C is associated with various other proteins including troponin I and troponin T. The interaction between the subunits within the troponin complex is of critical importance in understanding contractility. Following a Ca2+ signal to begin contraction, the inhibitory region of troponin I comprising residues Thr128-Arg147 relocates from its binding surface on actin to troponin C, triggering movement of troponin-tropomyosin within the thin filament and thereby freeing actin-binding site(s) for interactions with the myosin ATPase of the thick filament to generate the power stroke. The structure of calcium-saturated cardiac troponin C (C-domain) in complex with the inhibitory region of troponin I was determined using multinuclear and multidimensional nuclear magnetic resonance spectroscopy. The structure of this complex reveals that the inhibitory region adopts a helical conformation spanning residues Leu134-Lys139, with a novel orientation between the E- and H-helices of troponin C, which is largely stabilized by electrostatic interactions. By using isotope labeling, we have studied the dynamics of the protein and peptide in the binary complex. The structure of this inhibited complex provides a framework for understanding into interactions within the troponin complex upon heart contraction.
心肌肌钙蛋白C是心肌收缩的钙离子依赖性开关。肌钙蛋白C与包括肌钙蛋白I和肌钙蛋白T在内的多种其他蛋白质相关联。肌钙蛋白复合物中亚基之间的相互作用对于理解收缩性至关重要。在钙离子信号引发收缩后，肌钙蛋白I包含苏氨酸128 - 精氨酸147残基的抑制区域从其在肌动蛋白上的结合表面重新定位到肌钙蛋白C，触发细肌丝内肌钙蛋白 - 原肌球蛋白的移动，从而释放肌动蛋白结合位点以与粗肌丝的肌球蛋白ATP酶相互作用，产生动力冲程。利用多核和多维核磁共振光谱法确定了与肌钙蛋白I抑制区域复合的钙饱和心肌肌钙蛋白C（C结构域）的结构。该复合物的结构表明，抑制区域呈现跨越亮氨酸134 - 赖氨酸139残基的螺旋构象，在肌钙蛋白C的E螺旋和H螺旋之间具有新的取向，这在很大程度上通过静电相互作用得以稳定。通过使用同位素标记，我们研究了二元复合物中蛋白质和肽的动力学。这种抑制复合物的结构为理解心脏收缩时肌钙蛋白复合物内的相互作用提供了一个框架。
