De Nicola Gianfelice, Burkart Christoph, Qiu Feng, Agianian Bogos, Labeit Siegfried, Martin Stephen, Bullard Belinda, Pastore Annalisa
Molecular Structure Division, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom.
Structure. 2007 Jul;15(7):813-24. doi: 10.1016/j.str.2007.05.007.
To gain a molecular description of how muscles can be activated by mechanical stretch, we have solved the structure of the calcium-loaded F1 isoform of troponin C (TnC) from Lethocerus and characterized its interactions with troponin I (TnI). We show that the presence of only one calcium cation in the fourth EF hand motif is sufficient to induce an open conformation in the C-terminal lobe of F1 TnC, in contrast with what is observed in vertebrate muscle. This lobe interacts in a calcium-independent way both with the N terminus of TnI and, with lower affinity, with a region of TnI equivalent to the switch and inhibitory peptides of vertebrate muscles. Using both synthetic peptides and recombinant proteins, we show that the N lobe of F1 TnC is not engaged in interactions with TnI, excluding a regulatory role of this domain. These findings provide insights into mechanically stimulated muscle contraction.
为了从分子层面描述肌肉如何通过机械拉伸被激活，我们解析了来自大田鳖的钙负载肌钙蛋白C（TnC）F1亚型的结构，并对其与肌钙蛋白I（TnI）的相互作用进行了表征。我们发现，与脊椎动物肌肉中观察到的情况相反，在第四个EF手基序中仅存在一个钙阳离子就足以诱导F1 TnC C端叶形成开放构象。该叶以不依赖钙的方式与TnI的N端相互作用，并且以较低亲和力与TnI中相当于脊椎动物肌肉开关肽和抑制肽的区域相互作用。使用合成肽和重组蛋白，我们表明F1 TnC的N叶不参与与TnI的相互作用，排除了该结构域的调节作用。这些发现为机械刺激的肌肉收缩提供了见解。
