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首页> 外文期刊>Scientific reports. >Structural Dynamics of the N-Extension of Cardiac Troponin I Complexed with Troponin C by Site-Directed Spin Labeling Electron Paramagnetic Resonance
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Structural Dynamics of the N-Extension of Cardiac Troponin I Complexed with Troponin C by Site-Directed Spin Labeling Electron Paramagnetic Resonance

机译：通过地点针对旋转标记电子顺磁共振对肌钙蛋白C复合的心肌肌钙蛋白的N-延伸的结构动力学

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The secondary structure of the N-extension of cardiac troponin I (cTnI) was determined by measuring the distance distribution between spin labels attached to the i and i?+?4 residues: 15/19, 23/27, 27/31, 35/39, and 43/47. All of the EPR spectra of these regions in the monomeric state were broadened and had a amplitude that was reduced by two-thirds of that of the single spin-labeled spectra and was fit by two residual distance distributions, with a major distribution one spreading over the range from 1 to 2.5?nm and the other minor peak at 0.9?nm. Only slight or no obvious changes were observed when the extension was bound to cTnC in the cTnI-cTnC complex at 0.2?M KCl. However, at 0.1?M KCl, residues 43/47, located at the PKC phosphorylation sites Ser42/44 on the boundary of the extension, exclusively exhibited a 0.9?nm peak, as expected from α-helix in the crystal structure, in the complex. Furthermore, 23/27, which is located on the PKA phosphorylation sites Ser23/24, showed that the major distribution was markedly narrowed, centered at 1.4?nm and 0.5?nm wide, accompanying the spin label immobilization of residue 27. Residues 35 and 69 at site 1 and 2 of cTnC exhibited partial immobilization of the attached spin labels upon complex formation. The results show that the extension exhibited a primarily partially folded or unfolded structure equilibrated with a transiently formed α-helix-like short structure over the length. We hypothesize that the structure binds at least near sites 1 and 2 of cTnC and that the specific secondary structure of the extension on cTnC becomes uncovered when decreasing the ionic strength demonstrating that only the phosphorylation regions of cTnI interact stereospecifically with cTnC.
机译：心肌肌钙蛋白I（CTNI）的N-延伸的二次结构通过测量附着于I和I和I的旋转标签之间的距离分布来确定4个残留物：15/19,23 / 27,27 / 31,35 / 39和43/47。这些区域的所有EPR光谱都被凸起，并且具有减少单旋转标记光谱的三分之二的幅度，并且由两个剩余距离分布相适合，主要分布一个展开从1到2.5？nm的范围和0.9≤nm的其他小峰。当在0.2μmKCl时延伸在CTNI-CTNC络合物中与CTNC结合时，才观察到轻微或没有明显的变化。然而，在0.1？M KCl，残留物43/47，位于延伸边界的PKC磷酸化位点Ser42 / 44处，专门表现出0.9ΩNM峰，如晶体结构中的α-螺旋从α-螺旋中所预期的复杂的。此外，位于PKA磷酸化位点Ser23 / 24上的23/27表明，主要分布显着变窄，以1.4Ω·Nm和0.5≤nm宽，伴随着残留物27的旋转标签固定。残留物35和在CTNC的现场1和2的Sitepitaply 1和2中表现出在复杂的形成上的附着的旋转标签的部分固定。结果表明，该延伸展示了主要部分折叠或展开的结构，其在该长度上具有瞬时形成的α-螺旋状短结构。我们假设该结构在CTNC的至少附近的位置1和2结合，并且在减少离子强度时，CTNC的延伸的延伸的特异性二次结构变得越来越覆盖，证明CTNI的磷酸化区域与CTNC相互作用。

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