Esposito G, Fogolari F, Damante G, Formisano S, Tell G, Leonardi A, Di Lauro R, Viglino P
Dipartimento di Scienze e Technologie Biomediche, Università degli Studi di Udine, Italy.
J Biomol NMR. 1997 Jun;9(4):397-407. doi: 10.1023/a:1018350611521.
The 1H NMR solution structure of the rat thyroid transcription factor 1 homeodomain (TTF-1 HD) showed that the molecule folds like classical homeodomains. The C-terminal extension of helix III (fragment 51-59) appeared to adopt a helical geometry, albeit not as rigid as the preceding portion, but the hydrogen-deuterium exchange of backbone amides and the NOE data provided evidence of a discontinuity between the two moieties of helix III at the highly conserved fragment Asn51-His52-Arg53. Analysis of quantitative measurements of isotope exchange rates allows one to recognize the general occurrence, in that region of HD motifs, of opposite effects to helix III stability. Asparagine, histidine and arginine residues occur most frequently at the beginning and end of protein helices. In TTF-1 HD a local fluctuation is observed in the fragment 51-53 which either kinks or tightens the alpha-helix. A search through the protein structure database reveals that the three most common variants of HD fragments 51-53 are often involved in helices and, frequently, in helix initiation or termination. For homeodomains in general, the nature of the fragment 51-53 may be related to the conformational dynamics of their DNA-recognition helix (helix III). Besides the specific results on fragment 51-53, the complete isotope exchange analysis of TTF-1 HD data shows that the partially solvent-exposed recognition helix is stabilized by hydrophobic interactions, like most of the structured regions of the molecule. Hydrophobic stabilization of the contacting regions meets the requirements of a DNA-interaction mechanism which, as shown with other DNA-protein complexes, should entail negative heat capacity variations due to changes in solvent exposure of the nonpolar protein surface.
大鼠甲状腺转录因子1同源结构域（TTF-1 HD）的1H NMR溶液结构表明，该分子折叠方式类似于经典同源结构域。螺旋III的C末端延伸部分（片段51 - 59）似乎呈现出螺旋几何结构，尽管不如前面部分那样刚性，但主链酰胺的氢氘交换和NOE数据表明，在高度保守的片段Asn51 - His52 - Arg53处，螺旋III的两个部分之间存在不连续性。对同位素交换率定量测量的分析使人们认识到，在HD基序的该区域普遍存在与螺旋III稳定性相反的作用。天冬酰胺、组氨酸和精氨酸残基最常出现在蛋白质螺旋的起始和末端。在TTF-1 HD中，在片段51 - 53处观察到局部波动，该波动使α螺旋发生扭结或收紧。在蛋白质结构数据库中进行搜索发现，HD片段51 - 53的三种最常见变体经常参与螺旋结构，并且频繁地参与螺旋起始或终止。一般来说，对于同源结构域，片段51 - 53的性质可能与其DNA识别螺旋（螺旋III）的构象动力学有关。除了关于片段51 - 53的具体结果外，TTF-1 HD数据的完整同位素交换分析表明，部分暴露于溶剂中的识别螺旋通过疏水相互作用得以稳定，这与该分子的大多数结构化区域类似。接触区域的疏水稳定作用符合DNA相互作用机制的要求，正如其他DNA - 蛋白质复合物所显示的那样，由于非极性蛋白质表面溶剂暴露的变化，这应该会导致负的热容变化。
