Hibino Emi, Inoue Rintaro, Sugiyama Masaaki, Kuwahara Jun, Matsuzaki Katsumi, Hoshino Masaru
Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto, Sakyo-ku, 606-8501, Japan.
Research Reactor Institute, Kyoto University, Sennan-gun, Osaka, 590-0494, Japan.
Protein Sci. 2017 Nov;26(11):2280-2290. doi: 10.1002/pro.3287. Epub 2017 Sep 27.
The expression of eukaryotic genes is precisely controlled by interactions between general transcriptional factors and promoter-specific transcriptional activators. The fourth element of TATA-box binding protein-associated factor (TAF4), an essential subunit of the general transcription factor TFIID, serves as a coactivator for various promoter-specific transcriptional regulators. Interactions between TAF4 and site-specific transcriptional activators, such as Sp1, are important for regulating the expression levels of genes of interest. However, only limited information is available on the molecular mechanisms underlying the interactions between these transcriptional regulatory proteins. We herein analyzed the interaction between the transcriptional factors Sp1 and TAF4 using high-resolution solution nuclear magnetic resonance spectroscopy. We found that four glutamine-rich (Q-rich) regions in TAF4 were largely disordered under nearly physiological conditions. Among them, the first Q-rich region in TAF4 was essential for the interaction with another Q-rich region in the Sp1 molecule, most of which was largely disordered. The residues responsible for this interaction were specific and highly localized in a defined region within a range of 20-30 residues. Nevertheless, a detailed analysis of C-chemical shift values suggested that no significant conformational change occurred upon binding. These results indicate a prominent and exceptional binding mode for intrinsically disordered proteins other than the well-accepted concept of "coupled folding and binding."
真核基因的表达由通用转录因子和启动子特异性转录激活因子之间的相互作用精确控制。TATA盒结合蛋白相关因子（TAF4）是通用转录因子TFIID的一个必需亚基，其第四个元件作为各种启动子特异性转录调节因子的共激活因子。TAF4与位点特异性转录激活因子（如Sp1）之间的相互作用对于调节感兴趣基因的表达水平很重要。然而，关于这些转录调节蛋白之间相互作用的分子机制，目前仅有有限的信息。我们在此使用高分辨率溶液核磁共振光谱分析了转录因子Sp1和TAF4之间的相互作用。我们发现，在接近生理条件下，TAF4中的四个富含谷氨酰胺（Q-rich）区域在很大程度上是无序的。其中，TAF4中的第一个富含谷氨酰胺区域对于与Sp1分子中的另一个富含谷氨酰胺区域相互作用至关重要，后者大部分也是无序的。负责这种相互作用的残基是特异性的，并且高度局限于20 - 30个残基范围内的一个特定区域。然而，对C化学位移值的详细分析表明，结合后没有发生显著的构象变化。这些结果表明，除了广为接受的“耦合折叠与结合”概念之外，内在无序蛋白存在一种显著且特殊的结合模式。
