The basic helix–loop–helix leucine zipper (bHLH-LZ) transcription factor (TF) MYC is in large part an intrinsically disordered oncoprotein. In complex with its obligate heterodimerization partner MAX, MYC preferentially binds E-Box DNA sequences (CANNTG). At promoters containing these sequence motifs, MYC controls fundamental cellular processes such as cell cycle progression, metabolism, and apoptosis. A vast network of proteins in turn regulates MYC function via intermolecular interactions. In this work, we establish another layer of MYC regulation by intramolecular interactions. We used nuclear magnetic resonance (NMR) spectroscopy to identify and map multiple binding sites for the C-terminal MYC:MAX DNA-binding domain (DBD) on the intrinsically disordered regions (IDRs) in the MYC N-terminus. We find that these binding events in trans are driven by electrostatic attraction, that they have distinct affinities, and that they are competitive with DNA binding. Thereby, we observe the strongest effects for the N-terminal MYC box 0 (Mb0), a conserved motif involved in MYC transactivation and target gene induction. We prepared recombinant full-length MYC:MAX complex and demonstrate that the interactions identified in this work are also relevant in cis, i.e., as intramolecular interactions. These findings are supported by surface plasmon resonance (SPR) experiments, which revealed that intramolecular IDR:DBD interactions in MYC decelerate the association of MYC:MAX complexes to DNA. Our work offers new insights into how bHLH-LZ TFs are regulated by intramolecular interactions, which open up new possibilities for drug discovery.

中文翻译：

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转录因子 MYC:MAX 中本质上无序的区域通过分子内相互作用调节 DNA 结合

基本螺旋-环-螺旋亮氨酸拉链 (bHLH-LZ) 转录因子 (TF) MYC 在很大程度上是一种本质上无序的癌蛋白。与其专性异二聚化伙伴 MAX 复合时，MYC 优先结合 E-Box DNA 序列 (CANNTG)。在包含这些序列基序的启动子处，MYC 控制基本的细胞过程，例如细胞周期进程、代谢和细胞凋亡。庞大的蛋白质网络反过来通过分子间相互作用调节 MYC 功能。在这项工作中，我们通过分子内相互作用建立了 MYC 调节的另一层。我们使用核磁共振 (NMR) 光谱来识别和绘制 MYC N 端固有无序区域 (IDR) 上 C 端 MYC:MAX DNA 结合域 (DBD) 的多个结合位点。我们发现这些反式结合事件是由静电引力驱动的，它们具有不同的亲和力，并且它们与 DNA 结合具有竞争性。因此，我们观察到 N 端 MYC box 0 (Mb0) 的最强效应，这是一个参与 MYC 反式激活和靶基因诱导的保守基序。我们制备了重组全长 MYC:MAX 复合物，并证明本工作中确定的相互作用也与顺式相关，即作为分子内相互作用。这些发现得到了表面等离子共振 (SPR) 实验的支持，该实验揭示了 MYC 中分子内 IDR:DBD 相互作用减缓了 MYC:MAX 复合物与 DNA 的结合。我们的工作提供了关于 bHLH-LZ TF 如何通过分子内相互作用调节的新见解，这为药物发现开辟了新的可能性。