在富含鸟嘌呤的人端粒和癌基因启动子中形成的DNAG-四链体二级结构在功能上很重要,并已成为有希望的新型癌症特异性药物靶标。这些球状分子内结构被K+或Na+稳定,并且在生理溶液条件下容易形成。此外,G-四链体是表观遗传特征,可以与相互作用的蛋白质一起改变染色质的结构和功能。这里,我们讨论了我们在过去二十年中的努力,以了解在关键癌基因启动子和人类端粒中形成的DNAG-四链体的结构和功能,以及它们与小分子的相互作用。使用高场核磁共振光谱,我们确定了K溶液中生理相关的端粒G-四链体的高分辨率结构,主要形式(杂交-2)和次要形式(杂交-1),以及两四分体中间体。端粒DNA的内在结构多态性可能对人类端粒的生物学具有重要意义。我们提出了一个相互转换的模型。最近,我们研究了MYC的G-四链体,BCL2,PDGFR-β,VEGF,和k-RAS癌基因启动子。我们确定了在MYC启动子中形成的主要G-四链体的结构,并行G-四链体的原型。这是具有1-nt环的平行链G3NG3结构基序的第一个例子,在启动子序列中普遍存在,并且可能在进化上被选择来启动折叠。值得注意的是,平行的MYC启动子G-四链体是高度稳定的。此外,我们确定了人BCL2,VEGF,和PDGFR-β启动子,每个都采用独特的结构。例如,BCL2启动子在两个相邻区域含有不同的可互换的G-四链体,表明不同蛋白质的精确调节。PDGFR-β启动子采用独特的“断链”和空位G-四链体,它可以被细胞鸟嘌呤代谢物识别为潜在的调节作用。与小分子复合物中G-四链体的结构信息对于理解特定识别和基于结构的合理药物设计至关重要。我们的研究表明,许多G-四链体具有独特的结构特征,如封盖和环结构,允许药物和蛋白质的特异性识别。这代表了将DNA理解为药物靶标的范式转变:而不是统一的,双链DNA中的非选择性结合位点,G-四链体被视为一类新型的选择性靶向药物受体。我们专注于用小分子靶向生物相关的MYC启动子G-四链体(MycG4),并确定了其第一个和其他药物复合物结构。最近,我们发现经临床试验的茚并异喹啉可作为强MycG4结合剂和有效的MYC抑制剂.我们还发现了靶向在PDGFR-β启动子中形成的独特的dGMP结合的vG4的药物。此外,我们确定了第一个小分子的复杂结构,这些小分子特异性识别生理相关的人类端粒G-四链体。与先前公认的最佳G-四链体配体是大的芳族或环状化合物的教条不同,我们的结果表明,具有适当官能团的较小的不对称化合物是特异性结合G-四链体的更好选择.这项工作为未来旨在了解G-四链体的细胞功能和G-四链体靶向药物设计的工作奠定了坚实的基础。
DNA G-quadruplex secondary structures formed in guanine-rich human telomeres and oncogene promoters are functionally important and have emerged as a promising new class of cancer-specific drug targets. These globular intramolecular structures are stabilized by K+ or Na+ and form readily under physiological solution conditions. Moreover, G-quadruplexes are epigenetic features and can alter chromatin structure and function together with interactive proteins. Here, we discuss our efforts over the last two decades to understand the structures and functions of DNA G-quadruplexes formed in key oncogene promoters and human telomeres and their interactions with small molecules. Using high-field NMR spectroscopy, we determined the high-resolution structures of physiologically relevant telomeric G-quadruplexes in K+ solution with a major form (hybrid-2) and a minor form (hybrid-1), as well as a two-tetrad intermediate. The intrinsic structural polymorphism of telomeric DNA may be important for the biology of human telomeres, and we proposed a model for the interconversion. More recently, we have worked on G-quadruplexes of MYC, BCL2, PDGFR-β, VEGF, and k-RAS oncogene promoters. We determined the structure of the major G-quadruplex formed in the MYC promoter, a prototype for parallel G-quadruplexes. It is the first example of the parallel-stranded G3NG3 structure motif with a 1-nt loop, which is prevalent in promoter sequences and likely evolutionarily selected to initiate folding. Remarkably, the parallel MYC promoter G-quadruplexes are highly stable. Additionally, we determined the molecular structures of G-quadruplexes formed in human BCL2, VEGF, and PDGFR-β promoters, each adopting a unique structure. For example, the BCL2 promoter contains distinct interchangeable G-quadruplexes in two adjacent regions, suggesting precise regulation by different proteins. The PDGFR-β promoter adopts unique \"broken-strand\" and vacancy G-quadruplexes, which can be recognized by cellular guanine metabolites for a potential regulatory role.Structural information on G-quadruplexes in complex with small-molecules is critical for understanding specific recognition and structure-based rational drug design. Our studies show that many G-quadruplexes contain unique structural features such as capping and loop structures, allowing specific recognition by drugs and protein. This represents a paradigm shift in understanding DNA as a drug target: Rather than a uniform, nonselective binding site in duplex DNA, the G-quadruplex is being pursued as a new class of selectively targetable drug receptors. We focus on targeting the biologically relevant MYC promoter G-quadruplex (MycG4) with small molecules and have determined its first and additional drug complex structures. Very recently, we have discovered clinically tested indenoisoquinolines as strong MycG4 binders and potent MYC inhibitors. We have also discovered drugs targeting the unique dGMP-bound-vG4 formed in the PDGFR-β promoter. Moreover, we determined the complex structures of the first small molecules that specifically recognize the physiologically relevant human telomeric G-quadruplexes. Unlike the previously recognized dogma that the optimal G-quadruplex ligands are large aromatic or cyclic compounds, our results suggest that smaller asymmetric compounds with appropriate functional groups are better choices to specifically bind G-quadruplexes. This body of work lays a strong foundation for future work aimed at understanding the cellular functions of G-quadruplexes and G-quadruplex-targeted drug design.