Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry , Beijing Normal University , Beijing 100875 , China.
J Phys Chem B. 2019 Jul 5;123(26):5405-5411. doi: 10.1021/acs.jpcb.9b02823. Epub 2019 Jun 20.
DNA G-quadruplex (G4) could adopt multiple conformations, and the exact conformation is related to the presence of cations. However, the fact that cations with various concentrations could competitively bind with G4 is rarely investigated, which greatly limits the potential applications of G4-based sensors. Here, with PW17 (a G4-forming DNA sequence) as an example, Na and K with different concentrations competitively binding with PW17 are clarified by circular dichroism spectroscopy and electrospray ionization mass spectroscopy. Although Na could induce PW17 switching to unstable and antiparallel Na-stabilized PW17 (2Na-PW17) ( C = 5-70 mM) and further to stable and hybrid 2Na-PW17 ( C = 70-800 mM), K ( C = 0.1-10 mM) could replace Na in 2Na-PW17 with 2Na-PW17 transforming into K-stabilized PW17 (2K-PW17). Moreover, the replacing ability strictly relied on C and C. In the switching process, a stable intermediate including a K and an Na in one G4 (K-Na-PW17) is firstly detected. Importantly, the stable K-Na-PW17 is detected at 0.5 mM K and 140 mM Na. Based on the facts, the interferences of Na with the performance of PW17-based K sensors are investigated. With the stable K-Na-PW17 as a sensing probe and protoporphyrin IX (PPIX) as a G4 fluorescent read-out probe, a linear relationship between C (500 nM-10 mM) and PPIX fluorescence is observed, which provides a fluorescence assay for detecting K with the co-existing 140 mM Na. This study exhibits clear evidence of Na and K competitively binding with G4 and finds a novel and stable K-Na-PW17, which provides a clue to further explore G4 functions in Na-contained samples.
DNA 四链体 (G4) 可以采取多种构象，而确切的构象与阳离子的存在有关。然而，目前很少有研究探讨具有不同浓度的阳离子如何与 G4 竞争结合，这极大地限制了基于 G4 的传感器的潜在应用。在这里，以 PW17（一种形成 G4 的 DNA 序列）为例，通过圆二色光谱和电喷雾电离质谱阐明了不同浓度的 Na 和 K 与 PW17 的竞争结合。虽然 Na 可以诱导 PW17 向不稳定的反平行 Na 稳定的 PW17（2Na-PW17）（C = 5-70 mM）转变，并进一步向稳定的杂交 2Na-PW17（C = 70-800 mM）转变，但 K（C = 0.1-10 mM）可以在 2Na-PW17 中取代 Na，使 2Na-PW17 转变为 K 稳定的 PW17（2K-PW17）。此外，取代能力严格依赖于 C 和 C。在转换过程中，首先检测到一种包含一个 G4 中的 K 和一个 Na 的稳定中间体（K-Na-PW17）。重要的是，在 0.5 mM K 和 140 mM Na 时检测到稳定的 K-Na-PW17。基于这些事实，研究了 Na 对基于 PW17 的 K 传感器性能的干扰。使用稳定的 K-Na-PW17 作为传感探针和原卟啉 IX（PPIX）作为 G4 荧光读出探针，观察到 C（500 nM-10 mM）和 PPIX 荧光之间的线性关系，这为在共存 140 mM Na 的情况下检测 K 提供了一种荧光分析方法。本研究提供了 Na 和 K 与 G4 竞争结合的明确证据，并发现了一种新型稳定的 K-Na-PW17，为进一步探索 G4 在含 Na 样品中的功能提供了线索。
