Hou Xi-Miao, Fu Yi-Ben, Wu Wen-Qiang, Wang Lei, Teng Fang-Yuan, Xie Ping, Wang Peng-Ye, Xi Xu-Guang
College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China.
Beijing National Laboratory for Condensed Matter Physics and CAS Key Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
Nucleic Acids Res. 2017 Nov 2;45(19):11401-11412. doi: 10.1093/nar/gkx766.
G-quadruplex (G4) can be formed by G-rich DNA sequences that are widely distributed throughout the human genome. Although G-triplex and G-hairpin have been proposed as G4 folding intermediates, their formation still requires further investigation by experiments. Here, we employed single-molecule FRET to characterize the folding dynamics of G4 from human telomeric sequence. First, we observed four states during G4 folding initially assigned to be anti-parallel G4, G-triplex, G-hairpin and unfolded ssDNA. Then we constructed putative intra-strand G-triplex, G-hairpin structures and confirmed their existences in both NaCl and KCl. Further studies revealed those structures are going through dynamic transitions between different states and show relatively weak dependence on cations, unlike G4. Based on those results and molecular dynamics simulations, we proposed a multi-pathway folding mechanism for human telomeric G4. The present work may shed new light on our current understanding about the existence and stability of G4 intermediate states.
富含鸟嘌呤的DNA序列可形成G-四链体（G4），这些序列广泛分布于人类基因组中。尽管有人提出G-三链体和G-发夹结构是G4折叠的中间体，但其形成仍需通过实验进一步研究。在此，我们采用单分子荧光共振能量转移技术来表征源自人类端粒序列的G4的折叠动力学。首先，我们在G4折叠过程中观察到四种状态，最初将它们分别确定为反平行G4、G-三链体、G-发夹结构和未折叠的单链DNA。然后，我们构建了假定的链内G-三链体和G-发夹结构，并证实它们在氯化钠和氯化钾中均存在。进一步的研究表明，与G4不同，这些结构在不同状态之间经历动态转变，并且对阳离子的依赖性相对较弱。基于这些结果和分子动力学模拟，我们提出了人类端粒G4的多途径折叠机制。本研究可能为我们目前对G4中间态的存在和稳定性的理解提供新的线索。
