School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, 430030 Wuhan, China.
CAS Key Laboratory of Magnetic Resonance in Biological Systems, State Key Laboratory of Magnetic Resonance and Atomic Molecular Physics, National Center for Magnetic Resonance at Wuhan, Wuhan Institute of Physics and Mathematics of the Chinese Academy of Sciences, 430071 Wuhan, China.
J Phys Chem Lett. 2020 Oct 1;11(19):7966-7971. doi: 10.1021/acs.jpclett.0c02229. Epub 2020 Sep 10.
Guanine-rich repeat sequences are known to adopt diverse G-quadruplex (G4) topologies. Determining the unfolding rates of individual G4 species is challenging due to the coexistence of multiple G4 conformations in a solution. Here, using single-molecule magnetic tweezers, we systematically measured the unfolding force distributions of 4 oncogene promoter G4s, 12 model sequences with two 1-nucleotide (nt) thymine loops that predominantly adopt parallel-stranded G4 structures, and 6 sequences forming multiple G4 structures. All parallel-stranded G4s reveal an unfolding force peak at 40-60 pN, which is associated with extremely slow unfolding rates on the order of 10-10 s. In contrast, nonparallel G4s and partially folded intermediate states reveal an unfolding force peak <40 pN. These results suggest a strong correlation between the parallel-stranded G4s folding topology and the slow unfolding rates and provide important insights into the mechanism that govern the stability and the transition kinetics of G4s.
富含鸟嘌呤的重复序列已知会采用多种 G-四链体 (G4) 拓扑结构。由于在溶液中存在多种 G4 构象，因此确定单个 G4 物种的展开速率具有挑战性。在这里，我们使用单分子磁镊系统地测量了 4 个癌基因启动子 G4、12 个具有两个 1-核苷酸 (nt) 胸腺嘧啶环的模型序列（主要采用平行链 G4 结构）和 6 个形成多个 G4 结构的序列的展开力分布。所有平行链 G4 均在 40-60 pN 处显示出展开力峰值，这与 10-10 s 数量级的极慢展开速率相关。相比之下，非平行 G4 和部分折叠的中间态在 <40 pN 处显示展开力峰值。这些结果表明平行链 G4 折叠拓扑结构与缓慢展开速率之间存在很强的相关性，并为控制 G4 稳定性和跃迁动力学的机制提供了重要的见解。
