Lee Sungjin, Kim Jinwoo, Han Suyeong, Park Chin-Ju
Department of Chemistry, Gwangju Institute of Science and Technology, Gwangju 61005, Korea.
ACS Omega. 2020 Jun 11;5(24):14513-14522. doi: 10.1021/acsomega.0c01176. eCollection 2020 Jun 23.
G-quadruplex (G4) is a noncanonical DNA secondary structure formed by Hoogsteen base pairing. It is recognized by various DNA helicases involved in DNA metabolism processes such as replication and transcription. Human Bloom syndrome protein (BLM), one of five human RecQ helicases, is a G4 helicase. While several studies revealed the mechanism of G4 binding and unfolding by the conserved RecQ C-terminal (RQC) domain of BLM, how RQC recognizes different G4 topologies is still unclear. Here, we investigated the interaction of Myc-22(14/23T) G4 from the c-Myc promoter and hTelo G4 from the telomeric sequence with RQC. Myc-22(14/23T) and hTelo form parallel and (3+1) hybrid topologies, respectively. Our circular dichroism (CD) spectroscopy data indicate that RQC can partially unfold the parallel G4, even with a short 3' overhang, while it can only partially unfold the (3+1) hybrid G4 with a 3' overhang of 6 nucleotides or longer. We found that the intrinsic thermal stability of G4 does not determine RQC-induced G4 unfolding by comparing of G4s. We also showed that both parallel and (3+1) hybrid G4s bind to the β-wing region of RQC. Thermodynamic analysis using isothermal titration calorimetry (ITC) showed that all interactions were endothermic and entropically driven. We suggest that RQC partially unfolds the parallel G4 more efficiently than the (3+1) hybrid G4 and binds to various G4 structures using its β-wing region. By this information, our research provides new insights into the influence of G4 structure on DNA metabolic processes involving BLM.
G-四链体（G4）是一种由Hoogsteen碱基配对形成的非经典DNA二级结构。它被参与DNA代谢过程（如复制和转录）的各种DNA解旋酶所识别。人类布鲁姆综合征蛋白（BLM）是人类五种RecQ解旋酶之一，是一种G4解旋酶。虽然多项研究揭示了BLM保守的RecQ C末端（RQC）结构域结合和展开G4的机制，但RQC如何识别不同的G4拓扑结构仍不清楚。在这里，我们研究了来自c-Myc启动子的Myc-22(14/23T) G4和来自端粒序列的hTelo G4与RQC的相互作用。Myc-22(14/23T)和hTelo分别形成平行拓扑结构和（3+1）杂合拓扑结构。我们的圆二色性（CD）光谱数据表明，即使有短的3'突出端，RQC也能部分展开平行G4，而只有当3'突出端为6个核苷酸或更长时，它才能部分展开（3+1）杂合G4。通过比较不同G4的 ，我们发现G4的固有热稳定性并不能决定RQC诱导的G4展开。我们还表明，平行G4和（3+1）杂合G4都与RQC的β-翼区域结合。使用等温滴定量热法（ITC）进行热力学分析表明，所有相互作用都是吸热的且由熵驱动。我们认为，RQC比（3+1）杂合G4更有效地部分展开平行G4，并利用其β-翼区域结合各种G4结构。基于这些信息，我们的研究为G4结构对涉及BLM的DNA代谢过程的影响提供了新的见解。
