College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China.
Université Lyon, ENS de Lyon, Université Claude Bernard, CNRS UMR 5239, INSERM U1210, LBMC, 46 allée d'Italie Site Jacques Monod, 69007, Lyon, France.
Structure. 2018 Mar 6;26(3):403-415.e4. doi: 10.1016/j.str.2018.01.008. Epub 2018 Feb 8.
Helicase DHX36 plays essential roles in cell development and differentiation at least partially by resolving G-quadruplex (G4) structures. Here we report crystal structures of the Drosophila homolog of DHX36 (DmDHX36) in complex with RNA and a series of DNAs. By combining structural, small-angle X-ray scattering, molecular dynamics simulation, and single-molecule fluorescence studies, we revealed that positively charged amino acids in RecA2 and OB-like domains constitute an elaborate structural pocket at the nucleic acid entrance, in which negatively charged G4 DNA is tightly bound and partially destabilized. The G4 DNA is then completely unfolded through the 3'-5' translocation activity of the helicase. Furthermore, crystal structures and DNA binding assays show that G-rich DNA is preferentially recognized and in the presence of ATP, specifically bound by DmDHX36, which may cooperatively enhance the G-rich DNA translocation and G4 unfolding. On the basis of these results, a conceptual G4 DNA-resolving mechanism is proposed.
解旋酶 DHX36 通过解开 G-四链体（G4）结构，至少在一定程度上发挥着细胞发育和分化的重要作用。在这里，我们报告了与 RNA 以及一系列 DNA 复合物的果蝇 DHX36 同源物（DmDHX36）的晶体结构。通过结合结构、小角 X 射线散射、分子动力学模拟和单分子荧光研究，我们揭示了 RecA2 和 OB 样结构域中的正电荷氨基酸在核酸入口处构成了一个精细的结构口袋，其中带负电荷的 G4 DNA 被紧密结合并部分失稳。然后，G4 DNA 通过解旋酶的 3′-5′移位活性被完全展开。此外，晶体结构和 DNA 结合实验表明，富含 G 的 DNA 被优先识别，并且在 ATP 的存在下，DmDHX36 特异性结合，这可能协同增强富含 G 的 DNA 易位和 G4 展开。基于这些结果，提出了一个概念性的 G4 DNA 解析机制。
