Pavlova Anzhela V, Monakhova Mayya V, Ogloblina Anna M, Andreeva Natalia A, Laptev Gennady Yu, Polshakov Vladimir I, Gromova Elizaveta S, Zvereva Maria I, Yakubovskaya Marianna G, Oretskaya Tatiana S, Kubareva Elena A, Dolinnaya Nina G
Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1, 119991 Moscow, Russia.
Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory 1, 119991 Moscow, Russia.
Int J Mol Sci. 2020 Nov 20;21(22):8773. doi: 10.3390/ijms21228773.
DNA mismatch repair (MMR) plays a crucial role in the maintenance of genomic stability. The main MMR protein, MutS, was recently shown to recognize the G-quadruplex (G4) DNA structures, which, along with regulatory functions, have a negative impact on genome integrity. Here, we studied the effect of G4 on the DNA-binding activity of MutS from (methyl-independent MMR) in comparison with MutS from (methyl-directed MMR) and evaluated the influence of a G4 on the functioning of other proteins involved in the initial steps of MMR. For this purpose, a new DNA construct was designed containing a biologically relevant intramolecular stable G4 structure flanked by double-stranded regions with the set of DNA sites required for MMR initiation. The secondary structure of this model was examined using NMR spectroscopy, chemical probing, fluorescent indicators, circular dichroism, and UV spectroscopy. The results unambiguously showed that the d(GGGT) motif, when embedded in a double-stranded context, adopts a G4 structure of a parallel topology. Despite strong binding affinities of MutS and MutL for a G4, the latter is not recognized by MMR as a signal for repair, but does not prevent MMR processing when a G4 and G/T mismatch are in close proximity.
DNA错配修复（MMR）在维持基因组稳定性方面发挥着关键作用。主要的MMR蛋白MutS最近被证明能够识别G-四链体（G4）DNA结构，该结构除了具有调控功能外，还会对基因组完整性产生负面影响。在这里，我们研究了G4对来自[甲基独立MMR]的MutS的DNA结合活性的影响，并与来自[甲基定向MMR]的MutS进行了比较，同时评估了G4对参与MMR初始步骤的其他蛋白质功能的影响。为此，设计了一种新的DNA构建体，其包含一个具有生物学相关性的分子内稳定G4结构，两侧是双链区域，并带有MMR起始所需的一组DNA位点。使用核磁共振光谱、化学探针、荧光指示剂、圆二色性和紫外光谱对该模型的二级结构进行了检测。结果明确表明，d（GGGT）基序在双链环境中时会形成平行拓扑结构的G4结构。尽管MutS和MutL对G4具有很强的结合亲和力，但G4不会被[甲基独立MMR]识别为修复信号，不过当G4和G/T错配紧邻时，它不会阻止MMR的进行。
