DNA错配修复的“分子开关”控制

DNA错配修复系统识别并校正碱基错配以维持基因组稳定，是防止肿瘤发生的重要屏障。人体的错配修复基因缺陷会导致林奇综合症，携带者罹患结直肠癌、子宫内膜癌、卵巢癌和胃癌等疾病的风险远高于正常人群。近年来的研究揭示了E.coli错配修复的分子机制：MutS识别错配碱基后，将MutL招募到DNA上，随后MutL通过结合ATP形成clamp构象，将信号传递给下游元件以激活错配修复通路。然而，目前MutL的ATP水解活性在错配修复中的功能仍不明确，且人源MutL能否形成类似的clamp构象尚未有报道。本项目拟通过生物化学、遗传学和单分子成像等研究手段，阐明MutL及人源MLH1-PMS2是依赖ATP结合和水解的“分子开关”，并探索MLH1-PMS2作为“分子开关”在DNA错配修复中的功能。本研究将为进一步理解林奇综合症发病机理以及开发新型抗肿瘤药物靶点提供理论依据。

DNA mismatch repair system recognizes and corrects mispairs to maintain genome stability, preventing human from tumorigenesis. Defects in human mismatch repair genes cause Lynch Syndrome, the carriers of whom have much higher risks of colorectal cancer, endometrial cancer and ovarian cancer. Recent studies have revealed the molecular mechanism of E. coli DNA mismatch repair: After MutS recognizing the mispair, MutL is then recruited onto the DNA. The ATP binding of MutL induces a MutL clamp formation, which is responsible for downstream signaling to activate mismatch repair. However, it is still a mystery that how the MutL ATPase plays an important role in DNA mismatch repair. Furthermore, whether the human MutL homolog functions as a clamp remains unknown. Here we propose to examine the activity of MutL ATPase and the conformation of human MLH1-PMS2 by using biochemical and genetical approaches as well as single molecule imaging. We aim to show that both MutL and MLH1-PMS2 are “Molecular Switches” controlled by ATP binding and hydrolysis. We also plan to explore how MLH1-PMS2 transmit mismatch repair signal as a “Molecular Switch”, which will provide valuable basis for pharmaceutical and clinical application.