SETD3甲基化修饰MCM复合体调控DNA复制的分子机制

组氨酸甲基化修饰是生物体中普遍存在的蛋白质翻译后修饰方式之一，但对其生物学功能知之甚少。有研究发现，甲基转移酶SETD3可以修饰β-Actin蛋白第73位上的组氨酸，增强肌动蛋白的多聚化能力，促进子宫平滑肌收缩和避免原发性难产，首次揭示了该修饰在高等生物中的功能。我们的前期结果表明，SETD3是一个细胞周期调控蛋白，可以通过依赖其酶活的方式参与调控细胞周期进程和DNA复制。机制方面，申请人发现SETD3与MCM复合物结合，可以甲基化修饰MCM7上的组氨酸，暗示其可能在DNA复制中发挥作用。本项目拟利用细胞生物学、生物化学、新生DNA链高通量测序及生物信息学分析等多种手段，探究SETD3甲基化修饰MCM复合体调控DNA复制的分子机制。本项目旨在深入理解DNA复制进程的调控机制，阐明组氨酸甲基化修饰新的生物学功能。项目的实施将对于探究与DNA复制相关的人类疾病发生机理奠定基础。

Histidine methylation is one of the prevalent protein post-translational modifications in diverse organisms. However, its biological functions are still enigmatic. Recently, several studies have identified SETD3 as the first known metazoan histidine methyltransferase and the enzyme responsible for methylating beta-Actin on histidine 73 (H73me). Interestingly, H73me modestly accelerates actin filament assembly, and promotes contraction of uterine smooth muscle，thereby preventing primary dystocia. This finding uncovers a pivotal role of histidine methylation in higher eukaryotes. Our previous results showed that SETD3 level is fluctuated during cell-cycle progression with the highest expression level at S phase, suggesting the involvement of SETD3 in DNA replication. Our preliminary data further verified that SETD3 regulates DNA replication during S phase in an enzymatic-dependent manner. By an efficient proximity biotinylation-dependent labelling technique combined with mass spectrum analysis, we identified that SETD3 directly interacts with the MCM complex that is a core machinery for DNA replication process. Mechanistically, we found that SETD3 could methylate histidine residues on MCM7 protein, a subunit of the MCM complex. In this proposal, using multiple approaches including cell biology, biochemistry, nascent DNA high-through sequencing, and bioinformatic analysis, we aim to elucidate the molecular mechanism underlying DNA replication regulated by the SETD3 methyltransferase. This project would be of great significance for understanding the elaborate molecular basis of DNA replication event, as well as expanding the novel biological functions of histidine methylation, which may provide insights on the onset of DNA replication-related human diseases.