2012年7月5日，北京生命科学研究所杜立林实验室在《PLoS Genetics》在线发表题为“Phosphorylation-Dependent Interactions between Crb2 and Chk1 Are Essential for DNA Damage Checkpoint”的文章。
为确保基因组的稳定性，真核细胞中存在一套监控DNA完整性并传递DNA损伤信号的系统，称为 DNA损伤检验点通路。参与该信号传导通路的蛋白包括识别DNA损伤的感应蛋白，下游的效应激酶，还有介导感应蛋白与效应激酶间信号传导的中介蛋白。Chk1是最重要的效应激酶之一，在真核生物中高度保守。在模式生物裂殖酵母中，中介蛋白Crb2对效应激酶Chk1的激活至关重要，但是Crb2参与激活Chk1的分子机理却并不清楚。本论文对这一问题进行了研究，发现Crb2上的两个磷酸化位点（T73和S80）对于Chk1在DNA损伤部位的聚集和Chk1的激活是必需的。一个包含这两个磷酸化位点的19个氨基酸的肽段可以在体外与Chk1直接结合。通过将这一肽段定位在DNA损伤部位，本论文证明了Crb2和另一个中介蛋白复合体Rad9-Rad1-Hus1 (9-1-1)的主要作用是将Chk1募集到DNA损伤部位。
本研究工作主要由我所博士生曲萌完成。其他作者包括我所的董梦秋博士，董梦秋实验室的博士生杨兵和陶莉，以及美国Scripps研究所的Paul Russell博士和John R. Yates III博士。杜立林博士为本文的通讯作者。此项研究由科技部和北京市政府资助。（生物谷Bioon.com）
doi:10.1371/journal.pgen.1002817
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Phosphorylation-Dependent Interactions between Crb2 and Chk1 Are Essential for DNA Damage Checkpoint
Meng Qu1,2, Bing Yang2, Li Tao2, John R. Yates III3, Paul Russell4, Meng-Qiu Dong2, Li-Lin Du2*
In response to DNA damage, the eukaryotic genome surveillance system activates a checkpoint kinase cascade. In the fission yeast Schizosaccharomyces pombe, checkpoint protein Crb2 is essential for DNA damage-induced activation of downstream effector kinase Chk1. The mechanism by which Crb2 mediates Chk1 activation is unknown. Here, we show that Crb2 recruits Chk1 to double-strand breaks (DSBs) through a direct physical interaction. A pair of conserved SQ/TQ motifs in Crb2, which are consensus phosphorylation sites of upstream kinase Rad3, is required for Chk1 recruitment and activation. Mutating both of these motifs renders Crb2 defective in activating Chk1. Tethering Crb2 and Chk1 together can rescue the SQ/TQ mutations, suggesting that the main function of these phosphorylation sites is promoting interactions between Crb2 and Chk1. A 19-amino-acid peptide containing these SQ/TQ motifs is sufficient for Chk1 binding in vitro when one of the motifs is phosphorylated. Remarkably, the same peptide, when tethered to DSBs by fusing with either recombination protein Rad22/Rad52 or multi-functional scaffolding protein Rad4/Cut5, can rescue the checkpoint defect of crb2Δ. The Rad22 fusion can even bypass the need for Rad9-Rad1-Hus1 (9-1-1) complex in checkpoint activation. These results suggest that the main role of Crb2 and 9-1-1 in DNA damage checkpoint signaling is recruiting Chk1 to sites of DNA lesions.
