Dynamic control of strand excision during human DNA mismatch repair
Dynamic control of strand excision during human DNA mismatch repair
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DOI：
10.1073/pnas.1523748113
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发表时间：
2016-03-22
影响因子：
11.1
通讯作者：
Lee, Jong-Bong
中科院分区：
文献类型：
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作者：
Jeon, Yongmoon;Kim, Daehyung;Lee, Jong-Bong
错配修复（MMR）由进化上保守的MutS同源物（MSH）和MutL同源物（MLH/PMS）激活。MSH识别错配的核苷酸并形成非常稳定的滑动夹，其可以被MLH/PMS结合以最终授权从远端3 '-或5'-DNA断裂开始的链特异性切除。与完整MMR反应相关的机械过程仍然是个谜。纯化的人（智人或Hs）5 '-MMR切除反应需要HsMSH 2-HsMSH 6异源二聚体、5' -> 3'核酸外切酶HsEXOI和单链结合异源三聚体HsRPA。HsMLH 1-HsPMS 2异二聚体显著影响细胞提取物中的5 ′-MMR切除，但在纯化的系统中不需要。使用实时单分子成像，我们表明，HsRPA或大肠杆菌EcSSB限制HsEXOI切除活性的切口或缺口的DNA。HsMSH 2-HsMSH 6通过克服HsRPA/EcSSB抑制来激活HsEXOI，并利用多个动态滑动夹来增加束长度。相反，HsMLH 1-HsPMS 2通过控制切除复合物的数量来调节束长度，提供与5' MMR的连接。
Mismatch repair (MMR) is activated by evolutionarily conserved MutS homologs (MSH) and MutL homologs (MLH/PMS). MSH recognizes mismatched nucleotides and form extremely stable sliding clamps that may be bound by MLH/PMS to ultimately authorize strand-specific excision starting at a distant 3'- or 5'-DNA scission. The mechanical processes associated with a complete MMR reaction remain enigmatic. The purified human (Homo sapien or Hs) 5'-MMR excision reaction requires the HsMSH2-HsMSH6 heterodimer, the 5' -> 3' exonuclease HsEXOI, and the single-stranded binding heterotrimer HsRPA. The HsMLH1-HsPMS2 heterodimer substantially influences 5'-MMR excision in cell extracts but is not required in the purified system. Using real-time single-molecule imaging, we show that HsRPA or Escherichia coli EcSSB restricts HsEXOI excision activity on nicked or gapped DNA. HsMSH2-HsMSH6 activates HsEXOI by overcoming HsRPA/EcSSB inhibition and exploits multiple dynamic sliding clamps to increase tract length. Conversely, HsMLH1-HsPMS2 regulates tract length by controlling the number of excision complexes, providing a link to 5' MMR.