Structural basis for DNA recognition and nuclease processing by the Mre11 homologue SbcD in double-strand breaks repair
Structural basis for DNA recognition and nuclease processing by the Mre11 homologue SbcD in double-strand breaks repair
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Mre11 同源物 SbcD 在双链断裂修复中进行 DNA 识别和核酸酶加工的结构基础。
DOI：
10.1107/s139900471302693x
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发表时间：
2014-02-01
影响因子：
2.2
通讯作者：
Liang, Dong-cai
中科院分区：
文献类型：
--
作者：
Liu, Shun;Tian, Li-fei;Liang, Dong-cai
由减数分裂重组11 （Mre11）、Rad50和奈亨断裂综合征1 （Nbs1）组成的Mre11复合体在DNA双链断裂（DSBs）的感知、加工和修复中发挥着多种重要作用。本文报道了大肠杆菌Mre11同源物SbcD及其Mn2+配合物的晶体结构。SbcD的二聚化依赖于两种单体的α2、α3、α2′和α3′螺旋组成的四螺旋束，而SbcD二聚体中α3′和α3′螺旋的不规则和弯曲构象导致其二聚体的排列与先前报道的Mre11二聚体不同。这一发现表明在DNA底物识别中具有明显的选择性。生化数据结合晶体结构表明，在高浓度Mn2+的作用下，SbcD单体表现出单链DNA （ssDNA）内切酶活性和双链DNA （dsDNA）外切酶活性。首次使用原子力显微镜分析证明了SbcD单体也具有Mn2+依赖的dsDNA内切酶活性。SbcD的环β7-α6可能是分子开关，在调节底物结合、催化反应和状态转变中起重要作用。在结构和突变分析的基础上，提出了一种新的SbcD的ssdna结合模型，为Mre11复合物对DSBs修复的催化机制提供了新的见解。
The Mre11 complex comprising meiotic recombination 11 (Mre11), Rad50 and Nijmegen breakage syndrome 1 (Nbs1) plays multiple important roles in the sensing, processing and repair of DNA double-strand breaks (DSBs). Here, crystal structures of the Escherichia coli Mre11 homologue SbcD and its Mn2+ complex are reported. Dimerization of SbcD depends on a four-helix bundle consisting of helices α2, α3, α2' and α3' of the two monomers, and the irregular and bent conformation of helices α3 and α3' in the SbcD dimer results in a dimeric arrangement that differs from those of previously reported Mre11 dimers. This finding indicates a distinct selectivity in DNA substrate recognition. The biochemical data combined with the crystal structures revealed that the SbcD monomer exhibits single-stranded DNA (ssDNA) endonuclease activity and double-stranded DNA (dsDNA) exonuclease activity on the addition of a high concentration of Mn2+. For the first time, atomic force microscopy analysis has been used to demonstrate that the SbcD monomer also possesses Mn2+-dependent dsDNA endonuclease activity. Loop β7-α6 of SbcD is likely to be a molecular switch and plays an important role in the regulation of substrate binding, catalytic reaction and state transitions. Based on structural and mutational analyses, a novel ssDNA-binding model of SbcD is proposed, providing insight into the catalytic mechanism of DSBs repair by the Mre11 complex.