Ca2+ improves organization of single-stranded DNA bases in human Rad51 filament, explaining stimulatory effect on gene recombination
Ca2+ improves organization of single-stranded DNA bases in human Rad51 filament, explaining stimulatory effect on gene recombination
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DOI：
10.1093/nar/gks140
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发表时间：
2012-06-01
影响因子：
14.9
通讯作者：
Norden, Bengt
中科院分区：
文献类型：
--
作者：
Fornander, Louise H.;Frykholm, Karolin;Norden, Bengt
人RAD 51蛋白（HsRad 51）催化用于同源重组的DNA链交换反应。为了澄清的分子机制的反应在体外更有效的存在下的Ca 2+比Mg 2+，我们已经研究了这些离子的影响HsRad 51细丝复合物的结构与单链和双链DNA，反应中间体。流动线性二色性光谱表明，这两种离子条件诱导显着不同的结构中的HsRad 51/单链DNA复合物，而HsRad 51/双链DNA复合物不表现出这种离子依赖性。在HsRad 51/单链DNA丝中，链交换反应的主要中间体，ATP/Ca 2+诱导DNA的有序构象，优先与相对于丝轴的核碱基垂直取向，而ATP/Mg 2+，ADP/Mg 2+或ADP/Ca 2+的存在下不。ATP/Ca ~（2+）形成的丝具有较高的链交换活性，而其它丝则表现出较低的活性。分子模拟表明，结构变异是由二价阳离子干扰L2环接近DNA结合位点引起的。有人提出，较大的Ca 2+可以稳定环的构象，从而稳定蛋白质与DNA的相互作用。DNA的紧密结合，碱基垂直取向，可以促进链交换。
Human RAD51 protein (HsRad51) catalyses the DNA strand exchange reaction for homologous recombination. To clarify the molecular mechanism of the reaction in vitro being more effective in the presence of Ca2+ than of Mg2+, we have investigated the effect of these ions on the structure of HsRad51 filament complexes with single- and double-stranded DNA, the reaction intermediates. Flow linear dichroism spectroscopy shows that the two ionic conditions induce significantly different structures in the HsRad51/single-stranded DNA complex, while the HsRad51/double-stranded DNA complex does not demonstrate this ionic dependence. In the HsRad51/single-stranded DNA filament, the primary intermediate of the strand exchange reaction, ATP/Ca2+ induces an ordered conformation of DNA, with preferentially perpendicular orientation of nucleobases relative to the filament axis, while the presence of ATP/Mg2+, ADP/Mg2+ or ADP/Ca2+ does not. A high strand exchange activity is observed for the filament formed with ATP/Ca2+, whereas the other filaments exhibit lower activity. Molecular modelling suggests that the structural variation is caused by the divalent cation interfering with the L2 loop close to the DNA-binding site. It is proposed that the larger Ca2+ stabilizes the loop conformation and thereby the protein-DNA interaction. A tight binding of DNA, with bases perpendicularly oriented, could facilitate strand exchange.