Bugreev Dmitry V, Mazin Alexander V
Department of Biochemistry, Drexel University College of Medicine, Philadelphia, PA 19102-1192, USA.
Proc Natl Acad Sci U S A. 2004 Jul 6;101(27):9988-93. doi: 10.1073/pnas.0402105101. Epub 2004 Jun 28.
Human Rad51 (hRad51) protein plays a key role in homologous recombination and DNA repair. hRad51 protein forms a helical filament on single-stranded DNA (ssDNA), which performs the basic steps of homologous recombination: a search for homologous double-stranded DNA (dsDNA) and DNA strand exchange. hRad51 protein possesses DNA-dependent ATPase activity; however, the role of this activity has not been understood. Our current results show that Ca(2+) greatly stimulates DNA strand exchange activity of hRad51 protein. We found that Ca(2+) exerts its stimulatory effect by modulating the ATPase activity of hRad51 protein. Our data demonstrate that, in the presence of Mg(2+), the hRad51-ATP-ssDNA filament is quickly converted to an inactive hRad51-ADP-ssDNA form, due to relatively rapid ATP hydrolysis and slow dissociation of ADP. Ca(2+) maintains the active hRad51-ATP-ssDNA filament by reducing the ATP hydrolysis rate. These findings demonstrate a crucial role of the ATPase activity in regulation of DNA strand exchange activity of hRad51 protein. This mechanism of Rad51 protein regulation by modulating its ATPase activity is evolutionarily recent; we found no such mechanism for yeast Rad51 (yRad51) protein.
人类Rad51（hRad51）蛋白在同源重组和DNA修复中起关键作用。hRad51蛋白在单链DNA（ssDNA）上形成螺旋丝，执行同源重组的基本步骤：寻找同源双链DNA（dsDNA）和DNA链交换。hRad51蛋白具有依赖DNA的ATP酶活性；然而，这种活性的作用尚未明确。我们目前的结果表明，Ca(2+) 极大地刺激了hRad51蛋白的DNA链交换活性。我们发现Ca(2+) 通过调节hRad51蛋白的ATP酶活性发挥其刺激作用。我们的数据表明，在Mg(2+) 存在的情况下，由于ATP相对快速水解和ADP缓慢解离，hRad51-ATP-ssDNA丝迅速转变为无活性的hRad51-ADP-ssDNA形式。Ca(2+) 通过降低ATP水解速率维持活性hRad51-ATP-ssDNA丝。这些发现证明了ATP酶活性在调节hRad51蛋白的DNA链交换活性中的关键作用。通过调节其ATP酶活性来调节Rad51蛋白的这种机制是最近才进化出来的；我们没有发现酵母Rad51（yRad51）蛋白有这样的机制。
