Ragone Stefania, Maman Joseph D, Furnham Nicholas, Pellegrini Luca
Department of Biochemistry, University of Cambridge, Cambridge, UK.
EMBO J. 2008 Aug 20;27(16):2259-69. doi: 10.1038/emboj.2008.145. Epub 2008 Jul 24.
The RecA/RAD51 nucleoprotein filament is central to the reaction of homologous recombination (HR). Filament activity must be tightly regulated in vivo as unrestrained HR can cause genomic instability. Our mechanistic understanding of HR is restricted by lack of structural information about the regulatory proteins that control filament activity. Here, we describe a structural and functional analysis of the HR inhibitor protein RecX and its mode of interaction with the RecA filament. RecX is a modular protein assembled of repeated three-helix motifs. The relative arrangement of the repeats generates an elongated and curved shape that is well suited for binding within the helical groove of the RecA filament. Structure-based mutagenesis confirms that conserved basic residues on the concave side of RecX are important for repression of RecA activity. Analysis of RecA filament dynamics in the presence of RecX shows that RecX actively promotes filament disassembly. Collectively, our data support a model in which RecX binding to the helical groove of the filament causes local dissociation of RecA protomers, leading to filament destabilisation and HR inhibition.
RecA/RAD51核蛋白丝对于同源重组（HR）反应至关重要。由于不受控制的HR会导致基因组不稳定，因此在体内必须严格调节丝活性。我们对HR的机制理解受到缺乏控制丝活性的调节蛋白结构信息的限制。在这里，我们描述了HR抑制剂蛋白RecX的结构和功能分析及其与RecA丝的相互作用模式。RecX是一种由重复的三螺旋基序组装而成的模块化蛋白。重复序列的相对排列产生了细长且弯曲的形状，非常适合结合在RecA丝的螺旋凹槽内。基于结构的诱变证实，RecX凹面侧的保守碱性残基对于抑制RecA活性很重要。在RecX存在下对RecA丝动力学的分析表明，RecX积极促进丝的解聚。总体而言，我们的数据支持一个模型，即RecX与丝的螺旋凹槽结合会导致RecA原聚体的局部解离，从而导致丝不稳定和HR抑制。
