School of Environmental and Life Sciences, University of Newcastle, University Drive, Callaghan NSW 2308, Australia.
Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, United Kingdom.
Sci Rep. 2016 Oct 6;6:33357. doi: 10.1038/srep33357.
Bacterial chromosomes are most often circular DNA molecules. This can produce a topological problem; a genetic crossover from homologous recombination results in dimerization of the chromosome. A chromosome dimer is lethal unless resolved. A site-specific recombination system catalyses this dimer-resolution reaction at the chromosomal site dif. In Escherichia coli, two tyrosine-family recombinases, XerC and XerD, bind to dif and carry out two pairs of sequential strand exchange reactions. However, what makes the reaction unique among site-specific recombination reactions is that the first step, XerD-mediated strand exchange, relies on interaction with the very C-terminus of the FtsK DNA translocase. FtsK is a powerful molecular motor that functions in cell division, co-ordinating division with clearing chromosomal DNA from the site of septation and also acts to position the dif sites for recombination. This is a model system for unlinking, separating and segregating large DNA molecules. Here we describe the molecular detail of the interaction between XerD and FtsK that leads to activation of recombination as deduced from a co-crystal structure, biochemical and in vivo experiments. FtsKγ interacts with the C-terminal domain of XerD, above a cleft where XerC is thought to bind. We present a model for activation of recombination based on structural data.
细菌染色体通常是圆形的 DNA 分子。这会产生一个拓扑学问题；同源重组导致的基因交叉会导致染色体二聚化。染色体二聚体是致命的，除非得到解决。一种特定于位点的重组系统在染色体位点 dif 处催化这个二聚体的解决反应。在大肠杆菌中，两种酪氨酸家族重组酶 XerC 和 XerD 结合到 dif 上，并进行两对连续的链交换反应。然而，使这个反应在特定于位点的重组反应中独一无二的是，第一步 XerD 介导的链交换依赖于与 FtsK DNA 转位酶的非常 C 末端的相互作用。FtsK 是一种强大的分子马达，在细胞分裂中起作用，协调分裂与从分隔部位清除染色体 DNA，并作用于定位 dif 位点以进行重组。这是一个用于分离、分离和分配大 DNA 分子的模型系统。在这里，我们描述了 XerD 和 FtsK 之间的相互作用的分子细节，该相互作用来自于共结晶结构、生化和体内实验，导致了重组的激活。FtsKγ 与 XerD 的 C 末端结构域相互作用，该结构域位于认为 XerC 结合的裂隙上方。我们根据结构数据提出了一个重组激活的模型。
