Institute of Immunology and Experimental Therapy, Polish Academy of Sciences, Department of Microbiology, Weigla 12, 53-114 Wrocław, Poland.
J Mol Biol. 2011 Apr 29;408(2):238-51. doi: 10.1016/j.jmb.2011.02.045. Epub 2011 Feb 25.
Replication of the bacterial chromosome is initiated by binding the DnaA protein to oriC. Various factors control the ability of DnaA to bind and unwind DNA. Among them, Escherichia coli DiaA and Helicobacter pylori HobA have been characterized recently. They were found to interact with domain I of DnaA and stimulate DnaA binding to oriC. We examined HobA and DiaA functional homology and showed that, despite a high degree of structural similarity, they are not interchangeable because they are unable to interact with heterologous DnaA proteins. We revealed particular structural differences impeding formation of heterologous complexes and, consistently, we restored DiaA-enhanced oriC binding by the hybrid Ec(I)-Hp(II-IV)DnaA protein; i.e. H. pylori DnaA in which domain I was exchanged with that of E. coli. This proved that DiaA and HobA are functional homologs and upon binding to DnaA they exert a similar effect on orisome formation. Interestingly, we showed for the first time that the dynamics of DiaA- and HobA-stimulated orisome assembly are different. HobA enhances and accelerates HpDnaA binding to oriC, whereas DiaA increases but decelerates EcDnaA binding with oriC. We postulate that the different dynamics of orisome formation reflect the distinct strategies adopted by E. coli and H. pylori to regulate the frequency of the replication of their chromosomes. DiaA/HobA homolog have been identified in many proteobacteria and therefore might constitute a common, though species-specific, factor modulating bacterial orisome assembly.
细菌染色体的复制是通过 DnaA 蛋白与 oriC 的结合启动的。各种因素控制着 DnaA 结合和解旋 DNA 的能力。其中，最近已经对大肠杆菌 DiaA 和幽门螺杆菌 HobA 进行了特征描述。发现它们与 DnaA 的结构域 I 相互作用并刺激 DnaA 与 oriC 的结合。我们研究了 HobA 和 DiaA 的功能同源性，并表明尽管它们具有高度的结构相似性，但它们不能互换，因为它们不能与异源 DnaA 蛋白相互作用。我们揭示了特定的结构差异，阻碍了异源复合物的形成，并且一致地，我们通过杂交 Ec（I）-Hp（II-IV）DnaA 蛋白恢复了 DiaA 增强的 oriC 结合；即，幽门螺杆菌 DnaA 中结构域 I 被大肠杆菌的结构域 I 取代。这证明了 DiaA 和 HobA 是功能同源物，并且在与 DnaA 结合时，它们对 ori 体形成产生相似的影响。有趣的是，我们首次表明 DiaA 和 HobA 刺激 ori 体组装的动力学不同。HobA 增强并加速 HpDnaA 与 oriC 的结合，而 DiaA 增加但减慢 EcDnaA 与 oriC 的结合。我们假设 ori 体形成的不同动力学反映了大肠杆菌和幽门螺杆菌采用的不同策略来调节它们染色体复制的频率。DiaA/HobA 同源物已在许多变形菌中被鉴定出来，因此可能构成一种共同的、尽管是物种特异性的、调节细菌 ori 体组装的因素。
