Structural Biology Group, European Synchrotron Radiation Facility, BP 220 38043 Grenoble Cedex 9, France.
Structure. 2012 Mar 7;20(3):554-64. doi: 10.1016/j.str.2012.01.020.
Hexameric DnaB helicases are often loaded at DNA replication forks by interacting with the initiator protein DnaA and/or a helicase loader (DnaC in Escherichia coli). These loaders are not universally required, and DnaB from Helicobacter pylori was found to bypass DnaC when expressed in E. coli cells. The crystal structure of Helicobacter pylori DnaB C-terminal domain (HpDnaB-CTD) reveals a large two-helix insertion (named HPI) in the ATPase domain that protrudes away from the RecA fold. Biophysical characterization and electron microscopy (EM) analysis of the full-length protein show that HpDnaB forms head-to-head double hexamers remarkably similar to helicases found in some eukaryotes, archaea, and viruses. The docking of the HpDnaB-CTD structure into EM reconstruction of HpDnaB provides a model that shows how hexamerization of the CTD is facilitated by HPI-HPI interactions. The HpDnaB double-hexamer architecture supports an alternative strategy to load bacterial helicases onto forks in the absence of helicase loaders.
六聚体 DNA 解旋酶通常通过与起始蛋白 DnaA 和/或解旋酶加载器（大肠杆菌中的 DnaC）相互作用而在 DNA 复制叉处加载。这些加载器并非普遍需要，并且在大肠杆菌细胞中表达时，发现幽门螺杆菌的 DnaB 可以绕过 DnaC。幽门螺杆菌 DnaB C 端结构域（HpDnaB-CTD）的晶体结构揭示了 ATP 酶结构域中的一个大双螺旋插入物（命名为 HPI），该插入物从 RecA 折叠处突出。全长蛋白的生物物理特性和电子显微镜（EM）分析表明，HpDnaB 形成了头对头的双六聚体，与一些真核生物、古菌和病毒中的解旋酶非常相似。将 HpDnaB-CTD 结构对接至 HpDnaB 的 EM 重建中，提供了一个模型，该模型显示了 HPI-HPI 相互作用如何促进 CTD 的六聚体化。HpDnaB 双六聚体结构支持在没有解旋酶加载器的情况下将细菌解旋酶加载到叉上的替代策略。
