Schneider S, Zhang W, Soultanas P, Paoli M
Centre for Biomolecular Sciences, University of Nottingham, University Park, Nottingham NG7 2RD, UK.
J Mol Biol. 2008 Mar 7;376(5):1237-50. doi: 10.1016/j.jmb.2007.12.045. Epub 2007 Dec 28.
DnaD is a primosomal protein that remodels supercoiled plasmids. It binds to supercoiled forms and converts them to open forms without nicking. During this remodeling process, all the writhe is converted to twist and the plasmids are held around the periphery of large scaffolds made up of DnaD molecules. This DNA-remodeling function is the sum of a scaffold-forming activity on the N-terminal domain and a DNA-dependent oligomerization activity on the C-terminal domain. We have determined the crystal structure of the scaffold-forming N-terminal domain, which reveals a winged-helix architecture, with additional structural elements extending from both N- and C-termini. Four monomers form dimers that join into a tetramer. The N-terminal extension mediates dimerization and tetramerization, with extensive interactions and distinct interfaces. The wings and helices of the winged-helix domains remain exposed on the surface of the tetramer. Structure-guided mutagenesis and atomic force microscopy imaging indicate that these elements, together with the C-terminal extension, are involved in scaffold formation. Based upon our data, we propose a model for the DnaD-mediated scaffold formation.
DnaD是一种引发体蛋白，可重塑超螺旋质粒。它与超螺旋形式结合，将其转化为开放形式而不产生切口。在这个重塑过程中，所有的扭曲都转化为缠绕，质粒围绕由DnaD分子组成的大型支架的周边。这种DNA重塑功能是N端结构域的支架形成活性和C端结构域的DNA依赖性寡聚化活性的总和。我们已经确定了支架形成N端结构域的晶体结构，该结构揭示了一种带翼螺旋结构，N端和C端都有额外的结构元件延伸。四个单体形成二聚体，二聚体再结合成四聚体。N端延伸介导二聚化和四聚化，具有广泛的相互作用和独特的界面。带翼螺旋结构域的翼和螺旋在四聚体表面保持暴露。结构导向诱变和原子力显微镜成像表明，这些元件与C端延伸一起参与支架形成。基于我们的数据，我们提出了一个DnaD介导的支架形成模型。
