Schumacher Maria A, Glover Tiffany C, Brzoska Anthony J, Jensen Slade O, Dunham Thomas D, Skurray Ronald A, Firth Neville
Department of Biochemistry and Molecular Biology, University of Texas, M.D. Anderson Cancer Center, Unit 1000, Houston, TX 77030, USA.
Nature. 2007 Dec 20;450(7173):1268-71. doi: 10.1038/nature06392.
The stable inheritance of genetic material depends on accurate DNA partition. Plasmids serve as tractable model systems to study DNA segregation because they require only a DNA centromere, a centromere-binding protein and a force-generating ATPase. The centromeres of partition (par) systems typically consist of a tandem arrangement of direct repeats. The best-characterized par system contains a centromere-binding protein called ParR and an ATPase called ParM. In the first step of segregation, multiple ParR proteins interact with the centromere repeats to form a large nucleoprotein complex of unknown structure called the segrosome, which binds ParM filaments. pSK41 ParR binds a centromere consisting of multiple 20-base-pair (bp) tandem repeats to mediate both transcription autoregulation and segregation. Here we report the structure of the pSK41 segrosome revealed in the crystal structure of a ParR-DNA complex. In the crystals, the 20-mer tandem repeats stack pseudo-continuously to generate the full-length centromere with the ribbon-helix-helix (RHH) fold of ParR binding successive DNA repeats as dimer-of-dimers. Remarkably, the dimer-of-dimers assemble in a continuous protein super-helical array, wrapping the DNA about its positive convex surface to form a large segrosome with an open, solenoid-shaped structure, suggesting a mechanism for ParM capture and subsequent plasmid segregation.
遗传物质的稳定遗传依赖于精确的DNA分配。质粒作为易于处理的模型系统用于研究DNA分离，因为它们仅需要一个DNA着丝粒、一个着丝粒结合蛋白和一个产生力的ATP酶。分配（par）系统的着丝粒通常由直接重复序列的串联排列组成。特征最明确的par系统包含一种名为ParR的着丝粒结合蛋白和一种名为ParM的ATP酶。在分离的第一步，多个ParR蛋白与着丝粒重复序列相互作用，形成一个结构未知的大型核蛋白复合体，称为分离体，它结合ParM细丝。pSK41 ParR结合由多个20碱基对（bp）串联重复序列组成的着丝粒，以介导转录自调控和分离。在这里，我们报告了在ParR-DNA复合体的晶体结构中揭示的pSK41分离体的结构。在晶体中，20聚体串联重复序列伪连续堆叠，生成全长着丝粒，ParR的带状-螺旋-螺旋（RHH）折叠以二聚体的二聚体形式结合连续的DNA重复序列。值得注意的是，二聚体的二聚体以连续的蛋白质超螺旋阵列组装，将DNA包裹在其正凸表面周围，形成一个具有开放的、螺线管状结构的大型分离体，这提示了ParM捕获及随后质粒分离的机制。
