Max Planck Research Group Chromosome Organization and Dynamics, Max Planck Institute of Biochemistry, Martinsried, Germany.
Nat Struct Mol Biol. 2013 Mar;20(3):371-9. doi: 10.1038/nsmb.2488. Epub 2013 Jan 27.
Eukaryotic structural maintenance of chromosomes (SMC)-kleisin complexes form large, ring-shaped assemblies that promote accurate chromosome segregation. Their asymmetric structural core comprises SMC heterodimers that associate with both ends of a kleisin subunit. However, prokaryotic condensin Smc-ScpAB is composed of symmetric Smc homodimers associated with the kleisin ScpA in a postulated symmetrical manner. Here, we demonstrate that Smc molecules have two distinct binding sites for ScpA. The N terminus of ScpA binds the Smc coiled coil, whereas the C terminus binds the Smc ATPase domain. We show that in Bacillus subtilis cells, an Smc dimer is bridged by a single ScpAB to generate asymmetric tripartite rings analogous to eukaryotic SMC complexes. We define a molecular mechanism that ensures asymmetric assembly, and we conclude that the basic architecture of SMC-kleisin rings evolved before the emergence of eukaryotes.
真核生物染色体结构维持（SMC）-kleisin 复合物形成大型环状组装体，促进染色体的准确分离。它们的不对称结构核心由 SMC 异二聚体组成，与 kleisin 亚基的两端结合。然而，原核 condensin Smc-ScpAB 由对称的 Smc 同二聚体组成，以假设的对称方式与 kleisin ScpA 结合。在这里，我们证明 Smc 分子有两个用于 ScpA 的不同结合位点。ScpA 的 N 端结合 Smc 卷曲螺旋，而 C 端结合 Smc ATP 酶结构域。我们表明，在枯草芽孢杆菌细胞中，单个 ScpAB 将 Smc 二聚体桥接，形成类似于真核 SMC 复合物的不对称三分体环。我们定义了一个确保不对称组装的分子机制，并得出结论，SMC-kleisin 环的基本结构在真核生物出现之前就已经进化。
