Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, Delft, the Netherlands.
Cell Biology and Biophysics Unit, Structural and Computational Unit, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany.
Nat Struct Mol Biol. 2020 Dec;27(12):1134-1141. doi: 10.1038/s41594-020-0508-3. Epub 2020 Sep 28.
Structural maintenance of chromosome (SMC) protein complexes are the key organizers of the spatiotemporal structure of chromosomes. The condensin SMC complex has recently been shown to be a molecular motor that extrudes large loops of DNA, but the mechanism of this unique motor remains elusive. Using atomic force microscopy, we show that budding yeast condensin exhibits mainly open 'O' shapes and collapsed 'B' shapes, and it cycles dynamically between these two states over time, with ATP binding inducing the O to B transition. Condensin binds DNA via its globular domain and also via the hinge domain. We observe a single condensin complex at the stem of extruded DNA loops, where the neck size of the DNA loop correlates with the width of the condensin complex. The results are indicative of a type of scrunching model in which condensin extrudes DNA by a cyclic switching of its conformation between O and B shapes.
染色体结构维持（SMC）蛋白复合物是染色体时空结构的关键组织者。最近已经表明，凝聚素 SMC 复合物是一种分子马达，可以挤出 DNA 的大环，但这种独特的马达的机制仍然难以捉摸。使用原子力显微镜，我们表明 budding 酵母凝聚素主要表现为开放的“O”形和塌陷的“B”形，并且随着时间的推移，它在这两种状态之间动态循环，ATP 结合诱导 O 到 B 的转变。凝聚素通过其球状结构域和铰链结构域与 DNA 结合。我们在挤出的 DNA 环的茎部观察到单个凝聚素复合物，其中 DNA 环的颈部尺寸与凝聚素复合物的宽度相关。结果表明，在这种挤压模型中，凝聚素通过其构象在 O 形和 B 形之间的循环切换来挤出 DNA。
