Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, Delft, Netherlands.
Max Planck Institute of Biophysics, Frankfurt am Main, Germany.
Nat Struct Mol Biol. 2022 Jul;29(7):719-727. doi: 10.1038/s41594-022-00802-x. Epub 2022 Jul 14.
Condensin, a structural maintenance of chromosomes (SMC) complex, has been shown to be a molecular motor protein that organizes chromosomes by extruding loops of DNA. In cells, such loop extrusion is challenged by many potential conflicts, for example, the torsional stresses that are generated by other DNA-processing enzymes. It has so far remained unclear how DNA supercoiling affects loop extrusion. Here, we use time-lapse single-molecule imaging to study condensin-driven DNA loop extrusion on supercoiled DNA. We find that condensin binding and DNA looping are stimulated by positively supercoiled DNA, and condensin preferentially binds near the tips of supercoiled plectonemes. Upon loop extrusion, condensin collects nearby plectonemes into a single supercoiled loop that is highly stable. Atomic force microscopy imaging shows that condensin generates supercoils in the presence of ATP. Our findings provide insight into the topology-regulated loading and formation of supercoiled loops by SMC complexes and clarify the interplay of loop extrusion and supercoiling.
凝聚素（Condensin）是一种结构维持染色体（SMC）复合物，已被证明是一种分子马达蛋白，通过挤出 DNA 环来组织染色体。在细胞中，这种环挤出受到许多潜在冲突的挑战，例如，由其他 DNA 处理酶产生的扭曲力。到目前为止，人们还不清楚 DNA 超螺旋如何影响环挤出。在这里，我们使用延时单分子成像来研究凝聚素驱动的超螺旋 DNA 上的 DNA 环挤出。我们发现，凝聚素结合和 DNA 环化受到正超螺旋 DNA 的刺激，并且凝聚素优先结合在超螺旋扭结的尖端附近。在环挤出过程中，凝聚素将附近的扭结收集到一个高度稳定的单个超螺旋环中。原子力显微镜成像显示，在 ATP 存在的情况下，凝聚素会产生超螺旋。我们的发现为 SMC 复合物通过拓扑调节加载和形成超螺旋环提供了深入的了解，并阐明了环挤出和超螺旋之间的相互作用。
