MRC Laboratory of Molecular Biology, Cambridge, UK.
Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, UK.
Nat Struct Mol Biol. 2019 Mar;26(3):227-236. doi: 10.1038/s41594-019-0196-z. Epub 2019 Mar 4.
Structural maintenance of chromosomes (SMC)-kleisin complexes organize chromosomal DNAs in all domains of life, with key roles in chromosome segregation, DNA repair and regulation of gene expression. They function through the entrapment and active translocation of DNA, but the underlying conformational changes are largely unclear. Using structural biology, mass spectrometry and cross-linking, we investigated the architecture of two evolutionarily distant SMC-kleisin complexes: MukBEF from Escherichia coli, and cohesin from Saccharomyces cerevisiae. We show that both contain a dynamic coiled-coil discontinuity, the elbow, near the middle of their arms that permits a folded conformation. Bending at the elbow brings into proximity the hinge dimerization domain and the head-kleisin module, situated at opposite ends of the arms. Our findings favour SMC activity models that include a large conformational change in the arms, such as a relative movement between DNA contact sites during DNA loading and translocation.
结构维持染色体 (SMC)-连接酶复合物在所有生命领域组织染色体 DNA，在染色体分离、DNA 修复和基因表达调控中发挥关键作用。它们通过捕获和主动转运 DNA 发挥作用，但基本的构象变化在很大程度上尚不清楚。我们使用结构生物学、质谱和交联技术研究了两种进化上相距甚远的 SMC-连接酶复合物：来自大肠杆菌的 MukBEF 和来自酿酒酵母的 cohesin。我们表明，这两种复合物都含有一个动态的螺旋-卷曲不连续性，即臂中部的肘，这允许其折叠构象。在肘处弯曲使铰链二聚化结构域和头部-连接酶模块靠近，这两个结构域位于臂的两端。我们的发现支持 SMC 活性模型，其中包括臂的大构象变化，例如在 DNA 加载和转运过程中 DNA 结合位点之间的相对运动。
