Chao William C H, Murayama Yasuto, Muñoz Sofía, Costa Alessandro, Uhlmann Frank, Singleton Martin R
Lincoln's Inn Fields Laboratory, The Francis Crick Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
Clare Hall Laboratory, The Francis Crick Institute, Blanche Lane, South Mimms, Hertfordshire EN6 3LD, UK.
Cell Rep. 2015 Aug 4;12(5):719-25. doi: 10.1016/j.celrep.2015.06.071. Epub 2015 Jul 23.
The remarkable accuracy of eukaryotic cell division is partly maintained by the cohesin complex acting as a molecular glue to prevent premature sister chromatid separation. The loading of cohesin onto chromosomes is catalyzed by the Scc2-Scc4 loader complex. Here, we report the crystal structure of Scc4 bound to the N terminus of Scc2 and show that Scc4 is a tetratricopeptide repeat (TPR) superhelix. The Scc2 N terminus adopts an extended conformation and is entrapped by the core of the Scc4 superhelix. Electron microscopy (EM) analysis reveals that the Scc2-Scc4 loader complex comprises three domains: a head, body, and hook. Deletion studies unambiguously assign the Scc2N-Scc4 as the globular head domain, whereas in vitro cohesin loading assays show that the central body and the hook domains are sufficient to catalyze cohesin loading onto circular DNA, but not chromatinized DNA in vivo, suggesting a possible role for Scc4 as a chromatin adaptor.
真核细胞分裂的高度准确性部分是由黏连蛋白复合体作为分子胶水来维持的，以防止姐妹染色单体过早分离。黏连蛋白加载到染色体上是由Scc2-Scc4加载复合体催化的。在此，我们报道了与Scc2 N端结合的Scc4的晶体结构，并表明Scc4是一个四肽重复（TPR）超螺旋。Scc2 N端呈伸展构象，并被Scc4超螺旋的核心所包裹。电子显微镜（EM）分析表明，Scc2-Scc4加载复合体由三个结构域组成：头部、主体和钩部。缺失研究明确将Scc2N-Scc4确定为球状头部结构域，而体外黏连蛋白加载试验表明，中央主体和钩部结构域足以催化黏连蛋白加载到环状DNA上，但在体内不能催化其加载到染色质化DNA上，这表明Scc4可能作为一种染色质衔接子发挥作用。
