MRC Laboratory of Molecular Biology, Structural Studies Division, Cambridge Biomedical Campus, Cambridge, UK.
MRC Laboratory of Molecular Biology, Protein and Nucleic Acid Chemistry Division, Cambridge Biomedical Campus, Cambridge, UK.
Mol Cell. 2021 Dec 2;81(23):4891-4906.e8. doi: 10.1016/j.molcel.2021.10.011. Epub 2021 Nov 4.
The ring-like structural maintenance of chromosomes (SMC) complex MukBEF folds the genome of Escherichia coli and related bacteria into large loops, presumably by active DNA loop extrusion. MukBEF activity within the replication terminus macrodomain is suppressed by the sequence-specific unloader MatP. Here, we present the complete atomic structure of MukBEF in complex with MatP and DNA as determined by electron cryomicroscopy (cryo-EM). The complex binds two distinct DNA double helices corresponding to the arms of a plectonemic loop. MatP-bound DNA threads through the MukBEF ring, while the second DNA is clamped by the kleisin MukF, MukE, and the MukB ATPase heads. Combinatorial cysteine cross-linking confirms this topology of DNA loop entrapment in vivo. Our findings illuminate how a class of near-ubiquitous DNA organizers with important roles in genome maintenance interacts with the bacterial chromosome.
环状结构维持染色体（SMC）复合物 MukBEF 将大肠杆菌和相关细菌的基因组折叠成大环，推测是通过活性 DNA 环挤出。MukBEF 在复制末端宏域内的活性受序列特异性卸载器 MatP 抑制。在这里，我们通过电子 cryo 显微镜（cryo-EM）确定了与 MatP 和 DNA 复合物的 MukBEF 完整原子结构。该复合物结合了两条不同的 DNA 双螺旋，对应于扭结环的臂。MatP 结合的 DNA 通过 MukBEF 环，而第二个 DNA 被 kleisin MukF、MukE 和 MukB ATP 酶头夹住。组合半胱氨酸交联证实了这种体内 DNA 环捕获的拓扑结构。我们的发现阐明了一类在基因组维持中具有重要作用的普遍存在的 DNA 组织者如何与细菌染色体相互作用。
