Chromosome Dynamics Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Department of Life Science, College of Science, Rikkyo University, 3-34-1 Nishi-Ikebukuro, Toshima-ku, Tokyo, 171-8501, Japan.
Structure. 2017 Apr 4;25(4):603-616.e4. doi: 10.1016/j.str.2017.02.008. Epub 2017 Mar 9.
The SMC-ScpAB complex plays a crucial role in chromosome organization and segregation in many bacteria. It is composed of a V-shaped SMC dimer and an ScpAB subcomplex that bridges the two Structural Maintenance of Chromosomes (SMC) head domains. Despite its functional significance, the mechanistic details of SMC-ScpAB remain obscure. Here we provide evidence that ATP-dependent head-head engagement induces a lever movement of the SMC neck region, which might help to separate juxtaposed coiled-coil arms. Binding of the ScpA N-terminal domain (NTD) to the SMC neck region is negatively regulated by the ScpB C-terminal domain. Mutations in the ScpA NTD compromise this regulation and profoundly affect the overall shape of the complex. The SMC hinge domain is structurally relaxed when free from coiled-coil juxtaposition. Taken together, we propose that the structural parts of SMC-ScpAB are subjected to the balance between constraint and relaxation, cooperating to modulate dynamic conformational changes of the whole complex.
SMC-ScpAB 复合物在许多细菌的染色体组织和分离中起着至关重要的作用。它由一个 V 形的 SMC 二聚体和一个 ScpAB 亚基组成，该亚基连接两个结构维护染色体（SMC）头部结构域。尽管其功能意义重大，但 SMC-ScpAB 的机械细节仍然不清楚。在这里，我们提供的证据表明，ATP 依赖性的头对头结合诱导 SMC 颈部区域的杠杆运动，这可能有助于分离相邻的螺旋卷曲臂。ScpA N 端结构域（NTD）与 SMC 颈部区域的结合受到 ScpB C 端结构域的负调控。ScpA NTD 中的突变破坏了这种调控，并严重影响了复合物的整体形状。当 SMC 没有与螺旋卷曲臂并列时，其铰链结构域在结构上是放松的。总的来说，我们提出 SMC-ScpAB 的结构部分受到约束和放松之间的平衡的影响，共同调节整个复合物的动态构象变化。
