Department of Molecular Microbiology, John Innes Centre, Norwich, United Kingdom.
Department of Biochemistry and Metabolism, John Innes Centre, Norwich, United Kingdom.
Elife. 2021 Aug 16;10:e69676. doi: 10.7554/eLife.69676.
Proper chromosome segregation is essential in all living organisms. The ParA-ParB- system is widely employed for chromosome segregation in bacteria. Previously, we showed that ParB requires cytidine triphosphate to escape the nucleation site and spread by sliding to the neighboring DNA (Jalal et al., 2020). Here, we provide the structural basis for this transition from nucleation to spreading by solving co-crystal structures of a C-terminal domain truncated ParB with and with a CTP analog. Nucleating ParB is an open clamp, in which is captured at the DNA-binding domain (the DNA-gate). Upon binding CTP, the N-terminal domain (NTD) self-dimerizes to close the NTD-gate of the clamp. The DNA-gate also closes, thus driving into a compartment between the DNA-gate and the C-terminal domain. CTP hydrolysis and/or the release of hydrolytic products are likely associated with reopening of the gates to release DNA and recycle ParB. Overall, we suggest a CTP-operated gating mechanism that regulates ParB nucleation, spreading, and recycling.
正确的染色体分离对于所有生物都是至关重要的。ParA-ParB 系统被广泛用于细菌的染色体分离。以前，我们表明 ParB 需要三磷酸胞苷才能逃离成核位点，并通过滑动到相邻的 DNA 上进行传播 (Jalal 等人，2020)。在这里，我们通过解决带有 和 CTP 类似物的 C 端结构域截断 ParB 的共结晶结构，为从成核到传播的这种转变提供了结构基础。成核 ParB 是一种开放的夹钳，其中 被捕获在 DNA 结合域（DNA 门）中。结合 CTP 后，N 端结构域 (NTD) 自身二聚化以关闭夹钳的 NTD 门。DNA 门也关闭，从而将 驱动到 DNA 门和 C 端结构域之间的隔室中。CTP 水解和/或水解产物的释放可能与门的重新打开有关，以释放 DNA 并回收 ParB。总的来说，我们提出了一个 CTP 操作的门控机制，该机制调节 ParB 的成核、传播和回收。
