A CTP-dependent gating mechanism enables ParB spreading on DNA.
A CTP-dependent gating mechanism enables ParB spreading on DNA.
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作者：
Jalal AS;Tran NT;Stevenson CE;Chimthanawala A;Badrinarayanan A;Lawson DM;Le TB
正确的染色体分离在所有生物体中都是必不可少的。ParA-ParB-parS系统广泛用于细菌染色体分离。先前，我们表明新月柄杆菌ParB需要胞苷三磷酸以逃离成核位点parS并通过滑动到邻近DNA而扩散（Jalal等人，2020年）。在这里，我们提供了这种过渡的结构基础，从成核扩展解决共晶结构的C-末端域截断C。crescentus ParB与parS和CTP类似物。ParB成核是一个开放钳，其中parS在DNA结合结构域（DNA门）处被捕获。在结合CTP时，N末端结构域（NTD）自二聚化以关闭钳的NTD门。DNA门也关闭，从而驱动parS进入DNA门和C端结构域之间的区室。CTP水解和/或水解产物的释放可能与重新打开门以释放DNA和再循环ParB相关。总的来说，我们提出了一个CTP操作的门控机制，调节ParB成核，扩散和回收。
Proper chromosome segregation is essential in all living organisms. The ParA-ParB-parS system is widely employed for chromosome segregation in bacteria. Previously, we showed that Caulobacter crescentus ParB requires cytidine triphosphate to escape the nucleation site parS 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 C. crescentus ParB with parS and with a CTP analog. Nucleating ParB is an open clamp, in which parS 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 parS 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.