Sukhoverkov Kirill V, Balaguer-Perez Francisco, Aicart-Ramos Clara, Tran Ngat T, Maqbool Abbas, Rejzek Martin, Chandra Govind, Moreno-Herrero Fernando, Le Tung B K
Department of Molecular Microbiology, John Innes Centre, Norwich NR4 7UH, United Kingdom.
Department of Macromolecular Structures, Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Científicas, Madrid 28049, Spain.
Proc Natl Acad Sci U S A. 2025 Jul 8;122(27):e2406398122. doi: 10.1073/pnas.2406398122. Epub 2025 Jul 2.
The ATP- and CTP-dependent ParA-ParB- segrosome is a macromolecular complex that segregates chromosomes/plasmids in most bacterial species. CTP binding and hydrolysis enable ParB to slide along DNA and to bridge and condense DNA, thereby dictating the size and dynamics of the tripartite ParAB complex. Several other evolutionarily distinct systems can also segregate DNA, although the full diversity of bacterial DNA partition systems remains unknown. Here, we identify a CTP-independent ParAB system that maintains the conjugative plasmid SCP2 in the filamentous bacterium . We demonstrate that an SCP2 ParB-like protein, ParT, loads onto DNA at an 18-bp site and diffuses away to the adjacent DNA despite lacking an apparent CTPase domain and detectable NTPase activity. We further show that DNA facilitates ParT transition from loading to a diffusing state, allowing ParT to accumulate on DNA, and that ParT activates the ATPase activity of its cognate partner protein, ParA. Additionally, we identify numerous structural homologs of ParT, suggesting that CTP-independent diffusion on DNA might be more common than previously recognized. Overall, our findings reveal a CTP-independent DNA translocation as an alternative and unexpected mechanism for assembling a bacterial DNA segregation complex and suggest that CTP binding and hydrolysis are not universal features of ParAB-like systems.
依赖ATP和CTP的ParA-ParB- 分染色体体是一种大分子复合物，可在大多数细菌物种中分离染色体/质粒。CTP结合和水解使ParB能够沿DNA滑动、桥接并凝聚DNA，从而决定三方ParAB复合物的大小和动态变化。其他几种在进化上不同的系统也能分离DNA，尽管细菌DNA分配系统的全部多样性仍不清楚。在这里，我们鉴定出一种不依赖CTP的ParAB系统，该系统可在丝状细菌中维持接合性质粒SCP2。我们证明，一种SCP2 ParB样蛋白ParT在一个18bp的位点加载到DNA上，并扩散到相邻的DNA上，尽管它缺乏明显的CTP酶结构域和可检测到的NTP酶活性。我们进一步表明，DNA促进ParT从加载状态转变为扩散状态，使ParT在DNA上积累，并且ParT激活其同源伴侣蛋白ParA的ATP酶活性。此外，我们鉴定出了许多ParT的结构同源物，这表明在DNA上不依赖CTP的扩散可能比以前认为的更为普遍。总体而言，我们的研究结果揭示了一种不依赖CTP的DNA易位，这是组装细菌DNA分离复合物的一种替代且意想不到的机制，并表明CTP结合和水解并非ParAB样系统的普遍特征。
