ATP- and GTP-dependent molecular switches are extensively used to control functions of proteins in a wide range of biological processes. However, CTP switches are rarely reported. Here, we report that a nucleoid occlusion protein Noc is a CTPase enzyme whose membrane-binding activity is directly regulated by a CTP switch. In Bacillus subtilis, Noc nucleates on 16 bp NBS sites before associating with neighboring non-specific DNA to form large membrane-associated nucleoprotein complexes to physically occlude assembly of the cell division machinery. By in vitro reconstitution, we show that (1) CTP is required for Noc to form the NBS-dependent nucleoprotein complex, and (2) CTP binding, but not hydrolysis, switches Noc to a membrane-active state. Overall, we suggest that CTP couples membrane-binding activity of Noc to nucleoprotein complex formation to ensure productive recruitment of DNA to the bacterial cell membrane for nucleoid occlusion activity.

ATP 和 GTP 依赖性分子开关广泛用于控制蛋白质在各种生物过程中的功能。然而，CTP 开关很少被报道。在这里，我们报告了类核封闭蛋白 Noc 是一种 CTPase 酶，其膜结合活性由 CTP 开关直接调节。在枯草芽孢杆菌中，Noc 在 16 bp NBS位点上成核，然后与相邻的非特异性 DNA 结合形成大的膜相关核蛋白复合物，从而物理阻断细胞分裂机制的组装。通过体外重组，我们表明 (1) Noc 需要 CTP 才能形成NBS依赖的核蛋白复合物和 (2) CTP 结合，但不是水解，将 Noc 切换到膜活性状态。总体而言，我们建议 CTP 将 Noc 的膜结合活性与核蛋白复合物的形成结合起来，以确保将 DNA 有效地募集到细菌细胞膜以实现类核闭塞活性。