Department of Biology, Washington University, Saint Louis, Missouri 63130, USA.
J Biol Chem. 2012 Mar 30;287(14):10945-57. doi: 10.1074/jbc.M111.330324. Epub 2012 Feb 1.
Bacterial cell division typically requires assembly of the cytoskeletal protein FtsZ into a ring (Z-ring) at the nascent division site that serves as a foundation for assembly of the division apparatus. High resolution imaging suggests that the Z-ring consists of short, single-stranded polymers held together by lateral interactions. Several proteins implicated in stabilizing the Z-ring enhance lateral interactions between FtsZ polymers in vitro. Here we report that residues at the C terminus of Bacillus subtilis FtsZ (C-terminal variable region (CTV)) are both necessary and sufficient for stimulating lateral interactions in vitro in the absence of modulatory proteins. Swapping the 6-residue CTV from B. subtilis FtsZ with the 4-residue CTV from Escherichia coli FtsZ completely abolished lateral interactions between chimeric B. subtilis FtsZ polymers. The E. coli FtsZ chimera readily formed higher order structures normally seen only in the presence of molecular crowding agents. CTV-mediated lateral interactions are important for the integrity of the Z-ring because B. subtilis cells expressing the B. subtilis FtsZ chimera had a low frequency of FtsZ ring formation and a high degree of filamentation relative to wild-type cells. Site-directed mutagenesis of the B. subtilis CTV suggests that electrostatic forces are an important determinant of lateral interaction potential.
细菌细胞分裂通常需要将细胞骨架蛋白 FtsZ 组装成位于新生分裂部位的环（Z 环），作为分裂装置组装的基础。高分辨率成像表明，Z 环由短的单链聚合物组成，通过侧向相互作用保持在一起。几种被认为能稳定 Z 环的蛋白质在体外增强 FtsZ 聚合物之间的侧向相互作用。在这里，我们报告说枯草芽孢杆菌 FtsZ 的 C 末端（C 末端可变区（CTV））残基对于在没有调节蛋白的情况下体外刺激侧向相互作用是必需和充分的。将枯草芽孢杆菌 FtsZ 的 6 个残基 CTV 与大肠杆菌 FtsZ 的 4 个残基 CTV 交换，完全消除了嵌合枯草芽孢杆菌 FtsZ 聚合物之间的侧向相互作用。大肠杆菌 FtsZ 嵌合体很容易形成通常只有在分子拥挤剂存在下才能看到的更高阶结构。CTV 介导的侧向相互作用对于 Z 环的完整性很重要，因为表达枯草芽孢杆菌 FtsZ 嵌合体的枯草芽孢杆菌细胞的 FtsZ 环形成频率较低，与野生型细胞相比，丝状化程度较高。枯草芽孢杆菌 CTV 的定点突变表明，静电相互作用是侧向相互作用潜力的一个重要决定因素。
