Department of Microbiology and Molecular Genetics, UTHealth Houston McGovern Medical School, Houston, Texas, USA.
mBio. 2024 Aug 14;15(8):e0168724. doi: 10.1128/mbio.01687-24. Epub 2024 Jul 23.
The actin-like FtsA protein is essential for function of the cell division machinery, or divisome, in many bacteria including . Previous studies demonstrated that purified wild-type FtsA assembles into closed mini-rings on lipid membranes, but oligomeric variants of FtsA such as FtsA and FtsA can bypass certain divisome defects and form arc and double-stranded (DS) oligomeric states, respectively, which may reflect conversion of an inactive to an active form of FtsA. However, it remains unproven which oligomeric forms of FtsA are responsible for assembling and activating the divisome. Here, we used an crosslinking assay for FtsA DS filaments to show that they largely depend on proper divisome assembly and are prevalent at later stages of cell division. We also used a previously reported variant that fails to assemble DS filaments, FtsA, to investigate the roles of FtsA oligomeric states in divisome assembly and activation. We show that FtsA cannot form DS filaments , fails to replace native FtsA, and confers a dominant negative phenotype, underscoring the importance of the DS filament stage for FtsA function. Surprisingly, however, activation of the divisome through the * or * superfission alleles suppressed the dominant negative phenotype and rescued the functionality of FtsA. Our results suggest that FtsA DS filaments are needed for divisome activation once it is assembled, but they are not essential for divisome assembly or guiding septum synthesis.IMPORTANCECell division is fundamental for cellular duplication. In simple cells like bacteria, the actin homolog FtsA is essential for cell division and assembles into a variety of protein filaments at the cytoplasmic membrane. These filaments not only help tether polymers of the tubulin-like FtsZ to the membrane at early stages of cell division but also play crucial roles in recruiting other cell division proteins to a complex called the divisome. Once assembled, the divisome subsequently activates synthesis of the division septum that splits the cell in two. One recently discovered oligomeric conformation of FtsA is an antiparallel double-stranded filament. Using a combination of crosslinking and genetics, we provide evidence suggesting that these FtsA double filaments have a crucial role in activating the septum synthesis enzymes.
肌动蛋白样 FtsA 蛋白对于许多细菌（包括 ）的细胞分裂机制或分裂体的功能至关重要。之前的研究表明，纯化的野生型 FtsA 可在脂质膜上组装成封闭的迷你环，但 FtsA 的寡聚变体，如 FtsA 和 FtsA 可以绕过某些分裂体缺陷，分别形成弧形和双链（DS）寡聚态，这可能反映了 FtsA 从无活性形式向活性形式的转变。然而，哪种 FtsA 寡聚形式负责组装和激活分裂体仍未得到证实。在这里，我们使用 FtsA DS 细丝的交联测定法表明，它们在很大程度上取决于正确的分裂体组装，并且在细胞分裂的后期阶段普遍存在。我们还使用了一种以前报道的无法组装 DS 细丝的变体 FtsA 来研究 FtsA 寡聚态在分裂体组装和激活中的作用。我们表明 FtsA 不能形成 DS 细丝，不能替代天然 FtsA，并且赋予显性负表型，突出了 DS 细丝阶段对 FtsA 功能的重要性。然而，令人惊讶的是，通过 或 超分裂等位基因激活分裂体，抑制了显性负表型并挽救了 FtsA 的功能。我们的结果表明，一旦组装完成，FtsA DS 细丝对于分裂体的激活是必需的，但它们对于分裂体的组装或引导隔膜合成不是必需的。重要性细胞分裂是细胞复制的基础。在简单的细胞如 细菌中，肌动蛋白同源物 FtsA 对于细胞分裂是必不可少的，并且在细胞质膜上组装成各种蛋白丝。这些细丝不仅有助于在细胞分裂的早期阶段将微管蛋白样 FtsZ 的聚合物固定在膜上，而且在将其他细胞分裂蛋白募集到称为分裂体的复合物中也起着至关重要的作用。一旦组装完成，分裂体随后激活分隔物的合成，将细胞分成两部分。FtsA 的一种最近发现的寡聚构象是反平行双链丝。我们使用交联和遗传学的组合提供了证据，表明这些 FtsA 双链丝在激活隔膜合成酶方面起着关键作用。
