Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts, USA.
PLoS Genet. 2013;9(2):e1003304. doi: 10.1371/journal.pgen.1003304. Epub 2013 Feb 14.
Bacterial cells use chromosome-associated division inhibitors to help coordinate the processes of DNA replication and segregation with cytokinesis. SlmA from Escherichia coli, a member of the tetracycline repressor (TetR)-like protein family, is one example of this class of regulator. It blocks the assembly of the bacterial cytokinetic ring by interfering with the polymerization of the tubulin-like FtsZ protein in a manner that is dramatically stimulated upon specific DNA binding. Here we used a combination of molecular genetics and biochemistry to identify the active site of SlmA responsible for disrupting FtsZ polymerization. Interestingly, this site maps to a region of SlmA that in the published DNA-free structure is partially occluded by the DNA-binding domains. In this conformation, the SlmA structure resembles the drug/inducer-bound conformers of other TetR-like proteins, which in the absence of inducer require an inward rotation of their DNA-binding domains to bind successive major grooves on operator DNA. Our results are therefore consistent with a model in which DNA-binding activates SlmA by promoting a rotational movement of the DNA-binding domains that fully exposes the FtsZ-binding sites. SlmA may thus represent a special subclass of TetR-like proteins that have adapted conformational changes normally associated with inducer sensing in order to modulate an interaction with a partner protein. In this case, the adaptation ensures that SlmA only blocks cytokinesis in regions of the cell occupied by the origin-proximal portion of the chromosome where SlmA-binding sites are enriched.
细菌细胞利用染色体相关的分裂抑制剂来帮助协调 DNA 复制和分离与胞质分裂的过程。大肠杆菌中的 SlmA 是四环类抗生物质阻抑蛋白（TetR-like protein）家族的成员之一，就是这类调控因子的一个例子。它通过干扰类似微管蛋白的 FtsZ 蛋白的聚合来阻止细菌胞质分裂环的组装，这种方式在特定的 DNA 结合时会被显著地刺激。在这里，我们使用了分子遗传学和生物化学的组合方法来鉴定负责破坏 FtsZ 聚合的 SlmA 的活性位点。有趣的是，这个位点映射到 SlmA 的一个区域，在已发表的无 DNA 结构中，该区域部分被 DNA 结合结构域所掩盖。在这种构象中，SlmA 结构类似于其他 TetR-like 蛋白的药物/诱导剂结合构象，在没有诱导剂的情况下，它们需要 DNA 结合结构域向内旋转才能结合操纵子 DNA 上的连续主要凹槽。因此，我们的结果与一个模型一致，即 DNA 结合通过促进 DNA 结合结构域的旋转运动来激活 SlmA，从而完全暴露 FtsZ 结合位点。SlmA 可能因此代表了一类特殊的 TetR-like 蛋白，它们已经适应了通常与诱导剂感应相关的构象变化，以调节与伴侣蛋白的相互作用。在这种情况下，这种适应性确保 SlmA 仅在细胞中被染色体起始近端部分占据的区域阻止胞质分裂，在这些区域中 SlmA 结合位点丰富。
