MICALIS, INRA, AgroParisTech, Université Paris-Saclay, Jouy-en-Josas, France.
Inovarion, Paris, France.
mBio. 2019 Jan 29;10(1):e01879-18. doi: 10.1128/mBio.01879-18.
The actin-like MreB protein is a key player of the machinery controlling the elongation and maintenance of the cell shape of most rod-shaped bacteria. This protein is known to be highly dynamic, moving along the short axis of cells, presumably reflecting the movement of cell wall synthetic machineries during the enzymatic assembly of the peptidoglycan mesh. The ability of MreB proteins to form polymers is not debated, but their structure, length, and conditions of establishment have remained unclear and the subject of conflicting reports. Here we analyze various strains of , the model for Gram-positive bacteria, and we show that MreB forms subdiffraction-limited, less than 200 nm-long nanofilaments on average during active growth, while micron-long filaments are a consequence of artificial overaccumulation of the protein. Our results also show the absence of impact of the size of the filaments on their speed, orientation, and other dynamic properties conferring a large tolerance to toward the levels and consequently the lengths of MreB polymers. Our data indicate that the density of mobile filaments remains constant in various strains regardless of their MreB levels, suggesting that another factor determines this constant. The construction of the bacterial cell envelope is a fundamental topic, as it confers its integrity to bacteria and is consequently the target of numerous antibiotics. MreB is an essential protein suspected to regulate the cell wall synthetic machineries. Despite two decades of study, its localization remains the subject of controversies, its description ranging from helical filaments spanning the entire cell to small discrete entities. The true structure of these filaments is important because it impacts the model describing how the machineries building the cell wall are associated, how they are coordinated at the scale of the entire cell, and how MreB mediates this regulation. Our results shed light on this debate, revealing the size of native filaments in during growth. They argue against models where MreB filament size directly affects the speed of synthesis of the cell wall and where MreB would coordinate distant machineries along the side wall.
肌动蛋白样 MreB 蛋白是控制大多数杆状细菌细胞伸长和维持形状的机械的关键参与者。已知该蛋白高度动态，沿细胞的短轴移动，推测反映了细胞壁合成机械在肽聚糖网格的酶组装过程中移动。MreB 蛋白形成聚合物的能力没有争议，但它们的结构、长度和建立条件仍不清楚，并且存在相互矛盾的报告。在这里，我们分析了 的各种菌株，这是革兰氏阳性菌的模型，我们表明 MreB 在活跃生长过程中平均形成亚衍射限制的、小于 200nm 的纳米纤维，而微米长的纤维是由于蛋白质的人工过度积累造成的。我们的结果还表明，纤维的大小对其速度、方向和其他动态特性没有影响，从而赋予 MreB 聚合物较大的耐受性。我们的数据表明，无论 MreB 水平如何，各种菌株中移动纤维的密度保持不变，这表明另一个因素决定了这个常数。细菌细胞包膜的构建是一个基本的主题，因为它赋予了细菌的完整性，因此是许多抗生素的目标。MreB 是一种被怀疑调节细胞壁合成机械的必需蛋白。尽管经过了二十年的研究，其定位仍然存在争议，从跨越整个细胞的螺旋纤维到小的离散实体都有描述。这些纤维的真实结构很重要，因为它影响描述细胞壁合成机械如何相关、如何在整个细胞的尺度上协调以及 MreB 如何介导这种调节的模型。我们的结果揭示了生长过程中 中天然纤维的大小，为这一争论提供了线索。它们反对 MreB 纤维大小直接影响细胞壁合成速度的模型，以及 MreB 沿侧壁协调远距离机械的模型。
