Oligomerization of the FliF Domains Suggests a Coordinated Assembly of the Bacterial Flagellum MS Ring.
Oligomerization of the FliF Domains Suggests a Coordinated Assembly of the Bacterial Flagellum MS Ring.
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DOI：
10.3389/fmicb.2021.781960
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发表时间：
2021
影响因子：
5.2
通讯作者：
Bergeron JRC
中科院分区：
文献类型：
--
作者：
Mariano G;Faba-Rodriguez R;Bui S;Zhao W;Ross J;Tzokov SB;Bergeron JRC
细菌鞭毛是一个复杂的，自我组装的大分子机器，为细菌的运动提供动力。它在细菌毒力中起着不同的作用，包括在感染期间帮助定植和传播。鞭毛由从细胞突出的丝状结构和基体组成，基体是跨越细胞被膜的大型组件。基体由超过20种不同的蛋白质组成，形成几个同心环结构，分别称为M-S-L-P-和C-环。特别地，MS环由单个蛋白FliF形成，其由将其锚定到内膜并围绕大的周质结构域的两个跨膜螺旋组成。通过FliF的低聚反应组装MS环是基体组装的第一步之一。先前的计算分析表明，FliF的周质区由三个结构相似的结构域组成，称为Ring-Building Motif（RBM）1、RBM 2和RBM 3。MS-环的结构最近已被报道，并且出乎意料地显示这三个结构域采用不同的对称性，RBM 3具有34-mer化学计量，而RBM 2在复合物中采用两个不同的位置，包括23-mer环。这一观察结果提出了一些关于MS环组装的重要问题，以及在单个蛋白质中形成这种对称性错配的问题。在这项研究中，我们分析了肠道沙门氏菌血清型鼠伤寒FliF直系同源物中单独RBM结构域的寡聚化。我们证明了FliF的周质结构域在没有跨膜螺旋的情况下组装成MS环。我们还报告说，RBM 2和RBM 3域寡聚成环结构，但不是RBM 1。有趣的是，我们观察到包含RBM 1和RBM 2的构建体是单体的，这表明RBM 1与RBM 2相互作用，并抑制其寡聚化。然而，这种抑制通过添加RBM 3而解除。总的来说，这些数据表明MS环的受控组装的机制。
The bacterial flagellum is a complex, self-assembling macromolecular machine that powers bacterial motility. It plays diverse roles in bacterial virulence, including aiding in colonization and dissemination during infection. The flagellum consists of a filamentous structure protruding from the cell, and of the basal body, a large assembly that spans the cell envelope. The basal body is comprised of over 20 different proteins forming several concentric ring structures, termed the M- S- L- P- and C-rings, respectively. In particular, the MS rings are formed by a single protein FliF, which consists of two trans-membrane helices anchoring it to the inner membrane and surrounding a large periplasmic domain. Assembly of the MS ring, through oligomerization of FliF, is one of the first steps of basal body assembly. Previous computational analysis had shown that the periplasmic region of FliF consists of three structurally similar domains, termed Ring-Building Motif (RBM)1, RBM2, and RBM3. The structure of the MS-ring has been reported recently, and unexpectedly shown that these three domains adopt different symmetries, with RBM3 having a 34-mer stoichiometry, while RBM2 adopts two distinct positions in the complex, including a 23-mer ring. This observation raises some important question on the assembly of the MS ring, and the formation of this symmetry mismatch within a single protein. In this study, we analyze the oligomerization of the individual RBM domains in isolation, in the Salmonella enterica serovar Typhimurium FliF ortholog. We demonstrate that the periplasmic domain of FliF assembles into the MS ring, in the absence of the trans-membrane helices. We also report that the RBM2 and RBM3 domains oligomerize into ring structures, but not RBM1. Intriguingly, we observe that a construct encompassing RBM1 and RBM2 is monomeric, suggesting that RBM1 interacts with RBM2, and inhibits its oligomerization. However, this inhibition is lifted by the addition of RBM3. Collectively, this data suggest a mechanism for the controlled assembly of the MS ring.