Many bacteria swim by rotating flagella. The chemotaxis system controls the direction of flagellar rotation. Vibrio alginolyticus, which has a single polar flagellum, swims smoothly by rotating the flagellar motor counterclockwise (CCW) in response to attractants. In response to repellents, the motor frequently switches its rotational direction between CCW and clockwise (CW). We isolated a mutant strain that swims with a CW-locked rotation of the flagellum, which pulls rather than pushes the cell. This CW phenotype arises from a R49P substitution in FliM, which is the component in the C-ring of the motor that binds the chemotaxis signalling protein, phosphorylated CheY. However, this phenotype is independent of CheY, indicating that the mutation produces a CW conformation of the C-ring in the absence of CheY. The crystal structure of FliM with the R49P substitution showed a conformational change in the N-terminal α-helix of the middle domain of FliM (FliMM). This helix should mediates FliM–FliM interaction. The structural models of wild type and mutant C-ring showed that the relatively small conformational change in FliMM induces a drastic rearrangement of the conformation of the FliMM domain that generates a CW conformation of the C-ring.

中文翻译：

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FliM 中 α 螺旋的轻微弯曲会在弧菌中产生逆时针锁定的鞭毛马达结构

许多细菌通过旋转鞭毛游泳。趋化系统控制鞭毛旋转的方向。溶藻弧菌具有单极鞭毛，通过逆时针旋转鞭毛马达 (CCW) 以响应引诱物，从而顺畅地游动。为响应驱虫剂，电机经常在 CCW 和顺时针 (CW) 之间切换其旋转方向。我们分离出一种突变株，它会随着鞭毛的 CW 锁定旋转而游动，它会拉动而不是推动细胞。这种 CW 表型源于 FliM 中的 R49P 替代，它是马达 C 环中的成分，可与趋化性信号蛋白磷酸化 CheY 结合。然而，这种表型与 CheY 无关，表明该突变在没有 CheY 的情况下产生 C 环的 CW 构象。具有 R49P 取代的 FliM 的晶体结构显示出 FliM 中间结构域 (FliMM) 的 N 末端 α-螺旋的构象变化。这个螺旋应该介导 FliM-FliM 相互作用。野生型和突变型 C 环的结构模型表明，FliMM 中相对较小的构象变化会导致 FliMM 结构域的构象发生剧烈重排，从而产生 C 环的 CW 构象。