Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, USA.
J Biol Chem. 2012 Oct 19;287(43):35779-83. doi: 10.1074/jbc.C112.378380. Epub 2012 Aug 15.
The flagellar motor is one type of propulsion device of motile bacteria. The cytoplasmic ring (C-ring) of the motor interacts with the stator to generate torque in clockwise and counterclockwise directions. The C-ring is composed of three proteins, FliM, FliN, and FliG. Together they form the "switch complex" and regulate switching and torque generation. Here we report the crystal structure of the middle domain of FliM in complex with the middle and C-terminal domains of FliG that shows the interaction surface and orientations of the proteins. In the complex, FliG assumes a compact conformation in which the middle and C-terminal domains (FliG(MC)) collapse and stack together similarly to the recently published structure of a mutant of FliG(MC) with a clockwise rotational bias. This intramolecular stacking of the domains is distinct from the intermolecular stacking seen in other structures of FliG. We fit the complex structure into the three-dimensional reconstructions of the motor and propose that the cytoplasmic ring is assembled from 34 FliG and FliM molecules in a 1:1 fashion.
鞭毛马达是运动细菌的一种推进装置。马达的细胞质环（C 环）与定子相互作用，产生顺时针和逆时针方向的扭矩。C 环由三种蛋白质组成，FliM、FliN 和 FliG。它们共同构成了“开关复合物”，调节开关和扭矩的产生。在这里，我们报告了 FliM 中间结构域与 FliG 的中间和 C 末端结构域形成复合物的晶体结构，显示了蛋白质的相互作用表面和取向。在复合物中，FliG 呈现出紧凑的构象，其中中间和 C 末端结构域（FliG(MC)）坍塌并堆积在一起，类似于最近报道的具有顺时针旋转偏差的 FliG(MC)突变体的结构。这种结构域的分子内堆积与其他 FliG 结构中观察到的分子间堆积不同。我们将复合物结构拟合到马达的三维重建中，并提出细胞质环由 34 个 FliG 和 FliM 分子以 1:1 的比例组装而成。
