Two Distinct Conformations in 34 FliF Subunits Generate Three Different Symmetries within the Flagellar MS-Ring
Norihiro Takekawa, Akihiro Kawamoto, Mayuko Sakuma, Takayuki Kato, Seiji Kojima, Miki Kinoshita, Tohru Minamino, Keiichi Namba, Michio Homma, Katsumi Imada
Abstract
The bacterial flagellum is a motility organelle formed by tens of thousands of protein molecules. At the earliest stage of flagellar assembly, a transmembrane protein, FliF, forms the MS-ring in the cytoplasmic membrane as the base for flagellar assembly. Here, we solved the crystal structure of a FliF fragment. Electron cryomicroscopy (cryoEM) structural analysis of the MS-ring showed that the M-ring and S-ring have different rotational symmetries. By docking the crystal structure of the FliF fragment into the cryoEM density map of the entire MS-ring, we built a model of the whole periplasmic region of FliF and proposed that FliF adopts two distinct conformations to generate three distinct C11, C23, and C34 symmetries within the MS-ring for its multiple functions.