Two Distinct Conformations in 34 FliF Subunits Generate Three Different Symmetries within the Flagellar MS-Ring
| Autor: | Katsumi Imada, Michio Homma, Norihiro Takekawa, Takayuki Kato, Mayuko Sakuma, Akihiro Kawamoto, Seiji Kojima, Keiichi Namba, Tohru Minamino, Miki Kinoshita |
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| Rok vydání: | 2021 |
| Předmět: |
Molecular Biology and Physiology
Cryo-electron microscopy Flagellum Ring (chemistry) Crystallography X-Ray Microbiology Protein Structure Secondary 03 medical and health sciences Bacterial Proteins type III secretion Virology Organelle 030304 developmental biology 0303 health sciences bacterial flagellar motor Chemistry 030302 biochemistry & molecular biology Cryoelectron Microscopy Membrane Proteins Periplasmic space MS-ring QR1-502 Transmembrane protein Molecular Docking Simulation Transmembrane domain Cytoplasm Flagella Biophysics rotor Research Article |
| Zdroj: | mBio mBio, Vol 12, Iss 2 (2021) |
| ISSN: | 2150-7511 |
| Popis: | 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. The bacterial flagellum is a protein nanomachine essential for bacterial motility. The flagellar basal body contains several ring structures. The MS-ring is embedded in the cytoplasmic membrane and is formed at the earliest stage of flagellar formation to serve as the base for flagellar assembly as well as a housing for the flagellar protein export gate complex. The MS-ring is formed by FliF, which has two transmembrane helices and a large periplasmic region. A recent electron cryomicroscopy (cryoEM) study of the MS-ring formed by overexpressed FliF revealed a symmetry mismatch between the S-ring and inner part of the M-ring. However, the actual symmetry relation in the native MS-ring and positions of missing domains remain obscure. Here, we show the structure of the M-ring by combining cryoEM and X-ray crystallography. The crystal structure of the N-terminal half of the periplasmic region of FliF showed that it consists of two domains (D1 and D2) resembling PrgK D1/PrgH D2 and PrgK D2/PrgH D3 of the injectisome. CryoEM analysis revealed that the inner part of the M-ring shows a gear wheel-like density with the inner ring of C23 symmetry surrounded by cogs with C11 symmetry, to which 34 copies of FliFD1–D2 fitted well. We propose that FliFD1–D2 adopts two distinct orientations in the M-ring relative to the rest of FliF, with 23 chains forming the wheel and 11 chains forming the cogs, and the 34 chains come together to form the S-ring with C34 symmetry for multiple functions of the MS-ring. |
| Databáze: | OpenAIRE |
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