Two Distinct Conformations in 34 FliF Subunits Generate Three Different Symmetries within the Flagellar MS-Ring

摘要: The bacterial flagellum is a protein nanomachine essential for motility. flagellar basal body contains several ring structures. MS-ring embedded in the cytoplasmic membrane and formed at earliest stage of formation to serve as base assembly well housing export gate complex. by FliF, which has two transmembrane helices large periplasmic region. A recent electron cryomicroscopy (cryoEM) study overexpressed FliF revealed symmetry mismatch between S-ring inner part M-ring. However, actual relation native positions missing domains remain obscure. Here, we show structure M-ring combining cryoEM X-ray crystallography. crystal N-terminal half region showed that it consists (D1 D2) resembling PrgK D1/PrgH D2 D2/PrgH D3 injectisome. CryoEM analysis shows gear wheel-like density with C23 surrounded cogs C11 symmetry, 34 copies FliFD1-D2 fitted well. We propose adopts distinct orientations relative rest 23 chains forming wheel 11 cogs, come together form C34 multiple functions MS-ring.IMPORTANCE motility organelle tens thousands molecules. At assembly, protein, forms assembly. solved fragment. Electron structural have different rotational symmetries. By docking fragment into map entire MS-ring, built model whole proposed conformations generate three C11, C23, symmetries within its functions.