An asymmetric sheath controls flagellar supercoiling and motility in the Leptospira spirochete

Abstract

One Sentence summary: The corkscrew-like motility of Spirochete bacteria is enabled by a 29 unique, asymmetrically constructed flagellum that wraps around the cell body within the 30 periplasm. 31 Abstract: Spirochete bacteria, including important pathogens, exhibit a distinctive means of 32 swimming via undulations of the entire cell. Motility is powered by the rotation of supercoiled 33 'endoflagella' that wrap around the cell body, confined within the periplasmic space. To 34 investigate the structural basis of flagellar supercoiling, which is critical for motility, we 35 determined the structure of native flagellar filaments from the spirochete Leptospira by 36 integrating high-resolution cryo-electron tomography and X-ray crystallography. We show that 37 these filaments are coated by a highly asymmetric, multi-component sheath layer, contrasting 38 with flagellin-only homopolymers previously observed in exoflagellated bacteria. Distinct sheath 39 proteins localize to the filament inner and outer curvatures to define the supercoiling geometry, 40 explaining a key functional attribute of the spirochete flagellum.41