Assembly and glycosylation of <i>Helicobacter pylori</i> sheathed flagella

We present the first <i>in-situ</i> near-atomic structure of the sheathed flagellar filament in <i>Helicobacter pylori</i> , revealing distinctive adaptations that underpin the pathogen's unique motility and persistent infection. Our <i>in-situ</i> structures show that the two flagellins, FlaA and FlaB, assemble into an extended and exceptionally stable filament through an extensive hydrogen-bonding network. Pseudaminic acid glycans decorate the surface-exposed domains, where they stabilize inter-subunit packing and render the surface negatively charged and hydrophilic. These findings, which provide insight into the assembly of the flagellar filament and its relationship to the surrounding sheath, provide a structural framework for developing strategies to disrupt <i>H. pylori</i> motility and infection.